kernel/git/stable/linux.git/fs/namespace.c, branch linux-4.4.y

ovl: prevent private clone if bind mount is not allowed

2021-08-15T10:59:57+00:00

commit 427215d85e8d1476da1a86b8d67aceb485eb3631 upstream. Add the following checks from __do_loopback() to clone_private_mount() as well: - verify that the mount is in the current namespace - verify that there are no locked children Reported-by: Alois Wohlschlager Fixes: c771d683a62e ("vfs: introduce clone_private_mount()") Cc: # v3.18 Signed-off-by: Miklos Szeredi Signed-off-by: Greg Kroah-Hartman

fs/namespace.c: fix mountpoint reference counter race

2020-05-02T15:20:40+00:00

A race condition between threads updating mountpoint reference counter affects longterm releases 4.4.220, 4.9.220, 4.14.177 and 4.19.118. The mountpoint reference counter corruption may occur when: * one thread increments m_count member of struct mountpoint [under namespace_sem, but not holding mount_lock] pivot_root() * another thread simultaneously decrements the same m_count [under mount_lock, but not holding namespace_sem] put_mountpoint() unhash_mnt() umount_mnt() mntput_no_expire() To fix this race condition, grab mount_lock before updating m_count in pivot_root(). Reference: CVE-2020-12114 Cc: Al Viro Signed-off-by: Piotr Krysiuk Signed-off-by: Greg Kroah-Hartman

mount: Prevent MNT_DETACH from disconnecting locked mounts

2018-11-21T08:27:44+00:00

commit 9c8e0a1b683525464a2abe9fb4b54404a50ed2b4 upstream. Timothy Baldwin wrote: > As per mount_namespaces(7) unprivileged users should not be able to look under mount points: > > Mounts that come as a single unit from more privileged mount are locked > together and may not be separated in a less privileged mount namespace. > > However they can: > > 1. Create a mount namespace. > 2. In the mount namespace open a file descriptor to the parent of a mount point. > 3. Destroy the mount namespace. > 4. Use the file descriptor to look under the mount point. > > I have reproduced this with Linux 4.16.18 and Linux 4.18-rc8. > > The setup: > > $ sudo sysctl kernel.unprivileged_userns_clone=1 > kernel.unprivileged_userns_clone = 1 > $ mkdir -p A/B/Secret > $ sudo mount -t tmpfs hide A/B > > > "Secret" is indeed hidden as expected: > > $ ls -lR A > A: > total 0 > drwxrwxrwt 2 root root 40 Feb 12 21:08 B > > A/B: > total 0 > > > The attack revealing "Secret": > > $ unshare -Umr sh -c "exec unshare -m ls -lR /proc/self/fd/4/ 4 /proc/self/fd/4/: > total 0 > drwxr-xr-x 3 root root 60 Feb 12 21:08 B > > /proc/self/fd/4/B: > total 0 > drwxr-xr-x 2 root root 40 Feb 12 21:08 Secret > > /proc/self/fd/4/B/Secret: > total 0 I tracked this down to put_mnt_ns running passing UMOUNT_SYNC and disconnecting all of the mounts in a mount namespace. Fix this by factoring drop_mounts out of drop_collected_mounts and passing 0 instead of UMOUNT_SYNC. There are two possible behavior differences that result from this. - No longer setting UMOUNT_SYNC will no longer set MNT_SYNC_UMOUNT on the vfsmounts being unmounted. This effects the lazy rcu walk by kicking the walk out of rcu mode and forcing it to be a non-lazy walk. - No longer disconnecting locked mounts will keep some mounts around longer as they stay because the are locked to other mounts. There are only two users of drop_collected mounts: audit_tree.c and put_mnt_ns. In audit_tree.c the mounts are private and there are no rcu lazy walks only calls to iterate_mounts. So the changes should have no effect except for a small timing effect as the connected mounts are disconnected. In put_mnt_ns there may be references from process outside the mount namespace to the mounts. So the mounts remaining connected will be the bug fix that is needed. That rcu walks are allowed to continue appears not to be a problem especially as the rcu walk change was about an implementation detail not about semantics. Cc: stable@vger.kernel.org Fixes: 5ff9d8a65ce8 ("vfs: Lock in place mounts from more privileged users") Reported-by: Timothy Baldwin Tested-by: Timothy Baldwin Signed-off-by: "Eric W. Biederman" Signed-off-by: Greg Kroah-Hartman

