Subject: CVE-2022-48719: net, neigh: Do not trigger immediate probes on NUD_FAILED from neigh_managed_work

From: Greg Kroah-Hartman <[email-masked]>

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

net, neigh: Do not trigger immediate probes on NUD_FAILED from neigh_managed_work

syzkaller was able to trigger a deadlock for NTF_MANAGED entries [0]:

  kworker/0:16/14617 is trying to acquire lock:
  ffffffff8d4dd370 (&tbl->lock){++-.}-{2:2}, at: ___neigh_create+0x9e1/0x2990 net/core/neighbour.c:652
  [...]
  but task is already holding lock:
  ffffffff8d4dd370 (&tbl->lock){++-.}-{2:2}, at: neigh_managed_work+0x35/0x250 net/core/neighbour.c:1572

The neighbor entry turned to NUD_FAILED state, where __neigh_event_send()
triggered an immediate probe as per commit cd28ca0a3dd1 ("neigh: reduce
arp latency") via neigh_probe() given table lock was held.

One option to fix this situation is to defer the neigh_probe() back to
the neigh_timer_handler() similarly as pre cd28ca0a3dd1. For the case
of NTF_MANAGED, this deferral is acceptable given this only happens on
actual failure state and regular / expected state is NUD_VALID with the
entry already present.

The fix adds a parameter to __neigh_event_send() in order to communicate
whether immediate probe is allowed or disallowed. Existing call-sites
of neigh_event_send() default as-is to immediate probe. However, the
neigh_managed_work() disables it via use of neigh_event_send_probe().

[0] <TASK>
  __dump_stack lib/dump_stack.c:88 [inline]
  dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106
  print_deadlock_bug kernel/locking/lockdep.c:2956 [inline]
  check_deadlock kernel/locking/lockdep.c:2999 [inline]
  validate_chain kernel/locking/lockdep.c:3788 [inline]
  __lock_acquire.cold+0x149/0x3ab kernel/locking/lockdep.c:5027
  lock_acquire kernel/locking/lockdep.c:5639 [inline]
  lock_acquire+0x1ab/0x510 kernel/locking/lockdep.c:5604
  __raw_write_lock_bh include/linux/rwlock_api_smp.h:202 [inline]
  _raw_write_lock_bh+0x2f/0x40 kernel/locking/spinlock.c:334
  ___neigh_create+0x9e1/0x2990 net/core/neighbour.c:652
  ip6_finish_output2+0x1070/0x14f0 net/ipv6/ip6_output.c:123
  __ip6_finish_output net/ipv6/ip6_output.c:191 [inline]
  __ip6_finish_output+0x61e/0xe90 net/ipv6/ip6_output.c:170
  ip6_finish_output+0x32/0x200 net/ipv6/ip6_output.c:201
  NF_HOOK_COND include/linux/netfilter.h:296 [inline]
  ip6_output+0x1e4/0x530 net/ipv6/ip6_output.c:224
  dst_output include/net/dst.h:451 [inline]
  NF_HOOK include/linux/netfilter.h:307 [inline]
  ndisc_send_skb+0xa99/0x17f0 net/ipv6/ndisc.c:508
  ndisc_send_ns+0x3a9/0x840 net/ipv6/ndisc.c:650
  ndisc_solicit+0x2cd/0x4f0 net/ipv6/ndisc.c:742
  neigh_probe+0xc2/0x110 net/core/neighbour.c:1040
  __neigh_event_send+0x37d/0x1570 net/core/neighbour.c:1201
  neigh_event_send include/net/neighbour.h:470 [inline]
  neigh_managed_work+0x162/0x250 net/core/neighbour.c:1574
  process_one_work+0x9ac/0x1650 kernel/workqueue.c:2307
  worker_thread+0x657/0x1110 kernel/workqueue.c:2454
  kthread+0x2e9/0x3a0 kernel/kthread.c:377
  ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
  </TASK>

The Linux kernel CVE team has assigned CVE-2022-48719 to this issue.

Affected and fixed versions
===========================

	Issue introduced in 5.16 with commit 7482e3841d52 and fixed in 5.16.8 with commit 203a35ebb49c
	Issue introduced in 5.16 with commit 7482e3841d52 and fixed in 5.17 with commit 4a81f6da9cb2

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2022-48719
will be updated if fixes are backported, please check that for the most
up to date information about this issue.

Affected files
==============

The file(s) affected by this issue are:
	include/net/neighbour.h
	net/core/neighbour.c

Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/203a35ebb49cdce377416b0690215d3ce090d364
	https://git.kernel.org/stable/c/4a81f6da9cb2d1ef911131a6fd8bd15cb61fc772