CVE-2026-89630: smb: client: restore the data_offset bound in is_valid_oplock_break()

CVE-2026-89630: smb: client: restore the data_offset bound in is_valid_oplock_break()

[Greg Kroah-Hartman]

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

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

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

smb: client: restore the data_offset bound in is_valid_oplock_break()

Commit 83bfbd0bb902 ("cifs: Remove the RFC1002 header from smb_hdr")
changed the quantity this bound is measured against.  It used to be
srv->total_read minus the 4-byte RFC1002 preamble that total_read then
included, so it was the SMB message length.  The same commit stopped
counting the preamble, and the mechanical substitution to
srv->total_read - srv->pdu_size left an expression that is identically
zero: standard_receive3() reads MID_HEADER_SIZE() bytes and then exactly
pdu_length - MID_HEADER_SIZE() more, adding both to total_read.

len is therefore 0, the subtraction below it wraps, and no __u32
DataOffset can exceed the result, so the check from commit 097f5863b1a0
("cifs: read overflow in is_valid_oplock_break()") no longer rejects
anything.  Use total_read, which is now the message length on its own.

The Linux kernel CVE team has assigned CVE-2026-89630 to this issue.


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

	Issue introduced in 6.19 with commit 83bfbd0bb9025f98fa62b44f93bd67466773d1db and fixed in 7.2.4 with commit 5b16a1967a01ad4496a7206a87c3eb16f1df2b05
	Issue introduced in 6.19 with commit 83bfbd0bb9025f98fa62b44f93bd67466773d1db and fixed in 7.3-rc1 with commit ba22f575de9deeae4ae0859ca4315a7698226237

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-2026-89630
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/smb1misc.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/5b16a1967a01ad4496a7206a87c3eb16f1df2b05
	https://git.kernel.org/stable/c/ba22f575de9deeae4ae0859ca4315a7698226237