Subject: CVE-2021-46999: sctp: do asoc update earlier in sctp_sf_do_dupcook_a

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

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

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

sctp: do asoc update earlier in sctp_sf_do_dupcook_a

There's a panic that occurs in a few of envs, the call trace is as below:

  [] general protection fault, ... 0x29acd70f1000a: 0000 [#1] SMP PTI
  [] RIP: 0010:sctp_ulpevent_notify_peer_addr_change+0x4b/0x1fa [sctp]
  []  sctp_assoc_control_transport+0x1b9/0x210 [sctp]
  []  sctp_do_8_2_transport_strike.isra.16+0x15c/0x220 [sctp]
  []  sctp_cmd_interpreter.isra.21+0x1231/0x1a10 [sctp]
  []  sctp_do_sm+0xc3/0x2a0 [sctp]
  []  sctp_generate_timeout_event+0x81/0xf0 [sctp]

This is caused by a transport use-after-free issue. When processing a
duplicate COOKIE-ECHO chunk in sctp_sf_do_dupcook_a(), both COOKIE-ACK
and SHUTDOWN chunks are allocated with the transort from the new asoc.
However, later in the sideeffect machine, the old asoc is used to send
them out and old asoc's shutdown_last_sent_to is set to the transport
that SHUTDOWN chunk attached to in sctp_cmd_setup_t2(), which actually
belongs to the new asoc. After the new_asoc is freed and the old asoc
T2 timeout, the old asoc's shutdown_last_sent_to that is already freed
would be accessed in sctp_sf_t2_timer_expire().

Thanks Alexander and Jere for helping dig into this issue.

To fix it, this patch is to do the asoc update first, then allocate
the COOKIE-ACK and SHUTDOWN chunks with the 'updated' old asoc. This
would make more sense, as a chunk from an asoc shouldn't be sent out
with another asoc. We had fixed quite a few issues caused by this.

The Linux kernel CVE team has assigned CVE-2021-46999 to this issue.

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

	Issue introduced in 4.19.123 with commit db8bf823e70f and fixed in 4.19.191 with commit d624f2991b97
	Issue introduced in 5.4.41 with commit a204d577be70 and fixed in 5.4.120 with commit b1b31948c0af
	Issue introduced in 5.7 with commit 145cb2f7177d and fixed in 5.10.38 with commit f01988ecf365
	Issue introduced in 5.7 with commit 145cb2f7177d and fixed in 5.11.22 with commit 61b877bad9bb
	Issue introduced in 5.7 with commit 145cb2f7177d and fixed in 5.12.5 with commit 0bfd913c2121
	Issue introduced in 5.7 with commit 145cb2f7177d and fixed in 5.13 with commit 35b4f24415c8
	Issue introduced in 5.6.13 with commit a5ce8531ea50

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-2021-46999
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/sm_statefuns.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/d624f2991b977821375fbd56c91b0c91d456a697
	https://git.kernel.org/stable/c/b1b31948c0af44628e43353828453461bb74098f
	https://git.kernel.org/stable/c/f01988ecf3654f805282dce2d3bb9afe68d2691e
	https://git.kernel.org/stable/c/61b877bad9bb0d82b7d8841be50872557090a704
	https://git.kernel.org/stable/c/0bfd913c2121b3d553bfd52810fe6061d542d625
	https://git.kernel.org/stable/c/35b4f24415c854cd718ccdf38dbea6297f010aae