From: Sam Hartman <hartmans@debian.org>
Date: Thu, 26 Jun 2025 11:09:29 -0600
Subject: pam_namespace from v1.7.1

Pull in pam_namespace from v1.7.1. We did not have any local changes,
and this includes the fix for CVE-2025-6020.

The commits fall into the following categories:
 * specific to this security issue

 * error handling issues that are very likely correct and that it is
   easier to take than to convince ourselves cannot be exploited in their
   own right.

 * Cleanup that made the patch for this security issue easier to audit
   and that created abstractions needed by the patch for this security
   issue.  I.E. it's obvious that since the issue was reported the
   maintainers and reporters were working on cleaning up the code to get
   a cleaner patch to this issue.

 * harmless (replacing needless asprintf with strdup)
---
 modules/pam_namespace/namespace.conf.5.xml |    2 +-
 modules/pam_namespace/namespace.init       |   56 +-
 modules/pam_namespace/pam_namespace.8.xml  |    2 +-
 modules/pam_namespace/pam_namespace.c      | 1122 ++++++++++++++++++----------
 modules/pam_namespace/pam_namespace.h      |   14 +-
 5 files changed, 770 insertions(+), 426 deletions(-)

diff --git a/modules/pam_namespace/namespace.conf.5.xml b/modules/pam_namespace/namespace.conf.5.xml
index 15aef5c..54f9431 100644
--- a/modules/pam_namespace/namespace.conf.5.xml
+++ b/modules/pam_namespace/namespace.conf.5.xml
@@ -226,7 +226,7 @@
     <para>
       <citerefentry><refentrytitle>pam_namespace</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
       <citerefentry><refentrytitle>pam.d</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
-      <citerefentry><refentrytitle>pam</refentrytitle><manvolnum>7</manvolnum></citerefentry>
+      <citerefentry><refentrytitle>pam</refentrytitle><manvolnum>8</manvolnum></citerefentry>
     </para>
   </refsect1>
 
diff --git a/modules/pam_namespace/namespace.init b/modules/pam_namespace/namespace.init
index 1a6b624..8782178 100755
--- a/modules/pam_namespace/namespace.init
+++ b/modules/pam_namespace/namespace.init
@@ -1,25 +1,43 @@
 #!/bin/sh
-# It receives polydir path as $1, the instance path as $2,
-# a flag whether the instance dir was newly created (0 - no, 1 - yes) in $3,
-# and user name in $4.
+# It receives as arguments:
+# - $1 polydir path (see WARNING below)
+# - $2 instance path (see WARNING below)
+# - $3 flag whether the instance dir was newly created (0 - no, 1 - yes)
+# - $4 user name
+# - $5 flag whether the polydir path ($1) is safe (0 - unsafe, 1 -safe)
+# - $6 flag whether the instance path ($2) is safe (0 - unsafe, 1 - safe)
+#
+# WARNING: This script is invoked with full root privileges. Accessing
+# the polydir ($1) and the instance ($2) directories in this context may be
+# extremely dangerous as those can be under user control. The flags $5 and $6
+# are provided to let you know if all the segments part of the path (except the
+# last one) are owned by root and are writable by root only. If the path does
+# not meet these criteria, you expose yourself to possible symlink attacks when
+# accessing these path.
+# However, even if the path components are safe, the content of the
+# directories may still be owned/writable by a user, so care must be taken!
 #
 # The following section will copy the contents of /etc/skel if this is a
 # newly created home directory.
-if [ "$3" = 1 ]; then
-        # This line will fix the labeling on all newly created directories
-        [ -x /sbin/restorecon ] && /sbin/restorecon "$1"
-        user="$4"
-        passwd=$(getent passwd "$user")
-        homedir=$(echo "$passwd" | cut -f6 -d":")
-        if [ "$1" = "$homedir" ]; then
-                gid=$(echo "$passwd" | cut -f4 -d":")
-                cp -rT /etc/skel "$homedir"
-                chown -R "$user":"$gid" "$homedir"
-                mask=$(sed -E -n 's/^UMASK[[:space:]]+([^#[:space:]]+).*/\1/p' /etc/login.defs)
-                mode=$(printf "%o" $((0777 & ~mask)))
-                chmod ${mode:-700} "$homedir"
-                [ -x /sbin/restorecon ] && /sbin/restorecon -R "$homedir"
-        fi
-fi
 
+# Executes only if the polydir path is safe
+if [ "$5" = 1 ]; then
+
+    if [ "$3" = 1 ]; then
+            # This line will fix the labeling on all newly created directories
+            [ -x /sbin/restorecon ] && /sbin/restorecon "$1"
+            user="$4"
+            passwd=$(getent passwd "$user")
+            homedir=$(echo "$passwd" | cut -f6 -d":")
+            if [ "$1" = "$homedir" ]; then
+                    gid=$(echo "$passwd" | cut -f4 -d":")
+                    cp -rT /etc/skel "$homedir"
+                    chown -R "$user":"$gid" "$homedir"
+                    mask=$(sed -E -n 's/^UMASK[[:space:]]+([^#[:space:]]+).*/\1/p' /etc/login.defs)
+                    mode=$(printf "%o" $((0777 & ~mask)))
+                    chmod ${mode:-700} "$homedir"
+                    [ -x /sbin/restorecon ] && /sbin/restorecon -R "$homedir"
+            fi
+    fi
+fi
 exit 0
diff --git a/modules/pam_namespace/pam_namespace.8.xml b/modules/pam_namespace/pam_namespace.8.xml
index 0896372..a866d2e 100644
--- a/modules/pam_namespace/pam_namespace.8.xml
+++ b/modules/pam_namespace/pam_namespace.8.xml
@@ -392,7 +392,7 @@
         <refentrytitle>mount</refentrytitle><manvolnum>8</manvolnum>
       </citerefentry>,
       <citerefentry>
-        <refentrytitle>pam</refentrytitle><manvolnum>7</manvolnum>
+        <refentrytitle>pam</refentrytitle><manvolnum>8</manvolnum>
       </citerefentry>.
     </para>
   </refsect1>
diff --git a/modules/pam_namespace/pam_namespace.c b/modules/pam_namespace/pam_namespace.c
index ba7910f..e7ff5b3 100644
--- a/modules/pam_namespace/pam_namespace.c
+++ b/modules/pam_namespace/pam_namespace.c
@@ -41,6 +41,8 @@
 #include "pam_namespace.h"
 #include "argv_parse.h"
 
+#define MAGIC_LNK_FD_SIZE 64
+
 /* --- evaluating all files in VENDORDIR/security/namespace.d and /etc/security/namespace.d --- */
 static const char *base_name(const char *path)
 {
@@ -63,6 +65,275 @@ static void close_fds_pre_exec(struct instance_data *idata)
 	}
 }
 
