From 7a46cba4af686866672ec1de1467998a270bec29 Mon Sep 17 00:00:00 2001 From: "Eric W. Biederman" Date: Mon, 28 Jul 2014 16:26:53 -0700 Subject: mnt: Only change user settable mount flags in remount commit a6138db815df5ee542d848318e5dae681590fccd upstream. Kenton Varda discovered that by remounting a read-only bind mount read-only in a user namespace the MNT_LOCK_READONLY bit would be cleared, allowing an unprivileged user to the remount a read-only mount read-write. Correct this by replacing the mask of mount flags to preserve with a mask of mount flags that may be changed, and preserve all others. This ensures that any future bugs with this mask and remount will fail in an easy to detect way where new mount flags simply won't change. Change-Id: I8ab8bda03a14b9b43e78f1dc6c818bbec048e986 Acked-by: Serge E. Hallyn Signed-off-by: "Eric W. Biederman" Cc: Francis Moreau Signed-off-by: Zefan Li --- fs/namespace.c | 2 +- include/linux/mount.h | 4 +++- 2 files changed, 4 insertions(+), 2 deletions(-) diff --git a/fs/namespace.c b/fs/namespace.c index b3d8f51..912d273 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -1842,7 +1842,7 @@ static int do_remount(struct path *path, int flags, int mnt_flags, err = do_remount_sb(sb, flags, data, 0); if (!err) { br_write_lock(vfsmount_lock); - mnt_flags |= path->mnt->mnt_flags & MNT_PROPAGATION_MASK; + mnt_flags |= path->mnt->mnt_flags & ~MNT_USER_SETTABLE_MASK; path->mnt->mnt_flags = mnt_flags; br_write_unlock(vfsmount_lock); } diff --git a/include/linux/mount.h b/include/linux/mount.h index 604f122..dacabd6 100644 --- a/include/linux/mount.h +++ b/include/linux/mount.h @@ -42,7 +42,9 @@ struct mnt_namespace; * flag, consider how it interacts with shared mounts. */ #define MNT_SHARED_MASK (MNT_UNBINDABLE) -#define MNT_PROPAGATION_MASK (MNT_SHARED | MNT_UNBINDABLE) +#define MNT_USER_SETTABLE_MASK (MNT_NOSUID | MNT_NODEV | MNT_NOEXEC \ + | MNT_NOATIME | MNT_NODIRATIME | MNT_RELATIME \ + | MNT_READONLY) #define MNT_INTERNAL 0x4000 -- cgit v1.1