From: Andy Lutomirski <luto@amacapital.net>
Date: Wed, 8 Oct 2014 12:37:46 -0700
Subject: [PATCH] fs: Add a missing permission check to do_umount

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.

Cc: stable@vger.kernel.org
Signed-off-by: Andy Lutomirski <luto@amacapital.net>
---
 fs/namespace.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/namespace.c b/fs/namespace.c
index 74647c2fe69c..550dbff08677 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1356,6 +1356,8 @@ 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);
-- 
1.9.3