fs: Add a missing permission check to do_umount

commit a1480dcc3c706e309a88884723446f2e84fedd5b upstream.

Accessing do_remount_sb should require global CAP_SYS_ADMIN, but
only one of the two call sites was appropriately protected.

Fixes CVE-2014-7975.

Signed-off-by: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/namespace.c b/fs/namespace.c
index 00409ad..7f6a934 100644 (file)
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1274,6 +1274,8 @@ static int do_umount(struct mount *mnt, int flags)
                 * Special case for "unmounting" root ...
                 * we just try to remount it readonly.
                 */
+               if (!capable(CAP_SYS_ADMIN))
+                       return -EPERM;
                down_write(&sb->s_umount);
                if (!(sb->s_flags & MS_RDONLY))
                        retval = do_remount_sb(sb, MS_RDONLY, NULL, 0);