+static void
+strip_trailing_slashes(char *str)
+{
+	char *p = str + strlen(str);
+
+	while (--p > str && *p == '/')
+		*p = '\0';
+}
+
+static int protect_mount(int dfd, const char *path, struct instance_data *idata)
+{
+	struct protect_dir_s *dir = idata->protect_dirs;
+	char tmpbuf[MAGIC_LNK_FD_SIZE];
+
+	while (dir != NULL) {
+		if (strcmp(path, dir->dir) == 0) {
+			return 0;
+		}
+		dir = dir->next;
+	}
+
+	if (pam_sprintf(tmpbuf, "/proc/self/fd/%d", dfd) < 0)
+		return -1;
+
+	dir = calloc(1, sizeof(*dir));
+
+	if (dir == NULL) {
+		return -1;
+	}
+
+	dir->dir = strdup(path);
+
+	if (dir->dir == NULL) {
+		free(dir);
+		return -1;
+	}
+
+	if (idata->flags & PAMNS_DEBUG) {
+		pam_syslog(idata->pamh, LOG_INFO,
+			"Protect mount of %s over itself", path);
+	}
+
+	if (mount(tmpbuf, tmpbuf, NULL, MS_BIND, NULL) != 0) {
+		int save_errno = errno;
+		pam_syslog(idata->pamh, LOG_ERR,
+			"Protect mount of %s failed: %m", tmpbuf);
+		free(dir->dir);
+		free(dir);
+		errno = save_errno;
+		return -1;
+	}
+
+	dir->next = idata->protect_dirs;
+	idata->protect_dirs = dir;
+
+	return 0;
+}
+
+/*
+ * Returns a fd to the given absolute path, acquired securely. This means:
+ * - iterating on each segment of the path,
+ * - not following user symlinks,
+ * - using race-free operations.
+ *
+ * Takes a bit mask to specify the operation mode:
+ * - SECURE_OPENDIR_PROTECT: call protect_mount() on each unsafe segment of path
+ * - SECURE_OPENDIR_MKDIR: create last segment of path if does not exist
+ * - SECURE_OPENDIR_FULL_FD: open the directory with O_RDONLY instead of O_PATH,
+ *     allowing more operations to be done with the returned fd
+ *
+ * Be aware that using SECURE_OPENDIR_PROTECT:
+ * - will modify some external state (global structure...) and should not be
+ *   called in cleanup code paths. See wrapper secure_opendir_stateless()
+ * - need a non-NULL idata to call protect_mount()
+ */
+static int secure_opendir(const char *path, int opm, mode_t mode,
+	struct instance_data *idata)
+{
+	char *p;
+	char *d;
+	char *dir;
+	int dfd = -1;
+	int dfd_next;
+	int save_errno;
+	int flags = O_DIRECTORY | O_CLOEXEC;
+	int rv = -1;
+	struct stat st;
+
+	if (opm & SECURE_OPENDIR_FULL_FD)
+		flags |= O_RDONLY;
+	else
+		flags |= O_PATH;
+
+	/* Check for args consistency */
+	if ((opm & SECURE_OPENDIR_PROTECT) && idata == NULL)
+		return -1;
+
+	/* Accept only absolute paths */
+	if (*path != '/')
+		return -1;
+
+	dir = p = strdup(path);
+	if (p == NULL)
+		return -1;
+
+	/* Assume '/' is safe */
+	dfd = open("/", flags);
+	if (dfd == -1)
+		goto error;
+
+	/* Needed to not loop too far and call openat() on NULL */
+	strip_trailing_slashes(p);
+
+	dir++;
+
+	/* In case path is '/' */
+	if (*dir == '\0') {
+		free(p);
+		return dfd;
+	}
+
+	while ((d=strchr(dir, '/')) != NULL) {
+		*d = '\0';
+
+		dfd_next = openat(dfd, dir, flags);
+		if (dfd_next == -1)
+			goto error;
+
+		if (fstat(dfd_next, &st) != 0) {
+			close(dfd_next);
+			goto error;
+		}
+
+		if ((flags & O_NOFOLLOW) && (opm & SECURE_OPENDIR_PROTECT)) {
+			/* we are inside user-owned dir - protect */
+			if (protect_mount(dfd_next, p, idata) == -1) {
+				close(dfd_next);
+				goto error;
+			}
+			/*
+			 * Reopen the directory to obtain a new descriptor
+			 * after protect_mount(), this is necessary in cases
+			 * when another directory is going to be mounted over
+			 * the given path.
+			 */
+			close(dfd_next);
+			dfd_next = openat(dfd, dir, flags);
+			if (dfd_next == -1)
+				goto error;
+		} else if (st.st_uid != 0
+		           || (st.st_mode & (S_IWGRP|S_IWOTH))) {
+			/* do not follow symlinks on subdirectories */
+			flags |= O_NOFOLLOW;
+		}
+
+		close(dfd);
+		dfd = dfd_next;
+
+		*d = '/';
+		dir = d + 1;
+	}
+
+	rv = openat(dfd, dir, flags);
+
+	if (rv == -1) {
+		if ((opm & SECURE_OPENDIR_MKDIR) && mkdirat(dfd, dir, mode) == 0)
+			rv = openat(dfd, dir, flags);
+
+		if (rv == -1)
+			goto error;
+	}
+
+	if ((flags & O_NOFOLLOW) && (opm & SECURE_OPENDIR_PROTECT)) {
+		/* we are inside user-owned dir - protect */
+		if (protect_mount(rv, p, idata) == -1) {
+			save_errno = errno;
+			close(rv);
+			rv = -1;
+			errno = save_errno;
+		}
+		/*
+		 * Reopen the directory to obtain a new descriptor after
+		 * protect_mount(), this is necessary in cases when another
+		 * directory is going to be mounted over the given path.
+		 */
+		close(rv);
+		rv = openat(dfd, dir, flags);
+	}
+
+error:
+	save_errno = errno;
+	free(p);
+	if (dfd >= 0)
+		close(dfd);
+	errno = save_errno;
+
+	return rv;
+}
+
+/*
+ * Returns a fd to the given path, acquired securely.
+ * It can be called in all situations, including in cleanup code paths, as
+ * it does not modify external state (no access to global structures...).
+ */
+static int secure_opendir_stateless(const char *path)
+{
+	return secure_opendir(path, 0, 0, NULL);
+}
+
+/*
+ * Umount securely the given path, even if the directories along
+ * the path are under user control. It should protect against
+ * symlinks attacks and race conditions.
+ */
+static int secure_umount(const char *path)
+{
+	int save_errno;
+	int rv = -1;
+	int dfd = -1;
+	char s_path[MAGIC_LNK_FD_SIZE];
+
+	dfd = secure_opendir_stateless(path);
+	if (dfd == -1)
+		return rv;
+
+	if (pam_sprintf(s_path, "/proc/self/fd/%d", dfd) < 0)
+		goto error;
+
+	/*
+	* We still have a fd open to path itself,
+	* so we need to do a lazy umount.
+	*/
+	rv = umount2(s_path, MNT_DETACH);
+
+error:
+	save_errno = errno;
+	close(dfd);
+	errno = save_errno;
+	return rv;
+}
+
+/*
+ * Rmdir the given path securely, protecting against symlinks attacks
+ * and race conditions.
+ * This function is currently called only in cleanup code paths where
+ * any errors returned are not handled, so do not handle them either.
+ * Basically, try to rmdir the path on a best-effort basis.
+ */
+static void secure_try_rmdir(const char *path)
+{
+	int dfd;
+	char *buf;
+	char *parent;
+
+	buf = strdup(path);
+	if (buf == NULL)
+		return;
+
+	parent = dirname(buf);
+
+	dfd = secure_opendir_stateless(parent);
+	if (dfd >= 0) {
+		unlinkat(dfd, base_name(path), AT_REMOVEDIR);
+		close(dfd);
+	}
+
+	free(buf);
+}
+
 /* Evaluating a list of files which have to be parsed in the right order:
  *
  * - If etc/security/namespace.d/@filename@.conf exists, then
@@ -188,7 +459,7 @@ static void unprotect_dirs(struct protect_dir_s *dir)
 	struct protect_dir_s *next;
 
 	while (dir != NULL) {
-		umount(dir->dir);
+		secure_umount(dir->dir);
 		free(dir->dir);
 		next = dir->next;
 		free(dir);
@@ -319,8 +590,7 @@ static int parse_iscript_params(char *params, struct polydir_s *poly)
 
     if (*params != '\0') {
 	if (*params != '/') { /* path is relative to NAMESPACE_D_DIR */
-		if (asprintf(&poly->init_script, "%s%s", NAMESPACE_D_DIR, params) == -1)
-			return -1;
+		poly->init_script = pam_asprintf("%s%s", NAMESPACE_D_DIR, params);
 	} else {
 		poly->init_script = strdup(params);
 	}
@@ -482,6 +752,7 @@ static int process_line(char *line, const char *home, const char *rhome,
 			struct instance_data *idata)
 {
     char *dir = NULL, *instance_prefix = NULL, *rdir = NULL;
+    const char *config_dir, *config_instance_prefix;
     char *method, *uids;
     char *tptr;
     struct polydir_s *poly;
@@ -490,7 +761,6 @@ static int process_line(char *line, const char *home, const char *rhome,
     static const char *const var_names[] = {"HOME", "USER", NULL};
     const char *var_values[] = {home, idata->user};
     const char *rvar_values[] = {rhome, idata->ruser};
-    size_t len;
 
     /*
      * skip the leading white space
@@ -531,22 +801,19 @@ static int process_line(char *line, const char *home, const char *rhome,
         goto erralloc;
     }
 
