user/sven/linux.git/fs/pnode.c, branch v4.9.5

mnt: Add a per mount namespace limit on the number of mounts

2016-09-30T17:46:48Z

CAI Qian pointed out that the semantics of shared subtrees make it possible to create an exponentially increasing number of mounts in a mount namespace. mkdir /tmp/1 /tmp/2 mount --make-rshared / for i in $(seq 1 20) ; do mount --bind /tmp/1 /tmp/2 ; done Will create create 2^20 or 1048576 mounts, which is a practical problem as some people have managed to hit this by accident. As such CVE-2016-6213 was assigned. Ian Kent described the situation for autofs users as follows: > The number of mounts for direct mount maps is usually not very large because of > the way they are implemented, large direct mount maps can have performance > problems. There can be anywhere from a few (likely case a few hundred) to less > than 10000, plus mounts that have been triggered and not yet expired. > > Indirect mounts have one autofs mount at the root plus the number of mounts that > have been triggered and not yet expired. > > The number of autofs indirect map entries can range from a few to the common > case of several thousand and in rare cases up to between 30000 and 50000. I've > not heard of people with maps larger than 50000 entries. > > The larger the number of map entries the greater the possibility for a large > number of active mounts so it's not hard to expect cases of a 1000 or somewhat > more active mounts. So I am setting the default number of mounts allowed per mount namespace at 100,000. This is more than enough for any use case I know of, but small enough to quickly stop an exponential increase in mounts. Which should be perfect to catch misconfigurations and malfunctioning programs. For anyone who needs a higher limit this can be changed by writing to the new /proc/sys/fs/mount-max sysctl. Tested-by: CAI Qian Signed-off-by: "Eric W. Biederman"

propogate_mnt: Handle the first propogated copy being a slave

2016-05-05T14:54:45Z

When the first propgated copy was a slave the following oops would result: > BUG: unable to handle kernel NULL pointer dereference at 0000000000000010 > IP: [] propagate_one+0xbe/0x1c0 > PGD bacd4067 PUD bac66067 PMD 0 > Oops: 0000 [#1] SMP > Modules linked in: > CPU: 1 PID: 824 Comm: mount Not tainted 4.6.0-rc5userns+ #1523 > Hardware name: Bochs Bochs, BIOS Bochs 01/01/2007 > task: ffff8800bb0a8000 ti: ffff8800bac3c000 task.ti: ffff8800bac3c000 > RIP: 0010:[] [] propagate_one+0xbe/0x1c0 > RSP: 0018:ffff8800bac3fd38 EFLAGS: 00010283 > RAX: 0000000000000000 RBX: ffff8800bb77ec00 RCX: 0000000000000010 > RDX: 0000000000000000 RSI: ffff8800bb58c000 RDI: ffff8800bb58c480 > RBP: ffff8800bac3fd48 R08: 0000000000000001 R09: 0000000000000000 > R10: 0000000000001ca1 R11: 0000000000001c9d R12: 0000000000000000 > R13: ffff8800ba713800 R14: ffff8800bac3fda0 R15: ffff8800bb77ec00 > FS: 00007f3c0cd9b7e0(0000) GS:ffff8800bfb00000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 0000000000000010 CR3: 00000000bb79d000 CR4: 00000000000006e0 > Stack: > ffff8800bb77ec00 0000000000000000 ffff8800bac3fd88 ffffffff811fbf85 > ffff8800bac3fd98 ffff8800bb77f080 ffff8800ba713800 ffff8800bb262b40 > 0000000000000000 0000000000000000 ffff8800bac3fdd8 ffffffff811f1da0 > Call Trace: > [] propagate_mnt+0x105/0x140 > [] attach_recursive_mnt+0x120/0x1e0 > [] graft_tree+0x63/0x70 > [] do_add_mount+0x9b/0x100 > [] do_mount+0x2aa/0xdf0 > [] ? strndup_user+0x4e/0x70 > [] SyS_mount+0x75/0xc0 > [] do_syscall_64+0x4b/0xa0 > [] entry_SYSCALL64_slow_path+0x25/0x25 > Code: 00 00 75 ec 48 89 0d 02 22 22 01 8b 89 10 01 00 00 48 89 05 fd 21 22 01 39 8e 10 01 00 00 0f 84 e0 00 00 00 48 8b 80 d8 00 00 00 <48> 8b 50 10 48 89 05 df 21 22 01 48 89 15 d0 21 22 01 8b 53 30 > RIP [] propagate_one+0xbe/0x1c0 > RSP > CR2: 0000000000000010 > ---[ end trace 2725ecd95164f217 ]--- This oops happens with the namespace_sem held and can be triggered by non-root users. An all around not pleasant experience. To avoid this scenario when finding the appropriate source mount to copy stop the walk up the mnt_master chain when the first source mount is encountered. Further rewrite the walk up the last_source mnt_master chain so that it is clear what is going on. The reason why the first source mount is special is that it it's mnt_parent is not a mount in the dest_mnt propagation tree, and as such termination conditions based up on the dest_mnt mount propgation tree do not make sense. To avoid other kinds of confusion last_dest is not changed when computing last_source. last_dest is only used once in propagate_one and that is above the point of the code being modified, so changing the global variable is meaningless and confusing. Cc: stable@vger.kernel.org fixes: f2ebb3a921c1ca1e2ddd9242e95a1989a50c4c68 ("smarter propagate_mnt()") Reported-by: Tycho Andersen Reviewed-by: Seth Forshee Tested-by: Seth Forshee Signed-off-by: "Eric W. Biederman"

