linux-cve-announce - CVE-2023-54112: kcm: Fix memory leak in error path of kcm

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Message-ID: <2025122413-CVE-2023-54112-71f7@gregkh>
Date: Wed, 24 Dec 2025 14:07:09 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2023-54112: kcm: Fix memory leak in error path of kcm_sendmsg()

From: Greg Kroah-Hartman <gregkh@...nel.org>

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

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

kcm: Fix memory leak in error path of kcm_sendmsg()

syzbot reported a memory leak like below:

BUG: memory leak
unreferenced object 0xffff88810b088c00 (size 240):
  comm "syz-executor186", pid 5012, jiffies 4294943306 (age 13.680s)
  hex dump (first 32 bytes):
    00 89 08 0b 81 88 ff ff 00 00 00 00 00 00 00 00  ................
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
  backtrace:
    [<ffffffff83e5d5ff>] __alloc_skb+0x1ef/0x230 net/core/skbuff.c:634
    [<ffffffff84606e59>] alloc_skb include/linux/skbuff.h:1289 [inline]
    [<ffffffff84606e59>] kcm_sendmsg+0x269/0x1050 net/kcm/kcmsock.c:815
    [<ffffffff83e479c6>] sock_sendmsg_nosec net/socket.c:725 [inline]
    [<ffffffff83e479c6>] sock_sendmsg+0x56/0xb0 net/socket.c:748
    [<ffffffff83e47f55>] ____sys_sendmsg+0x365/0x470 net/socket.c:2494
    [<ffffffff83e4c389>] ___sys_sendmsg+0xc9/0x130 net/socket.c:2548
    [<ffffffff83e4c536>] __sys_sendmsg+0xa6/0x120 net/socket.c:2577
    [<ffffffff84ad7bb8>] do_syscall_x64 arch/x86/entry/common.c:50 [inline]
    [<ffffffff84ad7bb8>] do_syscall_64+0x38/0xb0 arch/x86/entry/common.c:80
    [<ffffffff84c0008b>] entry_SYSCALL_64_after_hwframe+0x63/0xcd

In kcm_sendmsg(), kcm_tx_msg(head)->last_skb is used as a cursor to append
newly allocated skbs to 'head'. If some bytes are copied, an error occurred,
and jumped to out_error label, 'last_skb' is left unmodified. A later
kcm_sendmsg() will use an obsoleted 'last_skb' reference, corrupting the
'head' frag_list and causing the leak.

This patch fixes this issue by properly updating the last allocated skb in
'last_skb'.

The Linux kernel CVE team has assigned CVE-2023-54112 to this issue.


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

	Issue introduced in 4.6 with commit ab7ac4eb9832e32a09f4e8042705484d2fb0aad3 and fixed in 4.14.326 with commit 8dc7eb757b1652b82725f32e0c89a1e9f6c0e13b
	Issue introduced in 4.6 with commit ab7ac4eb9832e32a09f4e8042705484d2fb0aad3 and fixed in 4.19.295 with commit 5e5554389397e98fafb9efe395d8b4830dd5f042
	Issue introduced in 4.6 with commit ab7ac4eb9832e32a09f4e8042705484d2fb0aad3 and fixed in 5.4.257 with commit 479c71cda14b3c3a6515773faa39055333eaa2b7
	Issue introduced in 4.6 with commit ab7ac4eb9832e32a09f4e8042705484d2fb0aad3 and fixed in 5.10.195 with commit 33db24ad811b3576a0c2f8862506763f2be925b0
	Issue introduced in 4.6 with commit ab7ac4eb9832e32a09f4e8042705484d2fb0aad3 and fixed in 5.15.132 with commit 97275339c34cfbccd65e87bc38fd910ae66c48ba
	Issue introduced in 4.6 with commit ab7ac4eb9832e32a09f4e8042705484d2fb0aad3 and fixed in 6.1.54 with commit 16989de75497574b5fafd174c0c233d5a86858b7
	Issue introduced in 4.6 with commit ab7ac4eb9832e32a09f4e8042705484d2fb0aad3 and fixed in 6.5.4 with commit af8085e0fc3207ecbf8b9e7a635c790e36d058c6
	Issue introduced in 4.6 with commit ab7ac4eb9832e32a09f4e8042705484d2fb0aad3 and fixed in 6.6 with commit c821a88bd720b0046433173185fd841a100d44ad

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-2023-54112
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/kcm/kcmsock.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/8dc7eb757b1652b82725f32e0c89a1e9f6c0e13b
	https://git.kernel.org/stable/c/5e5554389397e98fafb9efe395d8b4830dd5f042
	https://git.kernel.org/stable/c/479c71cda14b3c3a6515773faa39055333eaa2b7
	https://git.kernel.org/stable/c/33db24ad811b3576a0c2f8862506763f2be925b0
	https://git.kernel.org/stable/c/97275339c34cfbccd65e87bc38fd910ae66c48ba
	https://git.kernel.org/stable/c/16989de75497574b5fafd174c0c233d5a86858b7
	https://git.kernel.org/stable/c/af8085e0fc3207ecbf8b9e7a635c790e36d058c6
	https://git.kernel.org/stable/c/c821a88bd720b0046433173185fd841a100d44ad