-    dir = config_options[0];
-    if (dir == NULL) {
+    config_dir = config_options[0];
+    if (config_dir == NULL) {
         pam_syslog(idata->pamh, LOG_NOTICE, "Invalid line missing polydir");
         goto skipping;
     }
-    instance_prefix = config_options[1];
-    if (instance_prefix == NULL) {
+    config_instance_prefix = config_options[1];
+    if (config_instance_prefix == NULL) {
         pam_syslog(idata->pamh, LOG_NOTICE, "Invalid line missing instance_prefix");
-        dir = NULL;
         goto skipping;
     }
     method = config_options[2];
     if (method == NULL) {
         pam_syslog(idata->pamh, LOG_NOTICE, "Invalid line missing method");
-        instance_prefix = NULL;
-        dir = NULL;
         goto skipping;
     }
 
@@ -561,19 +828,16 @@ static int process_line(char *line, const char *home, const char *rhome,
     /*
      * Expand $HOME and $USER in poly dir and instance dir prefix
      */
-    if ((rdir=expand_variables(dir, var_names, rvar_values)) == NULL) {
-	    instance_prefix = NULL;
-	    dir = NULL;
+    if ((rdir = expand_variables(config_dir, var_names, rvar_values)) == NULL) {
 	    goto erralloc;
     }
 
-    if ((dir=expand_variables(dir, var_names, var_values)) == NULL) {
-	    instance_prefix = NULL;
+    if ((dir = expand_variables(config_dir, var_names, var_values)) == NULL) {
 	    goto erralloc;
     }
 
-    if ((instance_prefix=expand_variables(instance_prefix, var_names, var_values))
-	    == NULL) {
+    if ((instance_prefix = expand_variables(config_instance_prefix,
+					    var_names, var_values)) == NULL) {
 	    goto erralloc;
     }
 
@@ -583,15 +847,8 @@ static int process_line(char *line, const char *home, const char *rhome,
 	    pam_syslog(idata->pamh, LOG_DEBUG, "Expanded instance prefix: '%s'", instance_prefix);
     }
 
-    len = strlen(dir);
-    if (len > 0 && dir[len-1] == '/') {
-	    dir[len-1] = '\0';
-    }
-
-    len = strlen(rdir);
-    if (len > 0 && rdir[len-1] == '/') {
-	    rdir[len-1] = '\0';
-    }
+    strip_trailing_slashes(dir);
+    strip_trailing_slashes(rdir);
 
     if (dir[0] == '\0' || rdir[0] == '\0') {
 	    pam_syslog(idata->pamh, LOG_NOTICE, "Invalid polydir");
@@ -606,14 +863,9 @@ static int process_line(char *line, const char *home, const char *rhome,
 	    goto skipping;
     }
 
-#define COPY_STR(dst, src, apd)                                \
-	(snprintf((dst), sizeof(dst), "%s%s", (src), (apd)) != \
-		  (ssize_t) (strlen(src) + strlen(apd)))
-
-    if (COPY_STR(poly->dir, dir, "")
-	|| COPY_STR(poly->rdir, rdir, "")
-	|| COPY_STR(poly->instance_prefix, instance_prefix,
-		    poly->method == TMPDIR ? "XXXXXX" : "")) {
+    if (pam_sprintf(poly->dir, "%s", dir) < 0
+	|| pam_sprintf(poly->rdir, "%s", rdir) < 0
+	|| pam_sprintf(poly->instance_prefix, "%s", instance_prefix) < 0) {
 	pam_syslog(idata->pamh, LOG_NOTICE, "Pathnames too long");
 	goto skipping;
     }
@@ -896,6 +1148,23 @@ static char *md5hash(const char *instname, struct instance_data *idata)
 }
 
 #ifdef WITH_SELINUX
+static char *secure_getfilecon(pam_handle_t *pamh, const char *dir)
+{
+	char *ctx = NULL;
+	int dfd = secure_opendir(dir, SECURE_OPENDIR_FULL_FD, 0, NULL);
+	if (dfd < 0) {
+		pam_syslog(pamh, LOG_ERR, "Error getting fd to %s: %m", dir);
+		return NULL;
+	}
+	if (fgetfilecon(dfd, &ctx) < 0)
+		ctx = NULL;
+	if (ctx == NULL)
+		pam_syslog(pamh, LOG_ERR,
+			   "Error getting poly dir context for %s: %m", dir);
+	close(dfd);
+	return ctx;
+}
+
 static int form_context(const struct polydir_s *polyptr,
 		char **i_context, char **origcon,
 		struct instance_data *idata)
@@ -907,12 +1176,9 @@ static int form_context(const struct polydir_s *polyptr,
 	/*
 	 * Get the security context of the directory to polyinstantiate.
 	 */
-	rc = getfilecon(polyptr->dir, origcon);
-	if (rc < 0 || *origcon == NULL) {
-		pam_syslog(idata->pamh, LOG_ERR,
-				"Error getting poly dir context, %m");
+	*origcon = secure_getfilecon(idata->pamh, polyptr->dir);
+	if (*origcon == NULL)
 		return PAM_SESSION_ERR;
-	}
 
 	if (polyptr->method == USER) return PAM_SUCCESS;
 
@@ -1009,29 +1275,52 @@ static int form_context(const struct polydir_s *polyptr,
 #endif
 
 /*
- * poly_name returns the name of the polyinstantiated instance directory
+ * From the instance differentiation string, set in the polyptr structure:
+ * - the absolute path to the instance dir,
+ * - the absolute path to the previous dir (parent),
+ * - the instance name (may be different than the instance differentiation string)
+ */
+static int set_polydir_paths(struct polydir_s *polyptr, const char *inst_differentiation)
+{
+	char *tmp;
+
+	if (pam_sprintf(polyptr->instance_absolute, "%s%s",
+	                polyptr->instance_prefix, inst_differentiation) < 0)
+		return -1;
+
+	polyptr->instname = strrchr(polyptr->instance_absolute, '/') + 1;
+
+	if (pam_sprintf(polyptr->instance_parent, "%s", polyptr->instance_absolute) < 0)
+		return -1;
+
+	tmp = strrchr(polyptr->instance_parent, '/') + 1;
+	*tmp = '\0';
+
+	return 0;
+}
+
+/*
+ * Set the name of the polyinstantiated instance directory
  * based on the method used for polyinstantiation (user, context or level)
  * In addition, the function also returns the security contexts of the
  * original directory to polyinstantiate and the polyinstantiated instance
  * directory.
  */
 #ifdef WITH_SELINUX
-static int poly_name(const struct polydir_s *polyptr, char **i_name,
-	char **i_context, char **origcon,
-        struct instance_data *idata)
+static int poly_name(struct polydir_s *polyptr, char **i_context,
+        char **origcon, struct instance_data *idata)
 #else
-static int poly_name(const struct polydir_s *polyptr, char **i_name,
-	struct instance_data *idata)
+static int poly_name(struct polydir_s *polyptr, struct instance_data *idata)
 #endif
 {
     int rc;
+    char *inst_differentiation = NULL;
     char *hash = NULL;
     enum polymethod pm;
 #ifdef WITH_SELINUX
     char *rawcon = NULL;
 #endif
 
-    *i_name = NULL;
 #ifdef WITH_SELINUX
     *i_context = NULL;
     *origcon = NULL;
@@ -1065,10 +1354,8 @@ static int poly_name(const struct polydir_s *polyptr, char **i_name,
 
     switch (pm) {
         case USER:
-	    if (asprintf(i_name, "%s", idata->user) < 0) {
-		*i_name = NULL;
+	    if ((inst_differentiation = strdup(idata->user)) == NULL)
 		goto fail;
-	    }
 	    break;
 
 #ifdef WITH_SELINUX
@@ -1078,26 +1365,25 @@ static int poly_name(const struct polydir_s *polyptr, char **i_name,
 		pam_syslog(idata->pamh, LOG_ERR, "Error translating directory context");
 		goto fail;
 	    }
-	    if (polyptr->flags & POLYDIR_SHARED) {
-		if (asprintf(i_name, "%s", rawcon) < 0) {
-			*i_name = NULL;
-			goto fail;
-		}
-	    } else {
-		if (asprintf(i_name, "%s_%s", rawcon, idata->user) < 0) {
-			*i_name = NULL;
-			goto fail;
-		}
-	    }
+	    if (polyptr->flags & POLYDIR_SHARED)
+		inst_differentiation = strdup(rawcon);
+	    else
+		inst_differentiation = pam_asprintf("%s_%s", rawcon, idata->user);
+	    if (inst_differentiation == NULL)
+		goto fail;
 	    break;
 
