CVE-2026-43362: smb: client: fix in-place encryption corruption in SMB2_write()

CVE-2026-43362: smb: client: fix in-place encryption corruption in SMB2_write()

[Greg Kroah-Hartman]

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

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

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

smb: client: fix in-place encryption corruption in SMB2_write()

SMB2_write() places write payload in iov[1..n] as part of rq_iov.
smb3_init_transform_rq() pointer-shares rq_iov, so crypt_message()
encrypts iov[1] in-place, replacing the original plaintext with
ciphertext. On a replayable error, the retry sends the same iov[1]
which now contains ciphertext instead of the original data,
resulting in corruption.

The corruption is most likely to be observed when connections are
unstable, as reconnects trigger write retries that re-send the
already-encrypted data.

This affects SFU mknod, MF symlinks, etc. On kernels before
6.10 (prior to the netfs conversion), sync writes also used
this path and were similarly affected. The async write path
wasn't unaffected as it uses rq_iter which gets deep-copied.

Fix by moving the write payload into rq_iter via iov_iter_kvec(),
so smb3_init_transform_rq() deep-copies it before encryption.

The Linux kernel CVE team has assigned CVE-2026-43362 to this issue.


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

	Fixed in 6.6.130 with commit 438e77435aee2894d5edf90be5c87004a57f6258
	Fixed in 6.12.78 with commit 52327268224fb9ccc7ecfbbdfdfff54b6e93c518
	Fixed in 6.18.19 with commit 92e64f1852f455f57d0850989e57c30d7fac7d95
	Fixed in 6.19.9 with commit aea5e37388a080361110ab5790f57ae0af383650
	Fixed in 7.0 with commit d78840a6a38d312dc1a51a65317bb67e46f0b929

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-2026-43362
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/smb2pdu.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/438e77435aee2894d5edf90be5c87004a57f6258
	https://git.kernel.org/stable/c/52327268224fb9ccc7ecfbbdfdfff54b6e93c518
	https://git.kernel.org/stable/c/92e64f1852f455f57d0850989e57c30d7fac7d95
	https://git.kernel.org/stable/c/aea5e37388a080361110ab5790f57ae0af383650
	https://git.kernel.org/stable/c/d78840a6a38d312dc1a51a65317bb67e46f0b929