Subject: CVE-2021-47397: sctp: break out if skb_header_pointer returns NULL in sctp_rcv_ootb

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

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

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

sctp: break out if skb_header_pointer returns NULL in sctp_rcv_ootb

We should always check if skb_header_pointer's return is NULL before
using it, otherwise it may cause null-ptr-deref, as syzbot reported:

  KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
  RIP: 0010:sctp_rcv_ootb net/sctp/input.c:705 [inline]
  RIP: 0010:sctp_rcv+0x1d84/0x3220 net/sctp/input.c:196
  Call Trace:
  <IRQ>
   sctp6_rcv+0x38/0x60 net/sctp/ipv6.c:1109
   ip6_protocol_deliver_rcu+0x2e9/0x1ca0 net/ipv6/ip6_input.c:422
   ip6_input_finish+0x62/0x170 net/ipv6/ip6_input.c:463
   NF_HOOK include/linux/netfilter.h:307 [inline]
   NF_HOOK include/linux/netfilter.h:301 [inline]
   ip6_input+0x9c/0xd0 net/ipv6/ip6_input.c:472
   dst_input include/net/dst.h:460 [inline]
   ip6_rcv_finish net/ipv6/ip6_input.c:76 [inline]
   NF_HOOK include/linux/netfilter.h:307 [inline]
   NF_HOOK include/linux/netfilter.h:301 [inline]
   ipv6_rcv+0x28c/0x3c0 net/ipv6/ip6_input.c:297

The Linux kernel CVE team has assigned CVE-2021-47397 to this issue.

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

	Issue introduced in 4.8 with commit 3acb50c18d8d and fixed in 4.14.249 with commit 77bc7dcf0fcc
	Issue introduced in 4.8 with commit 3acb50c18d8d and fixed in 4.19.209 with commit 8c630a7b4f9d
	Issue introduced in 4.8 with commit 3acb50c18d8d and fixed in 5.4.151 with commit ec018021cf44
	Issue introduced in 4.8 with commit 3acb50c18d8d and fixed in 5.10.71 with commit 9c6591ae8e63
	Issue introduced in 4.8 with commit 3acb50c18d8d and fixed in 5.14.10 with commit 8180611c238e
	Issue introduced in 4.8 with commit 3acb50c18d8d and fixed in 5.15 with commit f7e745f8e944

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-2021-47397
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:
	net/sctp/input.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/77bc7dcf0fcc1519341a91788d7a2914fcfddf6d
	https://git.kernel.org/stable/c/8c630a7b4f9dec63f08bd881ab77984a724a5124
	https://git.kernel.org/stable/c/ec018021cf445abbe8e2f3e2a7f1dcc813cb8ea1
	https://git.kernel.org/stable/c/9c6591ae8e63f93c895ad5e2703c36c548aac997
	https://git.kernel.org/stable/c/8180611c238e11676612eb2a9828b1c7a3a4d77b
	https://git.kernel.org/stable/c/f7e745f8e94492a8ac0b0a26e25f2b19d342918f