 #endif /* WITH_SELINUX */
 
 	case TMPDIR:
-	case TMPFS:
-	    if ((*i_name=strdup("")) == NULL)
+	    if ((inst_differentiation = strdup("XXXXXX")) == NULL)
 		goto fail;
-	    return PAM_SUCCESS;
+	    goto success;
+
+	case TMPFS:
+	    if ((inst_differentiation=strdup("")) == NULL)
+		goto fail;
+	    goto success;
 
 	default:
 	    if (idata->flags & PAMNS_DEBUG)
@@ -1106,31 +1392,37 @@ static int poly_name(const struct polydir_s *polyptr, char **i_name,
     }
 
     if (idata->flags & PAMNS_DEBUG)
-        pam_syslog(idata->pamh, LOG_DEBUG, "poly_name %s", *i_name);
+        pam_syslog(idata->pamh, LOG_DEBUG, "poly_name %s", inst_differentiation);
 
-    if ((idata->flags & PAMNS_GEN_HASH) || strlen(*i_name) > NAMESPACE_MAX_DIR_LEN) {
-        hash = md5hash(*i_name, idata);
+    if ((idata->flags & PAMNS_GEN_HASH) || strlen(inst_differentiation) > NAMESPACE_MAX_DIR_LEN) {
+        hash = md5hash(inst_differentiation, idata);
         if (hash == NULL) {
 	    goto fail;
         }
         if (idata->flags & PAMNS_GEN_HASH) {
-	    free(*i_name);
-	    *i_name = hash;
+	    free(inst_differentiation);
+	    inst_differentiation = hash;
 	    hash = NULL;
         } else {
-	    char *newname;
-	    if (asprintf(&newname, "%.*s_%s", NAMESPACE_MAX_DIR_LEN-1-(int)strlen(hash),
-		*i_name, hash) < 0) {
+	    char *newname =
+		pam_asprintf("%.*s_%s",
+			     NAMESPACE_MAX_DIR_LEN - 1 - (int)strlen(hash),
+			     inst_differentiation, hash);
+	    if (newname == NULL)
 		goto fail;
-	    }
-	    free(*i_name);
-	    *i_name = newname;
+	    free(inst_differentiation);
+	    inst_differentiation = newname;
         }
     }
-    rc = PAM_SUCCESS;
 
+success:
+    if (set_polydir_paths(polyptr, inst_differentiation) == -1)
+        goto fail;
+
+    rc = PAM_SUCCESS;
 fail:
     free(hash);
+    free(inst_differentiation);
 #ifdef WITH_SELINUX
     freecon(rawcon);
 #endif
@@ -1141,189 +1433,111 @@ fail:
 	freecon(*origcon);
 	*origcon = NULL;
 #endif
-	free(*i_name);
-	*i_name = NULL;
     }
     return rc;
 }
 
-static int protect_mount(int dfd, const char *path, struct instance_data *idata)
-{
-	struct protect_dir_s *dir = idata->protect_dirs;
-	char tmpbuf[64];
-
-	while (dir != NULL) {
-		if (strcmp(path, dir->dir) == 0) {
-			return 0;
-		}
-		dir = dir->next;
-	}
-
-	dir = calloc(1, sizeof(*dir));
-
-	if (dir == NULL) {
-		return -1;
-	}
-
-	dir->dir = strdup(path);
-
-	if (dir->dir == NULL) {
-		free(dir);
-		return -1;
-	}
-
-	snprintf(tmpbuf, sizeof(tmpbuf), "/proc/self/fd/%d", dfd);
-
-	if (idata->flags & PAMNS_DEBUG) {
-		pam_syslog(idata->pamh, LOG_INFO,
-			"Protect mount of %s over itself", path);
-	}
-
-	if (mount(tmpbuf, tmpbuf, NULL, MS_BIND, NULL) != 0) {
-		int save_errno = errno;
-		pam_syslog(idata->pamh, LOG_ERR,
-			"Protect mount of %s failed: %m", tmpbuf);
-		free(dir->dir);
-		free(dir);
-		errno = save_errno;
-		return -1;
-	}
-
-	dir->next = idata->protect_dirs;
-	idata->protect_dirs = dir;
-
-	return 0;
-}
-
-static int protect_dir(const char *path, mode_t mode, int do_mkdir,
-	struct instance_data *idata)
-{
-	char *p = strdup(path);
-	char *d;
-	char *dir = p;
-	int dfd = AT_FDCWD;
-	int dfd_next;
-	int save_errno;
-	int flags = O_RDONLY | O_DIRECTORY;
-	int rv = -1;
-	struct stat st;
-
-	if (p == NULL) {
-		goto error;
-	}
-
-	if (*dir == '/') {
-		dfd = open("/", flags);
-		if (dfd == -1) {
-			goto error;
-		}
-		dir++;	/* assume / is safe */
-	}
-
-	while ((d=strchr(dir, '/')) != NULL) {
-		*d = '\0';
-		dfd_next = openat(dfd, dir, flags);
-		if (dfd_next == -1) {
-			goto error;
-		}
-
-		if (dfd != AT_FDCWD)
-			close(dfd);
-		dfd = dfd_next;
-
-		if (fstat(dfd, &st) != 0) {
-			goto error;
-		}
-
-		if (flags & O_NOFOLLOW) {
-			/* we are inside user-owned dir - protect */
-			if (protect_mount(dfd, p, idata) == -1)
-				goto error;
-		} else if (st.st_uid != 0 || st.st_gid != 0 ||
-			(st.st_mode & S_IWOTH)) {
-			/* do not follow symlinks on subdirectories */
-			flags |= O_NOFOLLOW;
-		}
-
-		*d = '/';
-		dir = d + 1;
-	}
-
-	rv = openat(dfd, dir, flags);
-
-	if (rv == -1) {
-		if (!do_mkdir || mkdirat(dfd, dir, mode) != 0) {
-			goto error;
-		}
-		rv = openat(dfd, dir, flags);
-	}
-
-	if (flags & O_NOFOLLOW) {
-		/* we are inside user-owned dir - protect */
-		if (protect_mount(rv, p, idata) == -1) {
-			save_errno = errno;
-			close(rv);
-			rv = -1;
-			errno = save_errno;
-		}
-	}
-
-error:
-	save_errno = errno;
-	free(p);
-	if (dfd != AT_FDCWD && dfd >= 0)
-		close(dfd);
-	errno = save_errno;
-
-	return rv;
-}
-
-static int check_inst_parent(char *ipath, struct instance_data *idata)
+static int check_inst_parent(int dfd, struct instance_data *idata)
 {
 	struct stat instpbuf;
-	char *inst_parent, *trailing_slash;
-	int dfd;
+
 	/*
-	 * stat the instance parent path to make sure it exists
-	 * and is a directory. Check that its mode is 000 (unless the
-	 * admin explicitly instructs to ignore the instance parent
-	 * mode by the "ignore_instance_parent_mode" argument).
+	 * Stat the instance parent directory to make sure it's writable by
+	 * root only (unless the admin explicitly instructs to ignore the
+	 * instance parent mode by the "ignore_instance_parent_mode" argument).
 	 */
-	inst_parent = strdup(ipath);
-	if (!inst_parent) {
-		pam_syslog(idata->pamh, LOG_CRIT, "Error allocating pathname string");
-		return PAM_SESSION_ERR;
-	}
 
-	trailing_slash = strrchr(inst_parent, '/');
-	if (trailing_slash)
-		*trailing_slash = '\0';
+	if (idata->flags & PAMNS_IGN_INST_PARENT_MODE)
+		return PAM_SUCCESS;
 
-	dfd = protect_dir(inst_parent, 0, 1, idata);
-
-	if (dfd == -1 || fstat(dfd, &instpbuf) < 0) {
+	if (fstat(dfd, &instpbuf) < 0) {
 		pam_syslog(idata->pamh, LOG_ERR,
-			"Error creating or accessing instance parent %s, %m", inst_parent);
-		if (dfd != -1)
-			close(dfd);
-		free(inst_parent);
+			"Error accessing instance parent, %m");
 		return PAM_SESSION_ERR;
 	}
 
