mnt: Add a per mount namespace limit on the number of mounts (CVE-2016-6213)
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@ -236,6 +236,8 @@ linux (4.8.11-1) UNRELEASED; urgency=medium
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* mpi: Fix NULL ptr dereference in mpi_powm() (CVE-2016-8650)
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* vfio/pci: Fix integer overflows, bitmask check (CVE-2016-9083
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CVE-2016-9084)
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* mnt: Add a per mount namespace limit on the number of mounts
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(CVE-2016-6213)
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[ Ben Hutchings ]
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* [arm64] Enable more drivers for X-Gene (Really closes: #840061):
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266
debian/patches/bugfix/all/mnt-Add-a-per-mount-namespace-limit-on-the-number-of.patch
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266
debian/patches/bugfix/all/mnt-Add-a-per-mount-namespace-limit-on-the-number-of.patch
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@ -0,0 +1,266 @@
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From: "Eric W. Biederman" <ebiederm@xmission.com>
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Date: Wed, 28 Sep 2016 00:27:17 -0500
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Subject: mnt: Add a per mount namespace limit on the number of mounts
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Origin: https://git.kernel.org/linus/d29216842a85c7970c536108e093963f02714498
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CAI Qian <caiqian@redhat.com> pointed out that the semantics
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of shared subtrees make it possible to create an exponentially
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increasing number of mounts in a mount namespace.
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mkdir /tmp/1 /tmp/2
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mount --make-rshared /
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for i in $(seq 1 20) ; do mount --bind /tmp/1 /tmp/2 ; done
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Will create create 2^20 or 1048576 mounts, which is a practical problem
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as some people have managed to hit this by accident.
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As such CVE-2016-6213 was assigned.
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Ian Kent <raven@themaw.net> described the situation for autofs users
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as follows:
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> The number of mounts for direct mount maps is usually not very large because of
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> the way they are implemented, large direct mount maps can have performance
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> problems. There can be anywhere from a few (likely case a few hundred) to less
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> than 10000, plus mounts that have been triggered and not yet expired.
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>
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> Indirect mounts have one autofs mount at the root plus the number of mounts that
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> have been triggered and not yet expired.
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>
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> The number of autofs indirect map entries can range from a few to the common
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> case of several thousand and in rare cases up to between 30000 and 50000. I've
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> not heard of people with maps larger than 50000 entries.
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>
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> The larger the number of map entries the greater the possibility for a large
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> number of active mounts so it's not hard to expect cases of a 1000 or somewhat
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> more active mounts.
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So I am setting the default number of mounts allowed per mount
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namespace at 100,000. This is more than enough for any use case I
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know of, but small enough to quickly stop an exponential increase
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in mounts. Which should be perfect to catch misconfigurations and
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malfunctioning programs.
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For anyone who needs a higher limit this can be changed by writing
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to the new /proc/sys/fs/mount-max sysctl.
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Tested-by: CAI Qian <caiqian@redhat.com>
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Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
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[carnil: Adjust context for 4.8]
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---
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Documentation/sysctl/fs.txt | 7 +++++++
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fs/mount.h | 2 ++
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fs/namespace.c | 49 ++++++++++++++++++++++++++++++++++++++++++++-
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fs/pnode.c | 2 +-
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fs/pnode.h | 1 +
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include/linux/mount.h | 2 ++
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kernel/sysctl.c | 9 +++++++++
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7 files changed, 70 insertions(+), 2 deletions(-)
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--- a/Documentation/sysctl/fs.txt
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+++ b/Documentation/sysctl/fs.txt
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@@ -265,6 +265,13 @@ aio-nr can grow to.
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==============================================================
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+mount-max:
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+
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+This denotes the maximum number of mounts that may exist
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+in a mount namespace.
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+
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+==============================================================
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+
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2. /proc/sys/fs/binfmt_misc
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----------------------------------------------------------
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--- a/fs/mount.h
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+++ b/fs/mount.h
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@@ -13,6 +13,8 @@ struct mnt_namespace {
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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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--- a/fs/namespace.c
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+++ b/fs/namespace.c
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@@ -27,6 +27,9 @@
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#include "pnode.h"
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#include "internal.h"
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+/* Maximum number of mounts in a mount namespace */
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+unsigned int sysctl_mount_max __read_mostly = 100000;
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+
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static unsigned int m_hash_mask __read_mostly;
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static unsigned int m_hash_shift __read_mostly;
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static unsigned int mp_hash_mask __read_mostly;
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@@ -900,6 +903,9 @@ static void commit_tree(struct mount *mn
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list_splice(&head, n->list.prev);
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+ n->mounts += n->pending_mounts;
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+ n->pending_mounts = 0;
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+
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attach_shadowed(mnt, parent, shadows);
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touch_mnt_namespace(n);
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}
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@@ -1420,11 +1426,16 @@ static void umount_tree(struct mount *mn
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propagate_umount(&tmp_list);
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while (!list_empty(&tmp_list)) {
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+ struct mnt_namespace *ns;
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bool disconnect;
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p = list_first_entry(&tmp_list, struct mount, mnt_list);
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list_del_init(&p->mnt_expire);
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list_del_init(&p->mnt_list);
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- __touch_mnt_namespace(p->mnt_ns);
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+ ns = p->mnt_ns;
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+ if (ns) {
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+ ns->mounts--;
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+ __touch_mnt_namespace(ns);
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+ }
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p->mnt_ns = NULL;
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if (how & UMOUNT_SYNC)
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p->mnt.mnt_flags |= MNT_SYNC_UMOUNT;
