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mount: Retest MNT_LOCKED in do_umount

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commit 25d202ed820ee347edec0bf3bf553544556bf64b upstream.

It was recently pointed out that the one instance of testing MNT_LOCKED
outside of the namespace_sem is in ksys_umount.

Fix that by adding a test inside of do_umount with namespace_sem and
the mount_lock held.  As it helps to fail fails the existing test is
maintained with an additional comment pointing out that it may be racy
because the locks are not held.

Cc: stable@vger.kernel.org
Reported-by: Al Viro <viro@ZenIV.linux.org.uk>
Fixes: 5ff9d8a65ce8 ("vfs: Lock in place mounts from more privileged users")
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Eric W. Biederman 2018-10-22 10:21:38 -05:00 committed by Greg Kroah-Hartman
parent 68b908750e
commit 5e64ee8788
1 changed files with 8 additions and 2 deletions
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10
fs/namespace.c
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@ -1625,8 +1625,13 @@ static int do_umount(struct mount *mnt, int flags)
namespace_lock();
lock_mount_hash();
event++;
/* Recheck MNT_LOCKED with the locks held */
retval = -EINVAL;
if (mnt->mnt.mnt_flags & MNT_LOCKED)
goto out;
event++;
if (flags & MNT_DETACH) {
if (!list_empty(&mnt->mnt_list))
umount_tree(mnt, UMOUNT_PROPAGATE);
@ -1640,6 +1645,7 @@ static int do_umount(struct mount *mnt, int flags)
retval = 0;
}
}
out:
unlock_mount_hash();
namespace_unlock();
return retval;
@ -1730,7 +1736,7 @@ SYSCALL_DEFINE2(umount, char __user *, name, int, flags)
goto dput_and_out;
if (!check_mnt(mnt))
goto dput_and_out;
if (mnt->mnt.mnt_flags & MNT_LOCKED)
if (mnt->mnt.mnt_flags & MNT_LOCKED) /* Check optimistically */
goto dput_and_out;
retval = -EPERM;
if (flags & MNT_FORCE && !capable(CAP_SYS_ADMIN))