Subject: CVE-2024-26731: bpf, sockmap: Fix NULL pointer dereference in sk_psock_verdict_data_ready()

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

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

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

bpf, sockmap: Fix NULL pointer dereference in sk_psock_verdict_data_ready()

syzbot reported the following NULL pointer dereference issue [1]:

  BUG: kernel NULL pointer dereference, address: 0000000000000000
  [...]
  RIP: 0010:0x0
  [...]
  Call Trace:
   <TASK>
   sk_psock_verdict_data_ready+0x232/0x340 net/core/skmsg.c:1230
   unix_stream_sendmsg+0x9b4/0x1230 net/unix/af_unix.c:2293
   sock_sendmsg_nosec net/socket.c:730 [inline]
   __sock_sendmsg+0x221/0x270 net/socket.c:745
   ____sys_sendmsg+0x525/0x7d0 net/socket.c:2584
   ___sys_sendmsg net/socket.c:2638 [inline]
   __sys_sendmsg+0x2b0/0x3a0 net/socket.c:2667
   do_syscall_64+0xf9/0x240
   entry_SYSCALL_64_after_hwframe+0x6f/0x77

If sk_psock_verdict_data_ready() and sk_psock_stop_verdict() are called
concurrently, psock->saved_data_ready can be NULL, causing the above issue.

This patch fixes this issue by calling the appropriate data ready function
using the sk_psock_data_ready() helper and protecting it from concurrency
with sk->sk_callback_lock.

The Linux kernel CVE team has assigned CVE-2024-26731 to this issue.

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

	Issue introduced in 6.1.32 with commit dd628fc697ee and fixed in 6.1.80 with commit 4588b13abcbd
	Issue introduced in 6.4 with commit 6df7f764cd3c and fixed in 6.6.19 with commit 9b099ed46dca
	Issue introduced in 6.4 with commit 6df7f764cd3c and fixed in 6.7.7 with commit d61608a4e394
	Issue introduced in 6.4 with commit 6df7f764cd3c and fixed in 6.8 with commit 4cd12c6065df
	Issue introduced in 6.3.6 with commit d3cbd7c57144

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-2024-26731
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/core/skmsg.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/4588b13abcbd561ec67f5b3c1cb2eff690990a54
	https://git.kernel.org/stable/c/9b099ed46dcaf1403c531ff02c3d7400fa37fa26
	https://git.kernel.org/stable/c/d61608a4e394f23e0dca099df9eb8e555453d949
	https://git.kernel.org/stable/c/4cd12c6065dfcdeba10f49949bffcf383b3952d8