Description: Drop root privileges after opening savefile
Forwarded: no
Bug-Debian: https://bugs.debian.org/935112
Origin: https://src.fedoraproject.org/rpms/tcpdump/raw/master/f/0003-Drop-root-priviledges-before-opening-first-savefile-.patch
---
 tcpdump.1.in |  7 ++++++-
 tcpdump.c    | 30 ++++++++++++++++++++++++++++++
 2 files changed, 36 insertions(+), 1 deletion(-)

--- a/tcpdump.1.in
+++ b/tcpdump.1.in
@@ -267,6 +267,9 @@
 flag, with a number after it, starting at 1 and continuing upward.
 The units of \fIfile_size\fP are millions of bytes (1,000,000 bytes,
 not 1,048,576 bytes).
+
+Note that when used with \fB\-Z\fR option (enabled by default), privileges
+are dropped before opening first savefile.
 .TP
 .B \-d
 Dump the compiled packet-matching code in a human readable form to
@@ -962,12 +965,14 @@
 If
 .I tcpdump
 is running as root, after opening the capture device or input savefile,
-but before opening any savefiles for output, change the user ID to
+change the user ID to
 .I user
 and the group ID to the primary group of
 .IR user .
 .IP
-This behavior can also be enabled by default at compile time.
+This behavior is enabled by default (\fB\-Z tcpdump\fR), and can
+be disabled by \fB\-Z root\fR.
+
 .IP "\fI expression\fP"
 .RS
 selects which packets will be dumped.
--- a/tcpdump.c
+++ b/tcpdump.c
@@ -1492,6 +1492,7 @@
 	cap_rights_t rights;
 	int cansandbox;
 #endif	/* HAVE_CAPSICUM */
+	int chown_flag = 0;
 	int Oflag = 1;			/* run filter code optimizer */
 	int yflag_dlt = -1;
 	const char *yflag_dlt_name = NULL;
@@ -2320,6 +2321,19 @@
 		}
 		capng_apply(CAPNG_SELECT_BOTH);
 #endif /* HAVE_LIBCAP_NG */
+	/* If user is running tcpdump as root and wants to write to the savefile,
+	 * we will check if -C is set and if it is, we will drop root
+	 * privileges right away and consequent call to>pcap_dump_open()
+	 * will most likely fail for the first file. If -C flag is not set we
+	 * will create file as root then change ownership of file to proper
+	 * user(default tcpdump) and drop root privileges.
+	 */
+	if (WFileName)
+		if (Cflag && (username || chroot_dir))
+			droproot(username, chroot_dir);
+		else
+			chown_flag = 1;
+	else
 		if (username || chroot_dir)
 			droproot(username, chroot_dir);
 
@@ -2377,6 +2391,22 @@
 #endif /* HAVE_LIBCAP_NG */
 		if (pdd == NULL)
 			error("%s", pcap_geterr(pd));
+
+		/* Change ownership of file and drop root privileges */
+		if (chown_flag) {
+			struct passwd *pwd;
+
+			pwd = getpwnam(username);
+			if (!pwd)
+				error("Couldn't find user '%s'", username);
+
+			if (strcmp(WFileName, "-") && chown(dumpinfo.CurrentFileName, pwd->pw_uid, pwd->pw_gid) < 0)
+				error("Couldn't change ownership of savefile");
+
+			if (username || chroot_dir)
+				droproot(username, chroot_dir);
+	    }
+
 #ifdef HAVE_CAPSICUM
 		set_dumper_capsicum_rights(pdd);
 #endif