-	if ((idata->flags & PAMNS_IGN_INST_PARENT_MODE) == 0) {
-		if ((instpbuf.st_mode & (S_IRWXU|S_IRWXG|S_IRWXO)) || instpbuf.st_uid != 0) {
-			pam_syslog(idata->pamh, LOG_ERR, "Mode of inst parent %s not 000 or owner not root",
-					inst_parent);
-			close(dfd);
-			free(inst_parent);
-			return PAM_SESSION_ERR;
-		}
+	if ((instpbuf.st_mode & (S_IRWXU|S_IRWXG|S_IRWXO)) || instpbuf.st_uid != 0) {
+		pam_syslog(idata->pamh, LOG_ERR,
+			"Mode of inst parent not 000 or owner not root");
+		return PAM_SESSION_ERR;
 	}
-	close(dfd);
-	free(inst_parent);
+
 	return PAM_SUCCESS;
 }
 
+/*
+ * Check for a given absolute path that all segments except the last one are:
+ * 1. a directory owned by root and not writable by group or others
+ * 2. a symlink owned by root and referencing a directory respecting 1.
+ * Returns 0 if safe, -1 is unsafe.
+ * If the path is not accessible (does not exist, hidden under a mount...),
+ * returns -1 (unsafe).
+ */
+static int check_safe_path(const char *path, struct instance_data *idata)
+{
+    char *p = strdup(path);
+    char *d;
+    char *dir = p;
+    struct stat st;
+
+    if (p == NULL)
+        return -1;
+
+    /* Check path is absolute */
+    if (p[0] != '/')
+        goto error;
+
+    strip_trailing_slashes(p);
+
+    /* Last segment of the path may be owned by the user */
+    if ((d = strrchr(dir, '/')) != NULL)
+        *d = '\0';
+
+    while ((d=strrchr(dir, '/')) != NULL) {
+
+        /* Do not follow symlinks */
+        if (lstat(dir, &st) != 0)
+            goto error;
+
+        if (S_ISLNK(st.st_mode)) {
+            if (st.st_uid != 0) {
+                if (idata->flags & PAMNS_DEBUG)
+                    pam_syslog(idata->pamh, LOG_DEBUG,
+                            "Path deemed unsafe: Symlink %s should be owned by root", dir);
+                goto error;
+            }
+
+            /* Follow symlinks */
+            if (stat(dir, &st) != 0)
+                goto error;
+        }
+
+        if (!S_ISDIR(st.st_mode)) {
+                if (idata->flags & PAMNS_DEBUG)
+                    pam_syslog(idata->pamh, LOG_DEBUG,
+                        "Path deemed unsafe: %s is expected to be a directory", dir);
+            goto error;
+        }
+
+        if (st.st_uid != 0 ||
+            ((st.st_mode & (S_IWGRP|S_IWOTH)) && !(st.st_mode & S_ISVTX))) {
+                if (idata->flags & PAMNS_DEBUG)
+                    pam_syslog(idata->pamh, LOG_DEBUG,
+                        "Path deemed unsafe: %s should be owned by root, and not be writable by group or others", dir);
+            goto error;
+        }
+
+        *d = '\0';
+    }
+
+    free(p);
+    return 0;
+
+error:
+    free(p);
+    return -1;
+}
+
 /*
 * Check to see if there is a namespace initialization script in
 * the /etc/security directory. If such a script exists
@@ -1349,68 +1563,72 @@ static int inst_init(const struct polydir_s *polyptr, const char *ipath,
 	if ((polyptr->flags & POLYDIR_ISCRIPT) && polyptr->init_script)
 		init_script = polyptr->init_script;
 
-	if (access(init_script, F_OK) == 0) {
-		if (access(init_script, X_OK) < 0) {
-			if (idata->flags & PAMNS_DEBUG)
-				pam_syslog(idata->pamh, LOG_ERR,
-						"Namespace init script not executable");
-			return PAM_SESSION_ERR;
-		} else {
-			struct sigaction newsa, oldsa;
+	if (access(init_script, F_OK) != 0)
+		return PAM_SUCCESS;
 
-			memset(&newsa, '\0', sizeof(newsa));
-			newsa.sa_handler = SIG_DFL;
-			if (sigaction(SIGCHLD, &newsa, &oldsa) == -1) {
-				pam_syslog(idata->pamh, LOG_ERR, "failed to reset SIGCHLD handler");
-				return PAM_SESSION_ERR;
-			}
-
-			pid = fork();
-			if (pid == 0) {
-				static char *envp[] = { NULL };
-#ifdef WITH_SELINUX
-				if (idata->flags & PAMNS_SELINUX_ENABLED) {
-					if (setexeccon(NULL) < 0)
-						_exit(1);
-				}
-#endif
-				/* Pass maximum privs when we exec() */
-				if (setuid(geteuid()) < 0) {
-					/* ignore failures, they don't matter */
-				}
-
-				close_fds_pre_exec(idata);
-
-				if (execle(init_script, init_script,
-					polyptr->dir, ipath, newdir?"1":"0", idata->user, NULL, envp) < 0)
-					_exit(1);
-			} else if (pid > 0) {
-				while (((rc = waitpid(pid, &status, 0)) == (pid_t)-1) &&
-						(errno == EINTR));
-				if (rc == (pid_t)-1) {
-					pam_syslog(idata->pamh, LOG_ERR, "waitpid failed- %m");
-					rc = PAM_SESSION_ERR;
-					goto out;
-				}
-				if (!WIFEXITED(status) || WIFSIGNALED(status) > 0) {
-					pam_syslog(idata->pamh, LOG_ERR,
-							"Error initializing instance");
-					rc = PAM_SESSION_ERR;
-					goto out;
-				}
-			} else if (pid < 0) {
-				pam_syslog(idata->pamh, LOG_ERR,
-						"Cannot fork to run namespace init script, %m");
-				rc = PAM_SESSION_ERR;
-				goto out;
-			}
-			rc = PAM_SUCCESS;
-out:
-			(void) sigaction(SIGCHLD, &oldsa, NULL);
-			return rc;
-		}
+	if (access(init_script, X_OK) < 0) {
+		if (idata->flags & PAMNS_DEBUG)
+			pam_syslog(idata->pamh, LOG_ERR,
+					"Namespace init script not executable");
+		return PAM_SESSION_ERR;
 	}
-	return PAM_SUCCESS;
+
+	struct sigaction newsa, oldsa;
+
+	memset(&newsa, '\0', sizeof(newsa));
+	newsa.sa_handler = SIG_DFL;
+	if (sigaction(SIGCHLD, &newsa, &oldsa) == -1) {
+		pam_syslog(idata->pamh, LOG_ERR, "failed to reset SIGCHLD handler");
+		return PAM_SESSION_ERR;
+	}
+
+	pid = fork();
+	if (pid == 0) {
+		static char *envp[] = { NULL };
+#ifdef WITH_SELINUX
+		if (idata->flags & PAMNS_SELINUX_ENABLED) {
+			if (setexeccon(NULL) < 0)
+				_exit(1);
+		}
+#endif
+		/* Pass maximum privs when we exec() */
+		if (setuid(geteuid()) < 0) {
+			/* ignore failures, they don't matter */
+		}
+
+		close_fds_pre_exec(idata);
+
+		execle(init_script, init_script,
+		       polyptr->dir, ipath,
+		       newdir ? "1":"0", idata->user,
+		       (check_safe_path(polyptr->dir, idata) == -1) ? "0":"1",
+		       (check_safe_path(ipath, idata) == -1) ? "0":"1",
+		       NULL, envp);
+		_exit(1);
+	} else if (pid > 0) {
+		while (((rc = waitpid(pid, &status, 0)) == (pid_t)-1) &&
+				(errno == EINTR));
+		if (rc == (pid_t)-1) {
+			pam_syslog(idata->pamh, LOG_ERR, "waitpid failed- %m");
+			rc = PAM_SESSION_ERR;
+			goto out;
+		}
+		if (!WIFEXITED(status) || WIFSIGNALED(status) > 0) {
+			pam_syslog(idata->pamh, LOG_ERR,
+					"Error initializing instance");
+			rc = PAM_SESSION_ERR;
+			goto out;
+		}
+	} else if (pid < 0) {
+		pam_syslog(idata->pamh, LOG_ERR,
+				"Cannot fork to run namespace init script, %m");
+		rc = PAM_SESSION_ERR;
+		goto out;
+	}
+	rc = PAM_SUCCESS;
+out:
+	(void) sigaction(SIGCHLD, &oldsa, NULL);
+	return rc;
 }
 
 static int create_polydir(struct polydir_s *polyptr,
@@ -1460,14 +1678,16 @@ static int create_polydir(struct polydir_s *polyptr,
     }
 #endif
 