mount: Don't allow copying MNT_UNBINDABLE|MNT_LOCKED mounts

2018-11-21T08:27:44+00:00

commit df7342b240185d58d3d9665c0bbf0a0f5570ec29 upstream. Jonathan Calmels from NVIDIA reported that he's able to bypass the mount visibility security check in place in the Linux kernel by using a combination of the unbindable property along with the private mount propagation option to allow a unprivileged user to see a path which was purposefully hidden by the root user. Reproducer: # Hide a path to all users using a tmpfs root@castiana:~# mount -t tmpfs tmpfs /sys/devices/ root@castiana:~# # As an unprivileged user, unshare user namespace and mount namespace stgraber@castiana:~$ unshare -U -m -r # Confirm the path is still not accessible root@castiana:~# ls /sys/devices/ # Make /sys recursively unbindable and private root@castiana:~# mount --make-runbindable /sys root@castiana:~# mount --make-private /sys # Recursively bind-mount the rest of /sys over to /mnnt root@castiana:~# mount --rbind /sys/ /mnt # Access our hidden /sys/device as an unprivileged user root@castiana:~# ls /mnt/devices/ breakpoint cpu cstate_core cstate_pkg i915 intel_pt isa kprobe LNXSYSTM:00 msr pci0000:00 platform pnp0 power software system tracepoint uncore_arb uncore_cbox_0 uncore_cbox_1 uprobe virtual Solve this by teaching copy_tree to fail if a mount turns out to be both unbindable and locked. Cc: stable@vger.kernel.org Fixes: 5ff9d8a65ce8 ("vfs: Lock in place mounts from more privileged users") Reported-by: Jonathan Calmels Signed-off-by: "Eric W. Biederman" Signed-off-by: Greg Kroah-Hartman

mount: Retest MNT_LOCKED in do_umount

2018-11-21T08:27:44+00:00

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

fix __legitimize_mnt()/mntput() race

2018-08-15T15:42:05+00:00

commit 119e1ef80ecfe0d1deb6378d4ab41f5b71519de1 upstream. __legitimize_mnt() has two problems - one is that in case of success the check of mount_lock is not ordered wrt preceding increment of refcount, making it possible to have successful __legitimize_mnt() on one CPU just before the otherwise final mntpu() on another, with __legitimize_mnt() not seeing mntput() taking the lock and mntput() not seeing the increment done by __legitimize_mnt(). Solved by a pair of barriers. Another is that failure of __legitimize_mnt() on the second read_seqretry() leaves us with reference that'll need to be dropped by caller; however, if that races with final mntput() we can end up with caller dropping rcu_read_lock() and doing mntput() to release that reference - with the first mntput() having freed the damn thing just as rcu_read_lock() had been dropped. Solution: in "do mntput() yourself" failure case grab mount_lock, check if MNT_DOOMED has been set by racing final mntput() that has missed our increment and if it has - undo the increment and treat that as "failure, caller doesn't need to drop anything" case. It's not easy to hit - the final mntput() has to come right after the first read_seqretry() in __legitimize_mnt() *and* manage to miss the increment done by __legitimize_mnt() before the second read_seqretry() in there. The things that are almost impossible to hit on bare hardware are not impossible on SMP KVM, though... Reported-by: Oleg Nesterov Fixes: 48a066e72d97 ("RCU'd vsfmounts") Cc: stable@vger.kernel.org Signed-off-by: Al Viro Signed-off-by: Greg Kroah-Hartman

