Subject: CVE-2022-48785: ipv6: mcast: use rcu-safe version of ipv6_get_lladdr()

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

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

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

ipv6: mcast: use rcu-safe version of ipv6_get_lladdr()

Some time ago 8965779d2c0e ("ipv6,mcast: always hold idev->lock before mca_lock")
switched ipv6_get_lladdr() to __ipv6_get_lladdr(), which is rcu-unsafe
version. That was OK, because idev->lock was held for these codepaths.

In 88e2ca308094 ("mld: convert ifmcaddr6 to RCU") these external locks were
removed, so we probably need to restore the original rcu-safe call.

Otherwise, we occasionally get a machine crashed/stalled with the following
in dmesg:

[ 3405.966610][T230589] general protection fault, probably for non-canonical address 0xdead00000000008c: 0000 [#1] SMP NOPTI
[ 3405.982083][T230589] CPU: 44 PID: 230589 Comm: kworker/44:3 Tainted: G           O      5.15.19-cloudflare-2022.2.1 #1
[ 3405.998061][T230589] Hardware name: SUPA-COOL-SERV
[ 3406.009552][T230589] Workqueue: mld mld_ifc_work
[ 3406.017224][T230589] RIP: 0010:__ipv6_get_lladdr+0x34/0x60
[ 3406.025780][T230589] Code: 57 10 48 83 c7 08 48 89 e5 48 39 d7 74 3e 48 8d 82 38 ff ff ff eb 13 48 8b 90 d0 00 00 00 48 8d 82 38 ff ff ff 48 39 d7 74 22 <66> 83 78 32 20 77 1b 75 e4 89 ca 23 50 2c 75 dd 48 8b 50 08 48 8b
[ 3406.055748][T230589] RSP: 0018:ffff94e4b3fc3d10 EFLAGS: 00010202
[ 3406.065617][T230589] RAX: dead00000000005a RBX: ffff94e4b3fc3d30 RCX: 0000000000000040
[ 3406.077477][T230589] RDX: dead000000000122 RSI: ffff94e4b3fc3d30 RDI: ffff8c3a31431008
[ 3406.089389][T230589] RBP: ffff94e4b3fc3d10 R08: 0000000000000000 R09: 0000000000000000
[ 3406.101445][T230589] R10: ffff8c3a31430000 R11: 000000000000000b R12: ffff8c2c37887100
[ 3406.113553][T230589] R13: ffff8c3a39537000 R14: 00000000000005dc R15: ffff8c3a31431000
[ 3406.125730][T230589] FS:  0000000000000000(0000) GS:ffff8c3b9fc80000(0000) knlGS:0000000000000000
[ 3406.138992][T230589] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 3406.149895][T230589] CR2: 00007f0dfea1db60 CR3: 000000387b5f2000 CR4: 0000000000350ee0
[ 3406.162421][T230589] Call Trace:
[ 3406.170235][T230589]  <TASK>
[ 3406.177736][T230589]  mld_newpack+0xfe/0x1a0
[ 3406.186686][T230589]  add_grhead+0x87/0xa0
[ 3406.195498][T230589]  add_grec+0x485/0x4e0
[ 3406.204310][T230589]  ? newidle_balance+0x126/0x3f0
[ 3406.214024][T230589]  mld_ifc_work+0x15d/0x450
[ 3406.223279][T230589]  process_one_work+0x1e6/0x380
[ 3406.232982][T230589]  worker_thread+0x50/0x3a0
[ 3406.242371][T230589]  ? rescuer_thread+0x360/0x360
[ 3406.252175][T230589]  kthread+0x127/0x150
[ 3406.261197][T230589]  ? set_kthread_struct+0x40/0x40
[ 3406.271287][T230589]  ret_from_fork+0x22/0x30
[ 3406.280812][T230589]  </TASK>
[ 3406.288937][T230589] Modules linked in: ... [last unloaded: kheaders]
[ 3406.476714][T230589] ---[ end trace 3525a7655f2f3b9e ]---

The Linux kernel CVE team has assigned CVE-2022-48785 to this issue.

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

	Issue introduced in 5.13 with commit 88e2ca308094 and fixed in 5.15.25 with commit 3e11ef1903cf
	Issue introduced in 5.13 with commit 88e2ca308094 and fixed in 5.16.11 with commit 27f567c84f44
	Issue introduced in 5.13 with commit 88e2ca308094 and fixed in 5.17 with commit 26394fc118d6

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-2022-48785
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/addrconf.h
	net/ipv6/addrconf.c
	net/ipv6/mcast.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/3e11ef1903cf6c2fba35594b193a3570854d9e9e
	https://git.kernel.org/stable/c/27f567c84f446048670376827e356f9c92033bf9
	https://git.kernel.org/stable/c/26394fc118d6115390bd5b3a0fb17096271da227