fs/pnode.c: treat zero mnt_group_id-s as unequal

2016-02-20T05:15:52Z

propagate_one(m) calculates "type" argument for copy_tree() like this: > if (m->mnt_group_id == last_dest->mnt_group_id) { > type = CL_MAKE_SHARED; > } else { > type = CL_SLAVE; > if (IS_MNT_SHARED(m)) > type |= CL_MAKE_SHARED; > } The "type" argument then governs clone_mnt() behavior with respect to flags and mnt_master of new mount. When we iterate through a slave group, it is possible that both current "m" and "last_dest" are not shared (although, both are slaves, i.e. have non-NULL mnt_master-s). Then the comparison above erroneously makes new mount shared and sets its mnt_master to last_source->mnt_master. The patch fixes the problem by handling zero mnt_group_id-s as though they are unequal. The similar problem exists in the implementation of "else" clause above when we have to ascend upward in the master/slave tree by calling: > last_source = last_source->mnt_master; > last_dest = last_source->mnt_parent; proper number of times. The last step is governed by "n->mnt_group_id != last_dest->mnt_group_id" condition that may lie if both are zero. The patch fixes this case in the same way as the former one. [AV: don't open-code an obvious helper...] Signed-off-by: Maxim Patlasov Signed-off-by: Al Viro

mnt: Don't propagate unmounts to locked mounts

2015-04-03T01:34:20Z

If the first mount in shared subtree is locked don't unmount the shared subtree. This is ensured by walking through the mounts parents before children and marking a mount as unmountable if it is not locked or it is locked but it's parent is marked. This allows recursive mount detach to propagate through a set of mounts when unmounting them would not reveal what is under any locked mount. Cc: stable@vger.kernel.org Signed-off-by: "Eric W. Biederman"

mnt: On an unmount propagate clearing of MNT_LOCKED

2015-04-03T01:34:19Z

A prerequisite of calling umount_tree is that the point where the tree is mounted at is valid to unmount. If we are propagating the effect of the unmount clear MNT_LOCKED in every instance where the same filesystem is mounted on the same mountpoint in the mount tree, as we know (by virtue of the fact that umount_tree was called) that it is safe to reveal what is at that mountpoint. Cc: stable@vger.kernel.org Signed-off-by: "Eric W. Biederman"

mnt: Delay removal from the mount hash.

2015-04-03T01:34:19Z

- Modify __lookup_mnt_hash_last to ignore mounts that have MNT_UMOUNTED set. - Don't remove mounts from the mount hash table in propogate_umount - Don't remove mounts from the mount hash table in umount_tree before the entire list of mounts to be umounted is selected. - Remove mounts from the mount hash table as the last thing that happens in the case where a mount has a parent in umount_tree. Mounts without parents are not hashed (by definition). This paves the way for delaying removal from the mount hash table even farther and fixing the MNT_LOCKED vs MNT_DETACH issue. Cc: stable@vger.kernel.org Signed-off-by: "Eric W. Biederman"

mnt: Add MNT_UMOUNT flag

2015-04-03T01:34:18Z

In some instances it is necessary to know if the the unmounting process has begun on a mount. Add MNT_UMOUNT to make that reliably testable. This fix gets used in fixing locked mounts in MNT_DETACH Cc: stable@vger.kernel.org Signed-off-by: "Eric W. Biederman"

mnt: In umount_tree reuse mnt_list instead of mnt_hash

2015-04-03T01:34:18Z

umount_tree builds a list of mounts that need to be unmounted. Utilize mnt_list for this purpose instead of mnt_hash. This begins to allow keeping a mount on the mnt_hash after it is unmounted, which is necessary for a properly functioning MNT_LOCKED implementation. The fact that mnt_list is an ordinary list makding available list_move is nice bonus. Cc: stable@vger.kernel.org Signed-off-by: "Eric W. Biederman"

mnt: Move the clear of MNT_LOCKED from copy_tree to it's callers.

2014-12-02T16:46:50Z

Clear MNT_LOCKED in the callers of copy_tree except copy_mnt_ns, and collect_mounts. In copy_mnt_ns it is necessary to create an exact copy of a mount tree, so not clearing MNT_LOCKED is important. Similarly collect_mounts is used to take a snapshot of the mount tree for audit logging purposes and auditing using a faithful copy of the tree is important. This becomes particularly significant when we start setting MNT_LOCKED on rootfs to prevent it from being unmounted. Signed-off-by: "Eric W. Biederman"

get rid of propagate_umount() mistakenly treating slaves as busy.

2014-08-30T22:31:41Z

The check in __propagate_umount() ("has somebody explicitly mounted something on that slave?") is done *before* taking the already doomed victims out of the child lists. Cc: stable@vger.kernel.org Signed-off-by: Al Viro