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d29216842a
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>
141 lines
3.6 KiB
C
141 lines
3.6 KiB
C
#include <linux/mount.h>
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#include <linux/seq_file.h>
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#include <linux/poll.h>
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#include <linux/ns_common.h>
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#include <linux/fs_pin.h>
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struct mnt_namespace {
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atomic_t count;
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struct ns_common ns;
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struct mount * root;
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struct list_head list;
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struct user_namespace *user_ns;
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struct ucounts *ucounts;
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u64 seq; /* Sequence number to prevent loops */
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wait_queue_head_t poll;
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u64 event;
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unsigned int mounts; /* # of mounts in the namespace */
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unsigned int pending_mounts;
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};
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struct mnt_pcp {
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int mnt_count;
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int mnt_writers;
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};
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struct mountpoint {
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struct hlist_node m_hash;
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struct dentry *m_dentry;
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struct hlist_head m_list;
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int m_count;
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};
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struct mount {
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struct hlist_node mnt_hash;
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struct mount *mnt_parent;
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struct dentry *mnt_mountpoint;
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struct vfsmount mnt;
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union {
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struct rcu_head mnt_rcu;
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struct llist_node mnt_llist;
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};
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#ifdef CONFIG_SMP
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struct mnt_pcp __percpu *mnt_pcp;
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#else
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int mnt_count;
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int mnt_writers;
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#endif
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struct list_head mnt_mounts; /* list of children, anchored here */
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struct list_head mnt_child; /* and going through their mnt_child */
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struct list_head mnt_instance; /* mount instance on sb->s_mounts */
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const char *mnt_devname; /* Name of device e.g. /dev/dsk/hda1 */
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struct list_head mnt_list;
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struct list_head mnt_expire; /* link in fs-specific expiry list */
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struct list_head mnt_share; /* circular list of shared mounts */
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struct list_head mnt_slave_list;/* list of slave mounts */
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struct list_head mnt_slave; /* slave list entry */
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struct mount *mnt_master; /* slave is on master->mnt_slave_list */
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struct mnt_namespace *mnt_ns; /* containing namespace */
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struct mountpoint *mnt_mp; /* where is it mounted */
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struct hlist_node mnt_mp_list; /* list mounts with the same mountpoint */
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#ifdef CONFIG_FSNOTIFY
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struct hlist_head mnt_fsnotify_marks;
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__u32 mnt_fsnotify_mask;
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#endif
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int mnt_id; /* mount identifier */
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int mnt_group_id; /* peer group identifier */
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int mnt_expiry_mark; /* true if marked for expiry */
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struct hlist_head mnt_pins;
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struct fs_pin mnt_umount;
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struct dentry *mnt_ex_mountpoint;
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};
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#define MNT_NS_INTERNAL ERR_PTR(-EINVAL) /* distinct from any mnt_namespace */
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static inline struct mount *real_mount(struct vfsmount *mnt)
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{
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return container_of(mnt, struct mount, mnt);
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}
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static inline int mnt_has_parent(struct mount *mnt)
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{
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return mnt != mnt->mnt_parent;
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}
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static inline int is_mounted(struct vfsmount *mnt)
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{
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/* neither detached nor internal? */
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return !IS_ERR_OR_NULL(real_mount(mnt)->mnt_ns);
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}
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extern struct mount *__lookup_mnt(struct vfsmount *, struct dentry *);
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extern struct mount *__lookup_mnt_last(struct vfsmount *, struct dentry *);
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extern int __legitimize_mnt(struct vfsmount *, unsigned);
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extern bool legitimize_mnt(struct vfsmount *, unsigned);
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extern void __detach_mounts(struct dentry *dentry);
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static inline void detach_mounts(struct dentry *dentry)
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{
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if (!d_mountpoint(dentry))
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return;
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__detach_mounts(dentry);
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}
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static inline void get_mnt_ns(struct mnt_namespace *ns)
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{
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atomic_inc(&ns->count);
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}
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extern seqlock_t mount_lock;
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static inline void lock_mount_hash(void)
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{
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write_seqlock(&mount_lock);
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}
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static inline void unlock_mount_hash(void)
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{
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write_sequnlock(&mount_lock);
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}
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struct proc_mounts {
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struct mnt_namespace *ns;
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struct path root;
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int (*show)(struct seq_file *, struct vfsmount *);
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void *cached_mount;
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u64 cached_event;
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loff_t cached_index;
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};
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extern const struct seq_operations mounts_op;
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extern bool __is_local_mountpoint(struct dentry *dentry);
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static inline bool is_local_mountpoint(struct dentry *dentry)
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{
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if (!d_mountpoint(dentry))
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return false;
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return __is_local_mountpoint(dentry);
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}
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