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author | Eric W. Biederman <ebiederm@xmission.com> | 2016-09-28 07:27:17 +0200 |
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committer | Eric W. Biederman <ebiederm@xmission.com> | 2016-09-30 19:46:48 +0200 |
commit | d29216842a85c7970c536108e093963f02714498 (patch) | |
tree | acf8843f0c807e80fc3b15653f3b22136984c69a /fs/mount.h | |
parent | netns: move {inc,dec}_net_namespaces into #ifdef (diff) | |
download | linux-d29216842a85c7970c536108e093963f02714498.tar.xz linux-d29216842a85c7970c536108e093963f02714498.zip |
mnt: Add a per mount namespace limit on the number of mounts
CAI Qian <caiqian@redhat.com> 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 <raven@themaw.net> 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 <caiqian@redhat.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Diffstat (limited to 'fs/mount.h')
-rw-r--r-- | fs/mount.h | 2 |
1 files changed, 2 insertions, 0 deletions
diff --git a/fs/mount.h b/fs/mount.h index e037981d8351..d2e25d7b64b3 100644 --- a/fs/mount.h +++ b/fs/mount.h @@ -14,6 +14,8 @@ struct mnt_namespace { u64 seq; /* Sequence number to prevent loops */ wait_queue_head_t poll; u64 event; + unsigned int mounts; /* # of mounts in the namespace */ + unsigned int pending_mounts; }; struct mnt_pcp { |