CVE-2026-89633: smb: client: fix OOB read/write from unvalidated DataOffset in coalesce_t2()

CVE-2026-89633: smb: client: fix OOB read/write from unvalidated DataOffset in coalesce_t2()

[Greg Kroah-Hartman]

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

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

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

smb: client: fix OOB read/write from unvalidated DataOffset in coalesce_t2()

coalesce_t2() computes data pointers directly from server-supplied
DataOffset fields with no validation against buffer bounds:

  data_area_of_tgt = (char *)&pSMBt->hdr.Protocol +
                     get_unaligned_le16(&pSMBt->t2_rsp.DataOffset);
  data_area_of_src = (char *)&pSMBs->hdr.Protocol +
                     get_unaligned_le16(&pSMBs->t2_rsp.DataOffset);
  data_area_of_tgt += total_in_tgt;
  ...
  memcpy(data_area_of_tgt, data_area_of_src, total_in_src);

A small DataOffset can push a pointer below the actual byte area,
overwriting header fields; a large one can push it past the buffer
end, causing out-of-bounds heap reads (source) or writes (target).
The BCC overflow guard does not prevent this: BCC reflects how much
data is present, while DataOffset controls where in the buffer it
starts.

The "validate target area" comment present since the function was
first written in 2005 was a placeholder that was never implemented.

Add lower- and upper-bound checks for both data pointers before the
memcpy, and before any target header fields are modified.

The Linux kernel CVE team has assigned CVE-2026-89633 to this issue.


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

	Issue introduced in 2.6.12 with commit e4eb295d38b57f4d4b956942a48887eb252d97c6 and fixed in 6.18.51 with commit 672cf86aa6aa0fb4012ce4c3b3498df42ad67a4e
	Issue introduced in 2.6.12 with commit e4eb295d38b57f4d4b956942a48887eb252d97c6 and fixed in 7.2.4 with commit 033bc80019f07d158630df4e69b19a49010f54f1
	Issue introduced in 2.6.12 with commit e4eb295d38b57f4d4b956942a48887eb252d97c6 and fixed in 7.3-rc1 with commit 6343c1da561962688f203362d80d6a3bfa39fa1b

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-2026-89633
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/smb1transport.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/672cf86aa6aa0fb4012ce4c3b3498df42ad67a4e
	https://git.kernel.org/stable/c/033bc80019f07d158630df4e69b19a49010f54f1
	https://git.kernel.org/stable/c/6343c1da561962688f203362d80d6a3bfa39fa1b