This is a note to let you know that I've just added the patch titled
mnt: Only change user settable mount flags in remount
to the 3.16-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
mnt-only-change-user-settable-mount-flags-in-remount.patch
and it can be found in the queue-3.16 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From a6138db815df5ee542d848318e5dae681590fccd Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
Date: Mon, 28 Jul 2014 16:26:53 -0700
Subject: mnt: Only change user settable mount flags in remount
From: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
commit a6138db815df5ee542d848318e5dae681590fccd upstream.
Kenton Varda <kenton@xxxxxxxxxxxx> 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.
Acked-by: Serge E. Hallyn <serge.hallyn@xxxxxxxxxx>
Signed-off-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
fs/namespace.c | 2 +-
include/linux/mount.h | 4 +++-
2 files changed, 4 insertions(+), 2 deletions(-)
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1937,7 +1937,7 @@ static int do_remount(struct path *path,
err = do_remount_sb(sb, flags, data, 0);
if (!err) {
lock_mount_hash();
- mnt_flags |= mnt->mnt.mnt_flags & MNT_PROPAGATION_MASK;
+ mnt_flags |= mnt->mnt.mnt_flags & ~MNT_USER_SETTABLE_MASK;
mnt->mnt.mnt_flags = mnt_flags;
touch_mnt_namespace(mnt->mnt_ns);
unlock_mount_hash();
--- 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_FLAGS (MNT_SHARED | MNT_WRITE_HOLD | MNT_INTERNAL | \
MNT_DOOMED | MNT_SYNC_UMOUNT | MNT_MARKED)
Patches currently in stable-queue which might be from ebiederm@xxxxxxxxxxxx are
queue-3.16/mnt-correct-permission-checks-in-do_remount.patch
queue-3.16/mnt-only-change-user-settable-mount-flags-in-remount.patch
queue-3.16/mnt-add-tests-for-unprivileged-remount-cases-that-have-found-to-be-faulty.patch
queue-3.16/mnt-change-the-default-remount-atime-from-relatime-to-the-existing-value.patch
queue-3.16/mnt-move-the-test-for-mnt_lock_readonly-from-change_mount_flags-into-do_remount.patch
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