CVE-2026-74430: rxrpc: Fix ACKALL packet handling

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

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

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

rxrpc: Fix ACKALL packet handling

rxrpc_input_ackall() accepts ACKALL packets without checking whether the
call is in a state that can legitimately have outstanding transmit buffers.
A forged ACKALL can therefore reach a new service call in
RXRPC_CALL_SERVER_RECV_REQUEST before any reply packets have been queued.

In that state call->tx_top is zero and call->tx_queue is NULL, so
rxrpc_rotate_tx_window() dereferences a NULL txqueue and triggers a
null-pointer dereference.

Fix the handling of ACKALL packets by the following means:

 (1) Add two new call states: RXRPC_CALL_CLIENT_PRE_SEND which indicates
     that the client call is connected, but nothing has been transmitted as
     yet; and RXRPC_CALL_CLIENT_AWAIT_ACK, which indicates that everything
     has been transmitted at least once, but we're now waiting for the
     stuff remaining in the Tx buffer to be ACK'd (retransmissions may
     still happen).

     The RXRPC_CALL_CLIENT_PRE_SEND state is set when the call is assigned
     a channel and transitions to RXRPC_CALL_CLIENT_SEND_REQUEST when the
     first packet is transmitted.

     RXRPC_CALL_CLIENT_AWAIT_REPLY is then narrowed in scope to indicate
     that all Tx packets have been ACK'd and we're now waiting for the
     reply to be received.

 (2) As per Wyatt Feng's original patch[1], the ACKALL handler then checks
     that the call state is one in which there might be stuff in the Tx
     buffer to ACK, but now this includes AWAIT_ACK rather than
     AWAIT_REPLY.  ACKALL packets are ignored if received in the wrong
     state.

     Note that unlike Wyatt Feng's patch, it's no longer necessary to check
     to see if the Tx buffer exists as this the state set now covers this.

 (3) Make the ACKALL handler use call->tx_transmitted rather than
     call->tx_top as the former is explicitly the highest packet seq number
     transmitted, whereas the latter has a looser definition.

Thanks to Jeffrey Altman for a description of the history of the ACKALL
packet[1].

The Linux kernel CVE team has assigned CVE-2026-74430 to this issue.


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

	Issue introduced in 6.14 with commit b341a0263b1b804d329f864c2dc24815364510ec and fixed in 6.18.40 with commit 8db6a2c95e36938076b37466ce36774526a5c8c3
	Issue introduced in 6.14 with commit b341a0263b1b804d329f864c2dc24815364510ec and fixed in 7.1.5 with commit 523cb585672ae681b2d3b0d620aec5313774e2e2
	Issue introduced in 6.14 with commit b341a0263b1b804d329f864c2dc24815364510ec and fixed in 7.2-rc1 with commit 9b6ce594808580b2a19e6e1aa459ef56c0153ac1

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-2026-74430
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/conn_client.c
	net/rxrpc/input.c
	net/rxrpc/sendmsg.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/8db6a2c95e36938076b37466ce36774526a5c8c3
	https://git.kernel.org/stable/c/523cb585672ae681b2d3b0d620aec5313774e2e2
	https://git.kernel.org/stable/c/9b6ce594808580b2a19e6e1aa459ef56c0153ac1