CVE-2026-63995: ethtool: cmis: validate start_cmd_payload_size from module

From: Greg Kroah-Hartman <[email protected]>

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

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

ethtool: cmis: validate start_cmd_payload_size from module

The CMIS firmware update code reads start_cmd_payload_size from
the module's FW Management Features CDB reply and uses it directly
as the byte count for memcpy. The destination buffer is 112 bytes
(ETHTOOL_CMIS_CDB_LPL_MAX_PL_LENGTH - 8). So a malicious
module (or corrupted response) can cause a OOB write later on in
cmis_fw_update_start_download().

Let's error out. If modules that expect longer LPL writes actually
exist we should revisit.

struct cmis_cdb_start_fw_download_pl's definition has to move,
no change there.

The Linux kernel CVE team has assigned CVE-2026-63995 to this issue.


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

	Issue introduced in 6.11 with commit c4f78134d45c9619339c96b4bea380b1d0699788 and fixed in 6.12.93 with commit 63112b4515469d00008452d9cfe3fb3bf1aa2df3
	Issue introduced in 6.11 with commit c4f78134d45c9619339c96b4bea380b1d0699788 and fixed in 6.18.35 with commit 0696709e951be54c699664adf546d16e28974d53
	Issue introduced in 6.11 with commit c4f78134d45c9619339c96b4bea380b1d0699788 and fixed in 7.0.12 with commit a46340da00385be7fb16c62425ebc20006f2d5d8
	Issue introduced in 6.11 with commit c4f78134d45c9619339c96b4bea380b1d0699788 and fixed in 7.1 with commit 12c2496a71f82f63617971ca9b730dffa05cf58b

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-2026-63995
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/ethtool/cmis_fw_update.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/63112b4515469d00008452d9cfe3fb3bf1aa2df3
	https://git.kernel.org/stable/c/0696709e951be54c699664adf546d16e28974d53
	https://git.kernel.org/stable/c/a46340da00385be7fb16c62425ebc20006f2d5d8
	https://git.kernel.org/stable/c/12c2496a71f82f63617971ca9b730dffa05cf58b