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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>
57 lines
1.9 KiB
C
57 lines
1.9 KiB
C
/*
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* linux/fs/pnode.h
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*
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* (C) Copyright IBM Corporation 2005.
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* Released under GPL v2.
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*
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*/
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#ifndef _LINUX_PNODE_H
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#define _LINUX_PNODE_H
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#include <linux/list.h>
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#include "mount.h"
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#define IS_MNT_SHARED(m) ((m)->mnt.mnt_flags & MNT_SHARED)
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#define IS_MNT_SLAVE(m) ((m)->mnt_master)
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#define IS_MNT_NEW(m) (!(m)->mnt_ns)
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#define CLEAR_MNT_SHARED(m) ((m)->mnt.mnt_flags &= ~MNT_SHARED)
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#define IS_MNT_UNBINDABLE(m) ((m)->mnt.mnt_flags & MNT_UNBINDABLE)
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#define IS_MNT_MARKED(m) ((m)->mnt.mnt_flags & MNT_MARKED)
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#define SET_MNT_MARK(m) ((m)->mnt.mnt_flags |= MNT_MARKED)
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#define CLEAR_MNT_MARK(m) ((m)->mnt.mnt_flags &= ~MNT_MARKED)
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#define IS_MNT_LOCKED(m) ((m)->mnt.mnt_flags & MNT_LOCKED)
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#define CL_EXPIRE 0x01
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#define CL_SLAVE 0x02
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#define CL_COPY_UNBINDABLE 0x04
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#define CL_MAKE_SHARED 0x08
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#define CL_PRIVATE 0x10
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#define CL_SHARED_TO_SLAVE 0x20
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#define CL_UNPRIVILEGED 0x40
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#define CL_COPY_MNT_NS_FILE 0x80
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#define CL_COPY_ALL (CL_COPY_UNBINDABLE | CL_COPY_MNT_NS_FILE)
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static inline void set_mnt_shared(struct mount *mnt)
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{
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mnt->mnt.mnt_flags &= ~MNT_SHARED_MASK;
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mnt->mnt.mnt_flags |= MNT_SHARED;
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}
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void change_mnt_propagation(struct mount *, int);
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int propagate_mnt(struct mount *, struct mountpoint *, struct mount *,
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struct hlist_head *);
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int propagate_umount(struct list_head *);
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int propagate_mount_busy(struct mount *, int);
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void propagate_mount_unlock(struct mount *);
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void mnt_release_group_id(struct mount *);
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int get_dominating_id(struct mount *mnt, const struct path *root);
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unsigned int mnt_get_count(struct mount *mnt);
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void mnt_set_mountpoint(struct mount *, struct mountpoint *,
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struct mount *);
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struct mount *copy_tree(struct mount *, struct dentry *, int);
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bool is_path_reachable(struct mount *, struct dentry *,
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const struct path *root);
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int count_mounts(struct mnt_namespace *ns, struct mount *mnt);
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#endif /* _LINUX_PNODE_H */
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