-    rc = protect_dir(dir, mode, 1, idata);
+    rc = secure_opendir(dir,
+            SECURE_OPENDIR_PROTECT | SECURE_OPENDIR_MKDIR | SECURE_OPENDIR_FULL_FD,
+            mode, idata);
     if (rc == -1) {
             pam_syslog(idata->pamh, LOG_ERR,
                        "Error creating directory %s: %m", dir);
 #ifdef WITH_SELINUX
             freecon(oldcon_raw);
 #endif
-            return PAM_SESSION_ERR;
+            return -1;
     }
 
 #ifdef WITH_SELINUX
@@ -1488,9 +1708,9 @@ static int create_polydir(struct polydir_s *polyptr,
 		pam_syslog(idata->pamh, LOG_ERR,
 			   "Error changing mode of directory %s: %m", dir);
                 close(rc);
-                umount(dir); /* undo the eventual protection bind mount */
-		rmdir(dir);
-		return PAM_SESSION_ERR;
+		secure_umount(dir); /* undo the eventual protection bind mount */
+		secure_try_rmdir(dir);
+		return -1;
 	}
     }
 
@@ -1508,41 +1728,37 @@ static int create_polydir(struct polydir_s *polyptr,
         pam_syslog(idata->pamh, LOG_ERR,
                    "Unable to change owner on directory %s: %m", dir);
         close(rc);
-        umount(dir); /* undo the eventual protection bind mount */
-	rmdir(dir);
-	return PAM_SESSION_ERR;
+	secure_umount(dir); /* undo the eventual protection bind mount */
+	secure_try_rmdir(dir);
+	return -1;
     }
 
-    close(rc);
-
     if (idata->flags & PAMNS_DEBUG)
 	pam_syslog(idata->pamh, LOG_DEBUG,
 	           "Polydir owner %u group %u", uid, gid);
 
-    return PAM_SUCCESS;
+    return rc;
 }
 
 /*
- * Create polyinstantiated instance directory (ipath).
+ * Create polyinstantiated instance directory.
+ * To protect against races, changes are done on a fd to the parent of the
+ * instance directory (dfd_iparent) and a relative path (polyptr->instname).
+ * The absolute path (polyptr->instance_absolute) is only updated when creating
+ * a tmpdir and used for logging purposes.
  */
 #ifdef WITH_SELINUX
-static int create_instance(struct polydir_s *polyptr, char *ipath, struct stat *statbuf,
-        const char *icontext, const char *ocontext,
-	struct instance_data *idata)
+static int create_instance(struct polydir_s *polyptr, int dfd_iparent,
+        struct stat *statbuf, const char *icontext, const char *ocontext,
+        struct instance_data *idata)
 #else
-static int create_instance(struct polydir_s *polyptr, char *ipath, struct stat *statbuf,
-	struct instance_data *idata)
+static int create_instance(struct polydir_s *polyptr, int dfd_iparent,
+        struct stat *statbuf, struct instance_data *idata)
 #endif
 {
     struct stat newstatbuf;
     int fd;
 
-    /*
-     * Check to make sure instance parent is valid.
-     */
-    if (check_inst_parent(ipath, idata))
-	return PAM_SESSION_ERR;
-
     /*
      * Create instance directory and set its security context to the context
      * returned by the security policy. Set its mode and ownership
@@ -1551,29 +1767,39 @@ static int create_instance(struct polydir_s *polyptr, char *ipath, struct stat *
      */
 
     if (polyptr->method == TMPDIR) {
-	if (mkdtemp(polyptr->instance_prefix) == NULL) {
-            pam_syslog(idata->pamh, LOG_ERR, "Error creating temporary instance %s, %m",
-			polyptr->instance_prefix);
-	    polyptr->method = NONE; /* do not clean up! */
-	    return PAM_SESSION_ERR;
-	}
-	/* copy the actual directory name to ipath */
-	strcpy(ipath, polyptr->instance_prefix);
-    } else if (mkdir(ipath, S_IRUSR) < 0) {
+        char s_path[PATH_MAX];
+        /*
+         * Create the template for mkdtemp() as a magic link based on
+         * our existing fd to avoid symlink attacks and races.
+         */
+        if (pam_sprintf(s_path, "/proc/self/fd/%d/%s", dfd_iparent, polyptr->instname) < 0
+            || mkdtemp(s_path) == NULL) {
+            pam_syslog(idata->pamh, LOG_ERR,
+                       "Error creating temporary instance dir %s, %m",
+                       polyptr->instance_absolute);
+            polyptr->method = NONE; /* do not clean up! */
+            return PAM_SESSION_ERR;
+        }
+
+        /* Copy the actual directory name to polyptr->instname */
+        strcpy(polyptr->instname, base_name(s_path));
+    } else if (mkdirat(dfd_iparent, polyptr->instname, S_IRUSR) < 0) {
         if (errno == EEXIST)
             return PAM_IGNORE;
         else {
             pam_syslog(idata->pamh, LOG_ERR, "Error creating %s, %m",
-			ipath);
+                       polyptr->instance_absolute);
             return PAM_SESSION_ERR;
         }
     }
 
-    /* Open a descriptor to it to prevent races */
-    fd = open(ipath, O_DIRECTORY | O_RDONLY);
+    /* Open a descriptor to prevent races, based on our existing fd. */
+    fd = openat(dfd_iparent, polyptr->instname,
+            O_RDONLY | O_DIRECTORY | O_NOFOLLOW | O_CLOEXEC);
     if (fd < 0) {
-	pam_syslog(idata->pamh, LOG_ERR, "Error opening %s, %m", ipath);
-	rmdir(ipath);
+	pam_syslog(idata->pamh, LOG_ERR, "Error opening %s, %m",
+                polyptr->instance_absolute);
+	unlinkat(dfd_iparent, polyptr->instname, AT_REMOVEDIR);
 	return PAM_SESSION_ERR;
     }
 #ifdef WITH_SELINUX
@@ -1583,17 +1809,19 @@ static int create_instance(struct polydir_s *polyptr, char *ipath, struct stat *
         if (icontext) {
             if (fsetfilecon(fd, icontext) < 0) {
                 pam_syslog(idata->pamh, LOG_ERR,
-			"Error setting context of %s to %s", ipath, icontext);
+			"Error setting context of %s to %s",
+                        polyptr->instance_absolute, icontext);
                 close(fd);
-		rmdir(ipath);
+                unlinkat(dfd_iparent, polyptr->instname, AT_REMOVEDIR);
                 return PAM_SESSION_ERR;
             }
         } else {
             if (fsetfilecon(fd, ocontext) < 0) {
                 pam_syslog(idata->pamh, LOG_ERR,
-			"Error setting context of %s to %s", ipath, ocontext);
+			"Error setting context of %s to %s",
+                        polyptr->instance_absolute, ocontext);
 		close(fd);
-		rmdir(ipath);
+                unlinkat(dfd_iparent, polyptr->instname, AT_REMOVEDIR);
                 return PAM_SESSION_ERR;
             }
         }
@@ -1601,9 +1829,9 @@ static int create_instance(struct polydir_s *polyptr, char *ipath, struct stat *
 #endif
     if (fstat(fd, &newstatbuf) < 0) {
         pam_syslog(idata->pamh, LOG_ERR, "Error stating %s, %m",
-		ipath);
+		polyptr->instance_absolute);
 	close(fd);
-	rmdir(ipath);
+        unlinkat(dfd_iparent, polyptr->instname, AT_REMOVEDIR);
         return PAM_SESSION_ERR;
     }
     if (newstatbuf.st_uid != statbuf->st_uid ||
@@ -1611,17 +1839,17 @@ static int create_instance(struct polydir_s *polyptr, char *ipath, struct stat *
         if (fchown(fd, statbuf->st_uid, statbuf->st_gid) < 0) {
             pam_syslog(idata->pamh, LOG_ERR,
 			"Error changing owner for %s, %m",
-			ipath);
+			polyptr->instance_absolute);
 	    close(fd);
-	    rmdir(ipath);
+            unlinkat(dfd_iparent, polyptr->instname, AT_REMOVEDIR);
             return PAM_SESSION_ERR;
         }
     }
     if (fchmod(fd, statbuf->st_mode & 07777) < 0) {
         pam_syslog(idata->pamh, LOG_ERR, "Error changing mode for %s, %m",
-			ipath);
+			polyptr->instance_absolute);
 	close(fd);
-	rmdir(ipath);
+        unlinkat(dfd_iparent, polyptr->instname, AT_REMOVEDIR);
         return PAM_SESSION_ERR;
     }
     close(fd);
@@ -1640,9 +1868,12 @@ static int ns_setup(struct polydir_s *polyptr,
 	struct instance_data *idata)
 {
     int retval;
+    int dfd_iparent = -1;
+    int dfd_ipath = -1;
+    int dfd_pptrdir = -1;
     int newdir = 1;
-    char *inst_dir = NULL;
-    char *instname = NULL;
+    char s_ipath[MAGIC_LNK_FD_SIZE];
+    char s_pptrdir[MAGIC_LNK_FD_SIZE];
     struct stat statbuf;
 #ifdef WITH_SELINUX
     char *instcontext = NULL, *origcontext = NULL;
@@ -1652,39 +1883,48 @@ static int ns_setup(struct polydir_s *polyptr,
         pam_syslog(idata->pamh, LOG_DEBUG,
                "Set namespace for directory %s", polyptr->dir);
 
