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From: Tavis Ormandy <taviso@google.com>
Date: Thu, 22 Aug 2013 10:59:36 -0700
Subject: Implement privmode, part 1
Origin: http://article.gmane.org/gmane.comp.security.oss.general/10969
---
src/dash.1 | 16 ++++++++++------
src/main.c | 17 +++++++++++++++++
src/options.c | 2 ++
src/options.h | 7 ++++---
src/var.c | 29 +++++++++++++++++++++++------
src/var.h | 1 +
6 files changed, 57 insertions(+), 15 deletions(-)
diff --git a/src/dash.1 b/src/dash.1
index b286f79..6c62245 100644
--- a/src/dash.1
+++ b/src/dash.1
@@ -41,8 +41,8 @@
.Sh SYNOPSIS
.Nm
.Bk -words
-.Op Fl aCefnuvxIimqVEb
-.Op Cm +aCefnuvxIimqVEb
+.Op Fl aCefnuvxIimqVEbp
+.Op Cm +aCefnuvxIimqVEbp
.Ek
.Bk -words
.Op Fl o Ar option_name
@@ -54,8 +54,8 @@
.Nm
.Fl c
.Bk -words
-.Op Fl aCefnuvxIimqVEb
-.Op Cm +aCefnuvxIimqVEb
+.Op Fl aCefnuvxIimqVEbp
+.Op Cm +aCefnuvxIimqVEbp
.Ek
.Bk -words
.Op Fl o Ar option_name
@@ -68,8 +68,8 @@
.Nm
.Fl s
.Bk -words
-.Op Fl aCefnuvxIimqVEb
-.Op Cm +aCefnuvxIimqVEb
+.Op Fl aCefnuvxIimqVEbp
+.Op Cm +aCefnuvxIimqVEbp
.Ek
.Bk -words
.Op Fl o Ar option_name
@@ -257,6 +257,10 @@ if it has been set).
.It Fl b Em notify
Enable asynchronous notification of background job completion.
(UNIMPLEMENTED for 4.4alpha)
+.It Fl p Em nopriv
+Do not attempt to reset effective uid if it does not match uid. This is not set
+by default to help avoid incorrect usage by setuid root programs via system(3) or
+popen(3).
.El
.Ss Lexical Structure
The shell reads input in terms of lines from a file and breaks it up into
diff --git a/src/main.c b/src/main.c
index 12dfc6e..83f0514 100644
--- a/src/main.c
+++ b/src/main.c
@@ -93,11 +93,16 @@ main(int argc, char **argv)
volatile int state;
struct stackmark smark;
int login;
+ uid_t uid;
+ gid_t gid;
#ifdef __GLIBC__
dash_errno = __errno_location();
#endif
+ uid = getuid();
+ gid = getgid();
+
#if PROFILE
monitor(4, etext, profile_buf, sizeof profile_buf, 50);
#endif
@@ -146,6 +151,18 @@ main(int argc, char **argv)
init();
setstackmark(&smark);
login = procargs(argc, argv);
+
+ /*
+ * To limit bogus system(3) or popen(3) calls in setuid binaries, require
+ * -p flag to work in this situation.
+ */
+ if (!pflag && (uid != geteuid() || gid != getegid())) {
+ setuid(uid);
+ setgid(gid);
+ /* PS1 might need to be changed accordingly. */
+ choose_ps1();
+ }
+
if (login) {
state = 1;
read_profile("/etc/profile");
diff --git a/src/options.c b/src/options.c
index a46c23b..48502bb 100644
--- a/src/options.c
+++ b/src/options.c
@@ -79,6 +79,7 @@ static const char *const optnames[NOPTS] = {
"allexport",
"notify",
"nounset",
+ "nopriv",
"nolog",
"debug",
};
@@ -99,6 +100,7 @@ const char optletters[NOPTS] = {
'a',
'b',
'u',
+ 'p',
0,
0,
};
diff --git a/src/options.h b/src/options.h
index 975fe33..9e90947 100644
--- a/src/options.h
+++ b/src/options.h
@@ -59,10 +59,11 @@ struct shparam {
#define aflag optlist[12]
#define bflag optlist[13]
#define uflag optlist[14]
-#define nolog optlist[15]
-#define debug optlist[16]
+#define pflag optlist[15]
+#define nolog optlist[16]
+#define debug optlist[17]
-#define NOPTS 17
+#define NOPTS 18
extern const char optletters[NOPTS];
extern char optlist[NOPTS];
diff --git a/src/var.c b/src/var.c
index 0d7e1db..35334bc 100644
--- a/src/var.c
+++ b/src/var.c
@@ -81,6 +81,9 @@ MKINIT char defoptindvar[] = "OPTIND=1";
int lineno;
char linenovar[sizeof("LINENO=")+sizeof(int)*CHAR_BIT/3+1] = "LINENO=";
+const char defps1[] = "PS1=$ ";
+const char rootps1[] = "PS1=# ";
+
/* Some macros in var.h depend on the order, add new variables to the end. */
struct var varinit[] = {
#if ATTY
@@ -90,7 +93,7 @@ struct var varinit[] = {
{ 0, VSTRFIXED|VTEXTFIXED|VUNSET, "MAIL\0", changemail },
{ 0, VSTRFIXED|VTEXTFIXED|VUNSET, "MAILPATH\0", changemail },
{ 0, VSTRFIXED|VTEXTFIXED, defpathvar, changepath },
- { 0, VSTRFIXED|VTEXTFIXED, "PS1=$ ", 0 },
+ { 0, VSTRFIXED|VTEXTFIXED, defps1, 0 },
{ 0, VSTRFIXED|VTEXTFIXED, "PS2=> ", 0 },
{ 0, VSTRFIXED|VTEXTFIXED, "PS4=+ ", 0 },
{ 0, VSTRFIXED|VTEXTFIXED, defoptindvar, getoptsreset },
@@ -174,11 +177,25 @@ initvar(void)
vp->next = *vpp;
*vpp = vp;
} while (++vp < end);
- /*
- * PS1 depends on uid
- */
- if (!geteuid())
- vps1.text = "PS1=# ";
+
+ choose_ps1();
+}
+
+/*
+ * Modify PS1 to reflect uid, unless an exported var exists.
+ */
+
+void
+choose_ps1(void)
+{
+ if (vps1.flags & VEXPORT)
+ return;
+
+ if (!geteuid()) {
+ vps1.text = rootps1;
+ } else {
+ vps1.text = defps1;
+ }
}
/*
diff --git a/src/var.h b/src/var.h
index cd0477f..6642b22 100644
--- a/src/var.h
+++ b/src/var.h
@@ -135,6 +135,7 @@ extern char linenovar[];
#define mpathset() ((vmpath.flags & VUNSET) == 0)
void initvar(void);
+void choose_ps1(void);
struct var *setvar(const char *name, const char *val, int flags);
intmax_t setvarint(const char *, intmax_t, int);
struct var *setvareq(char *s, int flags);
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