CVE-2026-64026: rxrpc: Fix DATA decrypt vs splice() by copying data to buffer in recvmsg

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

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

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

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

rxrpc: Fix DATA decrypt vs splice() by copying data to buffer in recvmsg

This improves the fix for CVE-2026-43500.

Fix the pagecache corruption from in-place decryption of a DATA packet
transmitted locally by splice() by getting rid of the packet sharing in the
I/O thread and unconditionally extracting the packet content into a bounce
buffer in which the buffer is decrypted.  recvmsg() (or the kernel
equivalent) then copies the data from the bounce buffer to the destination
buffer.  The sk_buff then remains unmodified.

This has an additional advantage in that the packet is then arranged in the
buffer with the correct alignment required for the crypto algorithms to
process directly.  The performance of the crypto does seem to be a little
faster and, surprisingly, the unencrypted performance doesn't seem to
change much - possibly due to removing complexity from the I/O thread.

Yet another advantage is that the I/O thread doesn't have to copy packets
which would slow down packet distribution, ACK generation, etc..

The buffer belongs to the call and is allocated initially at 2K,
sufficiently large to hold a whole jumbo subpacket, but the buffer will be
increased in size if needed.  However, to take this work, MSG_PEEK may
cause a later packet to be decrypted into the buffer, in which case the
earlier one will need re-decrypting for a subsequent recvmsg().

Note that rx_pkt_offset may legitimately see 0 as a valid offset now, so
switch to using USHRT_MAX to indicate an invalid offset.

Note also that I would generally prefer to replace the buffers of the
current sk_buff with a new kmalloc'd buffer of the right size, ditching the
old data and frags as this makes the handling of MSG_PEEK easier and
removes the re-decryption issue, but this looks like quite a complicated
thing to achieve.  skb_morph() looks half way to what I want, but I don't
want to have to allocate a new sk_buff.

The Linux kernel CVE team has assigned CVE-2026-64026 to this issue.


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

	Issue introduced in 5.3 with commit d0d5c0cd1e711c98703f3544c1e6fc1372898de5 and fixed in 6.6.143 with commit a05bf6d9e621fa71e89ccebe3047ba45218d7b38
	Issue introduced in 5.3 with commit d0d5c0cd1e711c98703f3544c1e6fc1372898de5 and fixed in 6.12.93 with commit b94a6ccbaf1104dd980150a65fdeb2f69d17d2f5
	Issue introduced in 5.3 with commit d0d5c0cd1e711c98703f3544c1e6fc1372898de5 and fixed in 6.18.35 with commit 46cb765e2e5ad52303ea157e10d370bb6b7acbbf
	Issue introduced in 5.3 with commit d0d5c0cd1e711c98703f3544c1e6fc1372898de5 and fixed in 7.0.11 with commit c580087743712112778a06d65a4074053072d7bf
	Issue introduced in 5.3 with commit d0d5c0cd1e711c98703f3544c1e6fc1372898de5 and fixed in 7.1 with commit d2bc90cf6c75cb96d2ce549be6c35efa3099d25b

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-2026-64026
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/rxrpc/ar-internal.h
	net/rxrpc/call_event.c
	net/rxrpc/call_object.c
	net/rxrpc/insecure.c
	net/rxrpc/recvmsg.c
	net/rxrpc/rxgk.c
	net/rxrpc/rxgk_common.h
	net/rxrpc/rxkad.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/a05bf6d9e621fa71e89ccebe3047ba45218d7b38
	https://git.kernel.org/stable/c/b94a6ccbaf1104dd980150a65fdeb2f69d17d2f5
	https://git.kernel.org/stable/c/46cb765e2e5ad52303ea157e10d370bb6b7acbbf
	https://git.kernel.org/stable/c/c580087743712112778a06d65a4074053072d7bf
	https://git.kernel.org/stable/c/d2bc90cf6c75cb96d2ce549be6c35efa3099d25b