mount.cifs: don't allow it to be run as setuid root program

mount.cifs has been the subject of several "security" fire drills due to
distributions installing it as a setuid root program. This program has
not been properly audited for security and the Samba team highly
recommends that it not be installed as a setuid root program at this
time.

To make that abundantly clear, this patch forcibly disables the ability
for mount.cifs to run as a setuid root program. People are welcome to
trivially patch this out, but they do so at their own peril.

A security audit and redesign of this program is in progress and we hope
that we'll be able to remove this in the near future.

Signed-off-by: Jeff Layton <jlayton@redhat.com>

The last 5 patches address bug #6853 (mount.cifs race that allows user to
replace mountpoint with a symlink).
(cherry picked from commit f94a377fb58f7b104aa633236f3391c9af6a7b12)

1 files changed, 38 insertions, 1 deletions

diff --git a/source3/client/mount.cifs.c b/source3/client/mount.cifs.c
index 47d88fd39ad..92dd68f77db 100644
--- a/source3/client/mount.cifs.c
+++ b/source3/client/mount.cifs.c
@@ -43,7 +43,7 @@
 #include "mount.h"
 
 #define MOUNT_CIFS_VERSION_MAJOR "1"
-#define MOUNT_CIFS_VERSION_MINOR "13"
+#define MOUNT_CIFS_VERSION_MINOR "14"
 
 #ifndef MOUNT_CIFS_VENDOR_SUFFIX
  #ifdef _SAMBA_BUILD_
@@ -89,6 +89,17 @@
 #define MAX_ADDRESS_LEN INET6_ADDRSTRLEN
 
 /*
+ * mount.cifs has been the subject of many "security" bugs that have arisen
+ * because of users and distributions installing it as a setuid root program.
+ * mount.cifs has not been audited for security. Thus, we strongly recommend
+ * that it not be installed setuid root. To make that abundantly clear,
+ * mount.cifs now check whether it's running setuid root and exit with an
+ * error if it is. If you wish to disable this check, then set the following
+ * #define to 1, but please realize that you do so at your own peril.
+ */
+#define CIFS_DISABLE_SETUID_CHECK 0
+
+/*
  * By default, mount.cifs follows the conventions set forth by /bin/mount
  * for user mounts. That is, it requires that the mount be listed in
  * /etc/fstab with the "user" option when run as an unprivileged user and
@@ -213,6 +224,29 @@ check_mountpoint(const char *progname, char *mountpoint)
 	return 0;
 }
 
+#if CIFS_DISABLE_SETUID_CHECK
+static int
+check_setuid(void)
+{
+	return 0;
+}
+#else /* CIFS_DISABLE_SETUID_CHECK */
+static int
+check_setuid(void)
+{
+	if (getuid() && !geteuid()) {
+		printf("This mount.cifs program has been built with the "
+			"ability to run as a setuid root program disabled.\n"
+			"mount.cifs has not been well audited for security "
+			"holes. Therefore the Samba team does not recommend "
+			"installing it as a setuid root program.\n");
+		return 1;
+	}
+
+	return 0;
+}
+#endif /* CIFS_DISABLE_SETUID_CHECK */
+
 #if CIFS_LEGACY_SETUID_CHECK
 static int
 check_fstab(const char *progname, char *mountpoint, char *devname,
@@ -1192,6 +1226,9 @@ int main(int argc, char ** argv)
 	struct sockaddr_in6 *addr6;
 	FILE * pmntfile;
 
+	if (check_setuid())
+		return EX_USAGE;
+
 	/* setlocale(LC_ALL, "");
 	bindtextdomain(PACKAGE, LOCALEDIR);
 	textdomain(PACKAGE); */