CVE-2024-26615: net/smc: fix illegal rmb_desc access in SMC-D connection dump

[Lee Jones <lee@kernel.org>]

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

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

net/smc: fix illegal rmb_desc access in SMC-D connection dump

A crash was found when dumping SMC-D connections. It can be reproduced
by following steps:

- run nginx/wrk test:
  smc_run nginx
  smc_run wrk -t 16 -c 1000 -d <duration> -H 'Connection: Close' <URL>

- continuously dump SMC-D connections in parallel:
  watch -n 1 'smcss -D'

 BUG: kernel NULL pointer dereference, address: 0000000000000030
 CPU: 2 PID: 7204 Comm: smcss Kdump: loaded Tainted: G	E      6.7.0+ #55
 RIP: 0010:__smc_diag_dump.constprop.0+0x5e5/0x620 [smc_diag]
 Call Trace:
  <TASK>
  ? __die+0x24/0x70
  ? page_fault_oops+0x66/0x150
  ? exc_page_fault+0x69/0x140
  ? asm_exc_page_fault+0x26/0x30
  ? __smc_diag_dump.constprop.0+0x5e5/0x620 [smc_diag]
  ? __kmalloc_node_track_caller+0x35d/0x430
  ? __alloc_skb+0x77/0x170
  smc_diag_dump_proto+0xd0/0xf0 [smc_diag]
  smc_diag_dump+0x26/0x60 [smc_diag]
  netlink_dump+0x19f/0x320
  __netlink_dump_start+0x1dc/0x300
  smc_diag_handler_dump+0x6a/0x80 [smc_diag]
  ? __pfx_smc_diag_dump+0x10/0x10 [smc_diag]
  sock_diag_rcv_msg+0x121/0x140
  ? __pfx_sock_diag_rcv_msg+0x10/0x10
  netlink_rcv_skb+0x5a/0x110
  sock_diag_rcv+0x28/0x40
  netlink_unicast+0x22a/0x330
  netlink_sendmsg+0x1f8/0x420
  __sock_sendmsg+0xb0/0xc0
  ____sys_sendmsg+0x24e/0x300
  ? copy_msghdr_from_user+0x62/0x80
  ___sys_sendmsg+0x7c/0xd0
  ? __do_fault+0x34/0x160
  ? do_read_fault+0x5f/0x100
  ? do_fault+0xb0/0x110
  ? __handle_mm_fault+0x2b0/0x6c0
  __sys_sendmsg+0x4d/0x80
  do_syscall_64+0x69/0x180
  entry_SYSCALL_64_after_hwframe+0x6e/0x76

It is possible that the connection is in process of being established
when we dump it. Assumed that the connection has been registered in a
link group by smc_conn_create() but the rmb_desc has not yet been
initialized by smc_buf_create(), thus causing the illegal access to
conn->rmb_desc. So fix it by checking before dump.

The Linux kernel CVE team has assigned CVE-2024-26615 to this issue.


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

	Issue introduced in 4.19 with commit 4b1b7d3b30a6 and fixed in 4.19.307 with commit 27aea6483891
	Issue introduced in 4.19 with commit 4b1b7d3b30a6 and fixed in 5.4.269 with commit 1fea9969b81c
	Issue introduced in 4.19 with commit 4b1b7d3b30a6 and fixed in 5.10.210 with commit 5fed92ca32ea
	Issue introduced in 4.19 with commit 4b1b7d3b30a6 and fixed in 5.15.149 with commit 68b888d51ac8
	Issue introduced in 4.19 with commit 4b1b7d3b30a6 and fixed in 6.1.76 with commit 6994dba06321
	Issue introduced in 4.19 with commit 4b1b7d3b30a6 and fixed in 6.6.15 with commit a164c2922675
	Issue introduced in 4.19 with commit 4b1b7d3b30a6 and fixed in 6.7.3 with commit 8f3f9186e5bb
	Issue introduced in 4.19 with commit 4b1b7d3b30a6 and fixed in 6.8-rc2 with commit dbc153fd3c14

Please see https://www.kernel.org or 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-2024-26615
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/smc/smc_diag.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/27aea64838914c6122db5b8bd4bed865c9736f22
	https://git.kernel.org/stable/c/1fea9969b81c67d0cb1611d1b8b7d19049d937be
	https://git.kernel.org/stable/c/5fed92ca32eafbfae8b6bee8ca34cca71c6a8b6d
	https://git.kernel.org/stable/c/68b888d51ac82f2b96bf5e077a31d76afcdef25a
	https://git.kernel.org/stable/c/6994dba06321e3c48fdad0ba796a063d9d82183a
	https://git.kernel.org/stable/c/a164c2922675d7051805cdaf2b07daffe44f20d9
	https://git.kernel.org/stable/c/8f3f9186e5bb96a9c9654c41653210e3ea7e48a6
	https://git.kernel.org/stable/c/dbc153fd3c142909e564bb256da087e13fbf239c