-    retval = protect_dir(polyptr->dir, 0, 0, idata);
+    dfd_pptrdir = secure_opendir(polyptr->dir, SECURE_OPENDIR_PROTECT, 0, idata);
 
-    if (retval < 0 && errno != ENOENT) {
-	pam_syslog(idata->pamh, LOG_ERR, "Polydir %s access error: %m",
-		polyptr->dir);
-	return PAM_SESSION_ERR;
-    }
-
-    if (retval < 0) {
-	if ((polyptr->flags & POLYDIR_CREATE) &&
-		create_polydir(polyptr, idata) != PAM_SUCCESS)
-		return PAM_SESSION_ERR;
-    } else {
-	close(retval);
+    if (dfd_pptrdir < 0) {
+        if (errno != ENOENT || !(polyptr->flags & POLYDIR_CREATE)) {
+            pam_syslog(idata->pamh, LOG_ERR, "Polydir %s access error: %m",
+                    polyptr->dir);
+            return PAM_SESSION_ERR;
+        }
+        dfd_pptrdir = create_polydir(polyptr, idata);
+        if (dfd_pptrdir < 0)
+            return PAM_SESSION_ERR;
     }
 
     if (polyptr->method == TMPFS) {
-	if (mount("tmpfs", polyptr->dir, "tmpfs", polyptr->mount_flags, polyptr->mount_opts) < 0) {
-	    pam_syslog(idata->pamh, LOG_ERR, "Error mounting tmpfs on %s, %m",
-		polyptr->dir);
-            return PAM_SESSION_ERR;
-	}
+        /*
+         * There is no function mount() that operate on a fd, so instead, we
+         * get the magic link corresponding to the fd and give it to mount().
+         * This protects against potential races exploitable by an unpriv user.
+         */
+        if (pam_sprintf(s_pptrdir, "/proc/self/fd/%d", dfd_pptrdir) < 0) {
+            pam_syslog(idata->pamh, LOG_ERR, "Error pam_sprintf s_pptrdir");
+            goto error_out;
+        }
 
-	if (polyptr->flags & POLYDIR_NOINIT)
-	    return PAM_SUCCESS;
+        if (mount("tmpfs", s_pptrdir, "tmpfs", polyptr->mount_flags, polyptr->mount_opts) < 0) {
+            pam_syslog(idata->pamh, LOG_ERR, "Error mounting tmpfs on %s, %m",
+                       polyptr->dir);
+            goto error_out;
+        }
 
-	return inst_init(polyptr, "tmpfs", idata, 1);
+        if (polyptr->flags & POLYDIR_NOINIT) {
+            retval = PAM_SUCCESS;
+            goto cleanup;
+        }
+
+        retval = inst_init(polyptr, "tmpfs", idata, 1);
+        goto cleanup;
     }
 
-    if (stat(polyptr->dir, &statbuf) < 0) {
-	pam_syslog(idata->pamh, LOG_ERR, "Error stating %s: %m",
-		polyptr->dir);
-        return PAM_SESSION_ERR;
+    if (fstat(dfd_pptrdir, &statbuf) < 0) {
+        pam_syslog(idata->pamh, LOG_ERR, "Error stating %s: %m", polyptr->dir);
+        goto error_out;
     }
 
     /*
@@ -1693,15 +1933,16 @@ static int ns_setup(struct polydir_s *polyptr,
      * security policy.
      */
 #ifdef WITH_SELINUX
-    retval = poly_name(polyptr, &instname, &instcontext,
-			&origcontext, idata);
+    retval = poly_name(polyptr, &instcontext, &origcontext, idata);
 #else
-    retval = poly_name(polyptr, &instname, idata);
+    retval = poly_name(polyptr, idata);
 #endif
 
     if (retval != PAM_SUCCESS) {
-	if (retval != PAM_IGNORE)
+	if (retval != PAM_IGNORE) {
 		pam_syslog(idata->pamh, LOG_ERR, "Error getting instance name");
+                goto error_out;
+        }
         goto cleanup;
     } else {
 #ifdef WITH_SELINUX
@@ -1712,22 +1953,33 @@ static int ns_setup(struct polydir_s *polyptr,
 #endif
     }
 
-    if (asprintf(&inst_dir, "%s%s", polyptr->instance_prefix, instname) < 0)
-	goto error_out;
-
-    if (idata->flags & PAMNS_DEBUG)
-        pam_syslog(idata->pamh, LOG_DEBUG, "instance_dir %s",
-		inst_dir);
+    /*
+     * Gets a fd in a secure manner (we may be operating on a path under
+     * user control), and check it's compliant.
+     * Then, we should *always* operate on *this* fd and a relative path
+     * to be protected against race conditions.
+     */
+    dfd_iparent = secure_opendir(polyptr->instance_parent,
+            SECURE_OPENDIR_PROTECT | SECURE_OPENDIR_MKDIR, 0, idata);
+    if (dfd_iparent == -1) {
+	pam_syslog(idata->pamh, LOG_ERR,
+                "polyptr->instance_parent %s access error",
+                polyptr->instance_parent);
+        goto error_out;
+    }
+    if (check_inst_parent(dfd_iparent, idata)) {
+        goto error_out;
+    }
 
     /*
      * Create instance directory with appropriate security
      * contexts, owner, group and mode bits.
      */
 #ifdef WITH_SELINUX
-    retval = create_instance(polyptr, inst_dir, &statbuf, instcontext,
-			 origcontext, idata);
+    retval = create_instance(polyptr, dfd_iparent, &statbuf, instcontext,
+                             origcontext, idata);
 #else
-    retval = create_instance(polyptr, inst_dir, &statbuf, idata);
+    retval = create_instance(polyptr, dfd_iparent, &statbuf, idata);
 #endif
 
     if (retval == PAM_IGNORE) {
@@ -1739,19 +1991,48 @@ static int ns_setup(struct polydir_s *polyptr,
         goto error_out;
     }
 
