linux-cve-announce - CVE-2025-38523: cifs: Fix the smbd

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Message-ID: <2025081652-CVE-2025-38523-b126@gregkh>
Date: Sat, 16 Aug 2025 13:13:54 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-38523: cifs: Fix the smbd_response slab to allow usercopy

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

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

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

cifs: Fix the smbd_response slab to allow usercopy

The handling of received data in the smbdirect client code involves using
copy_to_iter() to copy data from the smbd_reponse struct's packet trailer
to a folioq buffer provided by netfslib that encapsulates a chunk of
pagecache.

If, however, CONFIG_HARDENED_USERCOPY=y, this will result in the checks
then performed in copy_to_iter() oopsing with something like the following:

 CIFS: Attempting to mount //172.31.9.1/test
 CIFS: VFS: RDMA transport established
 usercopy: Kernel memory exposure attempt detected from SLUB object 'smbd_response_0000000091e24ea1' (offset 81, size 63)!
 ------------[ cut here ]------------
 kernel BUG at mm/usercopy.c:102!
 ...
 RIP: 0010:usercopy_abort+0x6c/0x80
 ...
 Call Trace:
  <TASK>
  __check_heap_object+0xe3/0x120
  __check_object_size+0x4dc/0x6d0
  smbd_recv+0x77f/0xfe0 [cifs]
  cifs_readv_from_socket+0x276/0x8f0 [cifs]
  cifs_read_from_socket+0xcd/0x120 [cifs]
  cifs_demultiplex_thread+0x7e9/0x2d50 [cifs]
  kthread+0x396/0x830
  ret_from_fork+0x2b8/0x3b0
  ret_from_fork_asm+0x1a/0x30

The problem is that the smbd_response slab's packet field isn't marked as
being permitted for usercopy.

Fix this by passing parameters to kmem_slab_create() to indicate that
copy_to_iter() is permitted from the packet region of the smbd_response
slab objects, less the header space.

The Linux kernel CVE team has assigned CVE-2025-38523 to this issue.


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

	Issue introduced in 6.12 with commit ee4cdf7ba857a894ad1650d6ab77669cbbfa329e and fixed in 6.12.36 with commit 87dcc7e33fc3dcb8ed32333cec016528b5bb6ce4
	Issue introduced in 6.12 with commit ee4cdf7ba857a894ad1650d6ab77669cbbfa329e and fixed in 6.15.8 with commit f0dd353d47f7051afa98c6c60c7486831eb1a410
	Issue introduced in 6.12 with commit ee4cdf7ba857a894ad1650d6ab77669cbbfa329e and fixed in 6.16 with commit 43e7e284fc77b710d899569360ea46fa3374ae22

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-2025-38523
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:
	fs/smb/client/smbdirect.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/87dcc7e33fc3dcb8ed32333cec016528b5bb6ce4
	https://git.kernel.org/stable/c/f0dd353d47f7051afa98c6c60c7486831eb1a410
	https://git.kernel.org/stable/c/43e7e284fc77b710d899569360ea46fa3374ae22