From fa14e9bddc7d0ca7a2b0073286ed86f343ae771d Mon Sep 17 00:00:00 2001 From: "Eric W. Biederman" Date: Mon, 22 Oct 2018 10:21:38 -0500 Subject: [PATCH] mount: Retest MNT_LOCKED in do_umount 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 Fixes: 5ff9d8a65ce8 ("vfs: Lock in place mounts from more privileged users") Signed-off-by: "Eric W. Biederman" Signed-off-by: Greg Kroah-Hartman --- fs/namespace.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/fs/namespace.c b/fs/namespace.c index 0a9e766b4087..7ca287c9080a 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -1599,8 +1599,13 @@ 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); @@ -1614,6 +1619,7 @@ static int do_umount(struct mount *mnt, int flags) retval = 0; } } +out: unlock_mount_hash(); namespace_unlock(); return retval; @@ -1704,7 +1710,7 @@ 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)) -- 2.20.1