+    /*
+     * Instead of getting a new secure fd, we reuse the fd opened on directory
+     * polyptr->instance_parent to ensure we are working on the same dir as
+     * previously, and thus ensure that previous checks (e.g. check_inst_parent())
+     * are still relevant.
+     */
+    dfd_ipath = openat(dfd_iparent, polyptr->instname,
+            O_PATH | O_DIRECTORY | O_NOFOLLOW | O_CLOEXEC);
+    if (dfd_ipath == -1) {
+        pam_syslog(idata->pamh, LOG_ERR, "Error openat on %s, %m",
+                polyptr->instname);
+        goto error_out;
+    }
+
+    if (pam_sprintf(s_ipath, "/proc/self/fd/%d", dfd_ipath) < 0) {
+        pam_syslog(idata->pamh, LOG_ERR, "Error pam_sprintf s_ipath");
+        goto error_out;
+    }
+
+    if (pam_sprintf(s_pptrdir, "/proc/self/fd/%d", dfd_pptrdir) < 0) {
+        pam_syslog(idata->pamh, LOG_ERR, "Error pam_sprintf s_pptrdir");
+        goto error_out;
+    }
+
     /*
      * Bind mount instance directory on top of the polyinstantiated
      * directory to provide an instance of polyinstantiated directory
      * based on polyinstantiated method.
+     *
+     * Operates on magic links created from two fd obtained securely
+     * to protect against race conditions and symlink attacks. Indeed,
+     * the source and destination can be in a user controled path.
      */
-    if (mount(inst_dir, polyptr->dir, NULL, MS_BIND, NULL) < 0) {
-        pam_syslog(idata->pamh, LOG_ERR, "Error mounting %s on %s, %m",
-                   inst_dir, polyptr->dir);
+    if(mount(s_ipath, s_pptrdir, NULL, MS_BIND, NULL) < 0) {
+        pam_syslog(idata->pamh, LOG_ERR,
+                "Error mounting %s on %s (%s on %s), %m",
+                   s_ipath, s_pptrdir, polyptr->instance_absolute, polyptr->dir);
         goto error_out;
     }
 
     if (!(polyptr->flags & POLYDIR_NOINIT))
-	retval = inst_init(polyptr, inst_dir, idata, newdir);
+	retval = inst_init(polyptr, polyptr->instance_absolute, idata, newdir);
 
     goto cleanup;
 
@@ -1763,8 +2044,12 @@ error_out:
     retval = PAM_SESSION_ERR;
 
 cleanup:
-    free(inst_dir);
-    free(instname);
+    if (dfd_iparent != -1)
+        close(dfd_iparent);
+    if (dfd_ipath != -1)
+        close(dfd_ipath);
+    if (dfd_pptrdir != -1)
+        close(dfd_pptrdir);
 #ifdef WITH_SELINUX
     freecon(instcontext);
     freecon(origcontext);
@@ -1803,6 +2088,7 @@ static int cleanup_tmpdirs(struct instance_data *idata)
 {
     struct polydir_s *pptr;
     pid_t rc, pid;
+    int dfd = -1;
     struct sigaction newsa, oldsa;
     int status;
 
@@ -1814,7 +2100,17 @@ static int cleanup_tmpdirs(struct instance_data *idata)
     }
 
     for (pptr = idata->polydirs_ptr; pptr; pptr = pptr->next) {
-	if (pptr->method == TMPDIR && access(pptr->instance_prefix, F_OK) == 0) {
+	if (pptr->method == TMPDIR) {
+
+            dfd = secure_opendir_stateless(pptr->instance_parent);
+            if (dfd == -1)
+                continue;
+
+            if (faccessat(dfd, pptr->instname, F_OK, AT_SYMLINK_NOFOLLOW) != 0) {
+                close(dfd);
+                continue;
+            }
+
 	    pid = fork();
 	    if (pid == 0) {
 		static char *envp[] = { NULL };
@@ -1824,10 +2120,21 @@ static int cleanup_tmpdirs(struct instance_data *idata)
 			_exit(1);
 		}
 #endif
+                if (fchdir(dfd) == -1) {
+                    pam_syslog(idata->pamh, LOG_ERR, "Failed fchdir to %s: %m",
+                            pptr->instance_absolute);
+                    _exit(1);
+                }
+
 		close_fds_pre_exec(idata);
-		if (execle("/bin/rm", "/bin/rm", "-rf", pptr->instance_prefix, NULL, envp) < 0)
-			_exit(1);
+
+		execle("/bin/rm", "/bin/rm", "-rf", pptr->instname, NULL, envp);
+		_exit(1);
 	    } else if (pid > 0) {
+
+                if (dfd != -1)
+                    close(dfd);
+
 		while (((rc = waitpid(pid, &status, 0)) == (pid_t)-1) &&
 		    (errno == EINTR));
 		if (rc == (pid_t)-1) {
@@ -1840,6 +2147,10 @@ static int cleanup_tmpdirs(struct instance_data *idata)
 			"Error removing %s", pptr->instance_prefix);
 		}
 	    } else if (pid < 0) {
+
+                if (dfd != -1)
+                    close(dfd);
+
 		pam_syslog(idata->pamh, LOG_ERR,
 			"Cannot fork to cleanup temporary directory, %m");
 		rc = PAM_SESSION_ERR;
@@ -1863,6 +2174,7 @@ out:
 static int setup_namespace(struct instance_data *idata, enum unmnt_op unmnt)
 {
     int retval = 0, need_poly = 0, changing_dir = 0;
+    int dfd = -1;
     char *cptr, *fptr, poly_parent[PATH_MAX];
     struct polydir_s *pptr;
 
@@ -1978,13 +2290,21 @@ static int setup_namespace(struct instance_data *idata, enum unmnt_op unmnt)
 			strcpy(poly_parent, "/");
 		    else if (cptr)
 			*cptr = '\0';
-                    if (chdir(poly_parent) < 0) {
+
+                    dfd = secure_opendir_stateless(poly_parent);
+                    if (dfd == -1) {
                         pam_syslog(idata->pamh, LOG_ERR,
-				"Can't chdir to %s, %m", poly_parent);
+                            "Failed opening %s to fchdir: %m", poly_parent);
                     }
+                    else if (fchdir(dfd) == -1) {
+                        pam_syslog(idata->pamh, LOG_ERR,
+                            "Failed fchdir to %s: %m", poly_parent);
+                    }
+                    if (dfd != -1)
+                        close(dfd);
                 }
 
-                if (umount(pptr->rdir) < 0) {
+            if (secure_umount(pptr->rdir) < 0) {
 		    int saved_errno = errno;
 		    pam_syslog(idata->pamh, LOG_ERR, "Unmount of %s failed, %m",
 			pptr->rdir);
@@ -2054,7 +2374,7 @@ static int orig_namespace(struct instance_data *idata)
 			"Unmounting instance dir for user %d & dir %s",
                        idata->uid, pptr->dir);
 
-            if (umount(pptr->dir) < 0) {
+            if (secure_umount(pptr->dir) < 0) {
                 pam_syslog(idata->pamh, LOG_ERR, "Unmount of %s failed, %m",
                        pptr->dir);
                 return PAM_SESSION_ERR;
diff --git a/modules/pam_namespace/pam_namespace.h b/modules/pam_namespace/pam_namespace.h
index 1799938..8a7a66b 100644
--- a/modules/pam_namespace/pam_namespace.h
+++ b/modules/pam_namespace/pam_namespace.h
@@ -44,21 +44,17 @@
 #include <stdlib.h>
 #include <errno.h>
 #include <syslog.h>
-#include <dlfcn.h>
-#include <stdarg.h>
 #include <pwd.h>
 #include <grp.h>
 #include <limits.h>
 #include <sys/types.h>
 #include <sys/stat.h>
-#include <sys/resource.h>
 #include <sys/mount.h>
 #include <sys/wait.h>
 #include <libgen.h>
 #include <fcntl.h>
 #include <sched.h>
 #include <glob.h>
-#include <locale.h>
 #include "security/pam_modules.h"
 #include "security/pam_modutil.h"
 #include "security/pam_ext.h"
@@ -126,6 +122,13 @@
 #define NAMESPACE_POLYDIR_DATA "pam_namespace:polydir_data"
 #define NAMESPACE_PROTECT_DATA "pam_namespace:protect_data"
 
+/*
+ * Operation mode for function secure_opendir()
+ */
+#define SECURE_OPENDIR_PROTECT     0x00000001
+#define SECURE_OPENDIR_MKDIR       0x00000002
+#define SECURE_OPENDIR_FULL_FD     0x00000004
+
 /*
  * Polyinstantiation method options, based on user, security context
  * or both
@@ -163,6 +166,9 @@ struct polydir_s {
     char dir[PATH_MAX];    	       	/* directory to polyinstantiate */
     char rdir[PATH_MAX];    	       	/* directory to unmount (based on RUSER) */
     char instance_prefix[PATH_MAX];	/* prefix for instance dir path name */
+    char instance_absolute[PATH_MAX];	/* absolute path to the instance dir (instance_parent + instname) */
+    char instance_parent[PATH_MAX];	/* parent dir of the instance dir */
+    char *instname;			/* last segment of the path to the instance dir */
     enum polymethod method;		/* method used to polyinstantiate */
     unsigned int num_uids;		/* number of override uids */
     uid_t *uid;				/* list of override uids */