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@@ -1842,6 +1853,28 @@ static int invent_group_ids(struct mount
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return 0;
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}
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+int count_mounts(struct mnt_namespace *ns, struct mount *mnt)
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+{
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+ unsigned int max = READ_ONCE(sysctl_mount_max);
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+ unsigned int mounts = 0, old, pending, sum;
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+ struct mount *p;
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+
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+ for (p = mnt; p; p = next_mnt(p, mnt))
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+ mounts++;
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+
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+ old = ns->mounts;
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+ pending = ns->pending_mounts;
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+ sum = old + pending;
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+ if ((old > sum) ||
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+ (pending > sum) ||
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+ (max < sum) ||
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+ (mounts > (max - sum)))
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+ return -ENOSPC;
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+
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+ ns->pending_mounts = pending + mounts;
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+ return 0;
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+}
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+
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/*
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* @source_mnt : mount tree to be attached
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* @nd : place the mount tree @source_mnt is attached
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@@ -1911,10 +1944,18 @@ static int attach_recursive_mnt(struct m
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struct path *parent_path)
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{
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HLIST_HEAD(tree_list);
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+ struct mnt_namespace *ns = dest_mnt->mnt_ns;
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struct mount *child, *p;
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struct hlist_node *n;
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int err;
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+ /* Is there space to add these mounts to the mount namespace? */
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+ if (!parent_path) {
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+ err = count_mounts(ns, source_mnt);
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+ if (err)
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+ goto out;
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+ }
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+
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if (IS_MNT_SHARED(dest_mnt)) {
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err = invent_group_ids(source_mnt, true);
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if (err)
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@@ -1951,11 +1992,13 @@ static int attach_recursive_mnt(struct m
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out_cleanup_ids:
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while (!hlist_empty(&tree_list)) {
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child = hlist_entry(tree_list.first, struct mount, mnt_hash);
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+ child->mnt_parent->mnt_ns->pending_mounts = 0;
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umount_tree(child, UMOUNT_SYNC);
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}
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unlock_mount_hash();
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cleanup_group_ids(source_mnt, NULL);
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out:
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+ ns->pending_mounts = 0;
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return err;
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}
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@@ -2758,6 +2801,8 @@ static struct mnt_namespace *alloc_mnt_n
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init_waitqueue_head(&new_ns->poll);
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new_ns->event = 0;
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new_ns->user_ns = get_user_ns(user_ns);
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+ new_ns->mounts = 0;
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+ new_ns->pending_mounts = 0;
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return new_ns;
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}
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@@ -2807,6 +2852,7 @@ struct mnt_namespace *copy_mnt_ns(unsign
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q = new;
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while (p) {
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q->mnt_ns = new_ns;
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+ new_ns->mounts++;
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if (new_fs) {
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if (&p->mnt == new_fs->root.mnt) {
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new_fs->root.mnt = mntget(&q->mnt);
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@@ -2845,6 +2891,7 @@ static struct mnt_namespace *create_mnt_
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struct mount *mnt = real_mount(m);
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mnt->mnt_ns = new_ns;
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new_ns->root = mnt;
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+ new_ns->mounts++;
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list_add(&mnt->mnt_list, &new_ns->list);
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} else {
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mntput(m);
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--- a/fs/pnode.c
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+++ b/fs/pnode.c
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@@ -259,7 +259,7 @@ static int propagate_one(struct mount *m
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read_sequnlock_excl(&mount_lock);
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}
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hlist_add_head(&child->mnt_hash, list);
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- return 0;
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+ return count_mounts(m->mnt_ns, child);
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}
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/*
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--- a/fs/pnode.h
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+++ b/fs/pnode.h
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@@ -52,4 +52,5 @@ void mnt_set_mountpoint(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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--- a/include/linux/mount.h
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+++ b/include/linux/mount.h
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@@ -96,4 +96,6 @@ extern void mark_mounts_for_expiry(struc
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extern dev_t name_to_dev_t(const char *name);
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+extern unsigned int sysctl_mount_max;
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+
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#endif /* _LINUX_MOUNT_H */
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--- a/kernel/sysctl.c
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+++ b/kernel/sysctl.c
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@@ -65,6 +65,7 @@
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#include <linux/sched/sysctl.h>
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#include <linux/kexec.h>
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#include <linux/bpf.h>
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+#include <linux/mount.h>
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#include <asm/uaccess.h>
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#include <asm/processor.h>
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@@ -1850,6 +1851,14 @@ static struct ctl_table fs_table[] = {
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.mode = 0644,
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.proc_handler = proc_doulongvec_minmax,
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},
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+ {
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+ .procname = "mount-max",
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+ .data = &sysctl_mount_max,
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+ .maxlen = sizeof(unsigned int),
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+ .mode = 0644,
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+ .proc_handler = proc_dointvec_minmax,
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+ .extra1 = &one,
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+ },
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{ }
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};
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@ -100,6 +100,7 @@ bugfix/all/fs-Give-dentry-to-inode_change_ok-instead-of-inode.patch
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bugfix/all/fs-Avoid-premature-clearing-of-capabilities.patch
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bugfix/all/mpi-Fix-NULL-ptr-dereference-in-mpi_powm-ver-3.patch
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bugfix/all/vfio-pci-Fix-integer-overflows-bitmask-check.patch
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bugfix/all/mnt-Add-a-per-mount-namespace-limit-on-the-number-of.patch
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# ABI maintenance
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