fix mntput/mntput race

2018-08-15T15:42:05+00:00

commit 9ea0a46ca2c318fcc449c1e6b62a7230a17888f1 upstream. mntput_no_expire() does the calculation of total refcount under mount_lock; unfortunately, the decrement (as well as all increments) are done outside of it, leading to false positives in the "are we dropping the last reference" test. Consider the following situation: * mnt is a lazy-umounted mount, kept alive by two opened files. One of those files gets closed. Total refcount of mnt is 2. On CPU 42 mntput(mnt) (called from __fput()) drops one reference, decrementing component * After it has looked at component #0, the process on CPU 0 does mntget(), incrementing component #0, gets preempted and gets to run again - on CPU 69. There it does mntput(), which drops the reference (component #69) and proceeds to spin on mount_lock. * On CPU 42 our first mntput() finishes counting. It observes the decrement of component #69, but not the increment of component #0. As the result, the total it gets is not 1 as it should've been - it's 0. At which point we decide that vfsmount needs to be killed and proceed to free it and shut the filesystem down. However, there's still another opened file on that filesystem, with reference to (now freed) vfsmount, etc. and we are screwed. It's not a wide race, but it can be reproduced with artificial slowdown of the mnt_get_count() loop, and it should be easier to hit on SMP KVM setups. Fix consists of moving the refcount decrement under mount_lock; the tricky part is that we want (and can) keep the fast case (i.e. mount that still has non-NULL ->mnt_ns) entirely out of mount_lock. All places that zero mnt->mnt_ns are dropping some reference to mnt and they call synchronize_rcu() before that mntput(). IOW, if mntput() observes (under rcu_read_lock()) a non-NULL ->mnt_ns, it is guaranteed that there is another reference yet to be dropped. Reported-by: Jann Horn Tested-by: Jann Horn Fixes: 48a066e72d97 ("RCU'd vsfmounts") Cc: stable@vger.kernel.org Signed-off-by: Al Viro Signed-off-by: Greg Kroah-Hartman

Don't leak MNT_INTERNAL away from internal mounts

2018-04-24T07:32:11+00:00

commit 16a34adb9392b2fe4195267475ab5b472e55292c upstream. We want it only for the stuff created by SB_KERNMOUNT mounts, *not* for their copies. As it is, creating a deep stack of bindings of /proc/*/ns/* somewhere in a new namespace and exiting yields a stack overflow. Cc: stable@kernel.org Reported-by: Alexander Aring Bisected-by: Kirill Tkhai Tested-by: Kirill Tkhai Tested-by: Alexander Aring Signed-off-by: Al Viro Signed-off-by: Greg Kroah-Hartman

mnt: In propgate_umount handle visiting mounts in any order

2017-07-21T05:44:57+00:00

commit 99b19d16471e9c3faa85cad38abc9cbbe04c6d55 upstream. While investigating some poor umount performance I realized that in the case of overlapping mount trees where some of the mounts are locked the code has been failing to unmount all of the mounts it should have been unmounting. This failure to unmount all of the necessary mounts can be reproduced with: $ cat locked_mounts_test.sh mount -t tmpfs test-base /mnt mount --make-shared /mnt mkdir -p /mnt/b mount -t tmpfs test1 /mnt/b mount --make-shared /mnt/b mkdir -p /mnt/b/10 mount -t tmpfs test2 /mnt/b/10 mount --make-shared /mnt/b/10 mkdir -p /mnt/b/10/20 mount --rbind /mnt/b /mnt/b/10/20 unshare -Urm --propagation unchaged /bin/sh -c 'sleep 5; if [ $(grep test /proc/self/mountinfo | wc -l) -eq 1 ] ; then echo SUCCESS ; else echo FAILURE ; fi' sleep 1 umount -l /mnt/b wait %% $ unshare -Urm ./locked_mounts_test.sh This failure is corrected by removing the prepass that marks mounts that may be umounted. A first pass is added that umounts mounts if possible and if not sets mount mark if they could be unmounted if they weren't locked and adds them to a list to umount possibilities. This first pass reconsiders the mounts parent if it is on the list of umount possibilities, ensuring that information of umoutability will pass from child to mount parent. A second pass then walks through all mounts that are umounted and processes their children unmounting them or marking them for reparenting. A last pass cleans up the state on the mounts that could not be umounted and if applicable reparents them to their first parent that remained mounted. While a bit longer than the old code this code is much more robust as it allows information to flow up from the leaves and down from the trunk making the order in which mounts are encountered in the umount propgation tree irrelevant. Fixes: 0c56fe31420c ("mnt: Don't propagate unmounts to locked mounts") Reviewed-by: Andrei Vagin Signed-off-by: "Eric W. Biederman" Signed-off-by: Greg Kroah-Hartman

mnt: In umount propagation reparent in a separate pass

2017-07-21T05:44:57+00:00

commit 570487d3faf2a1d8a220e6ee10f472163123d7da upstream. It was observed that in some pathlogical cases that the current code does not unmount everything it should. After investigation it was determined that the issue is that mnt_change_mntpoint can can change which mounts are available to be unmounted during mount propagation which is wrong. The trivial reproducer is: $ cat ./pathological.sh mount -t tmpfs test-base /mnt cd /mnt mkdir 1 2 1/1 mount --bind 1 1 mount --make-shared 1 mount --bind 1 2 mount --bind 1/1 1/1 mount --bind 1/1 1/1 echo grep test-base /proc/self/mountinfo umount 1/1 echo grep test-base /proc/self/mountinfo $ unshare -Urm ./pathological.sh The expected output looks like: 46 31 0:25 / /mnt rw,relatime - tmpfs test-base rw,uid=1000,gid=1000 47 46 0:25 /1 /mnt/1 rw,relatime shared:1 - tmpfs test-base rw,uid=1000,gid=1000 48 46 0:25 /1 /mnt/2 rw,relatime shared:1 - tmpfs test-base rw,uid=1000,gid=1000 49 54 0:25 /1/1 /mnt/1/1 rw,relatime shared:1 - tmpfs test-base rw,uid=1000,gid=1000 50 53 0:25 /1/1 /mnt/2/1 rw,relatime shared:1 - tmpfs test-base rw,uid=1000,gid=1000 51 49 0:25 /1/1 /mnt/1/1 rw,relatime shared:1 - tmpfs test-base rw,uid=1000,gid=1000 54 47 0:25 /1/1 /mnt/1/1 rw,relatime shared:1 - tmpfs test-base rw,uid=1000,gid=1000 53 48 0:25 /1/1 /mnt/2/1 rw,relatime shared:1 - tmpfs test-base rw,uid=1000,gid=1000 52 50 0:25 /1/1 /mnt/2/1 rw,relatime shared:1 - tmpfs test-base rw,uid=1000,gid=1000 46 31 0:25 / /mnt rw,relatime - tmpfs test-base rw,uid=1000,gid=1000 47 46 0:25 /1 /mnt/1 rw,relatime shared:1 - tmpfs test-base rw,uid=1000,gid=1000 48 46 0:25 /1 /mnt/2 rw,relatime shared:1 - tmpfs test-base rw,uid=1000,gid=1000 The output without the fix looks like: 46 31 0:25 / /mnt rw,relatime - tmpfs test-base rw,uid=1000,gid=1000 47 46 0:25 /1 /mnt/1 rw,relatime shared:1 - tmpfs test-base rw,uid=1000,gid=1000 48 46 0:25 /1 /mnt/2 rw,relatime shared:1 - tmpfs test-base rw,uid=1000,gid=1000 49 54 0:25 /1/1 /mnt/1/1 rw,relatime shared:1 - tmpfs test-base rw,uid=1000,gid=1000 50 53 0:25 /1/1 /mnt/2/1 rw,relatime shared:1 - tmpfs test-base rw,uid=1000,gid=1000 51 49 0:25 /1/1 /mnt/1/1 rw,relatime shared:1 - tmpfs test-base rw,uid=1000,gid=1000 54 47 0:25 /1/1 /mnt/1/1 rw,relatime shared:1 - tmpfs test-base rw,uid=1000,gid=1000 53 48 0:25 /1/1 /mnt/2/1 rw,relatime shared:1 - tmpfs test-base rw,uid=1000,gid=1000 52 50 0:25 /1/1 /mnt/2/1 rw,relatime shared:1 - tmpfs test-base rw,uid=1000,gid=1000 46 31 0:25 / /mnt rw,relatime - tmpfs test-base rw,uid=1000,gid=1000 47 46 0:25 /1 /mnt/1 rw,relatime shared:1 - tmpfs test-base rw,uid=1000,gid=1000 48 46 0:25 /1 /mnt/2 rw,relatime shared:1 - tmpfs test-base rw,uid=1000,gid=1000 52 48 0:25 /1/1 /mnt/2/1 rw,relatime shared:1 - tmpfs test-base rw,uid=1000,gid=1000 That last mount in the output was in the propgation tree to be unmounted but was missed because the mnt_change_mountpoint changed it's parent before the walk through the mount propagation tree observed it. Fixes: 1064f874abc0 ("mnt: Tuck mounts under others instead of creating shadow/side mounts.") Acked-by: Andrei Vagin Reviewed-by: Ram Pai Signed-off-by: "Eric W. Biederman" Signed-off-by: Greg Kroah-Hartman