From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: stable@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	patches@lists.linux.dev,
	Daniele Linguaglossa <danielelinguaglossa@gmail.com>,
	Xin Long <lucien.xin@gmail.com>,
	Jakub Kicinski <kuba@kernel.org>,
	Sasha Levin <sashal@kernel.org>
Subject: [PATCH 6.6 057/156] sctp: clear control chunk transport if it is being removed
Date: Mon, 17 Aug 2026 15:33:11 +0200
Message-ID: <20260817132536.818966981@linuxfoundation.org>
In-Reply-To: <20260817132534.666299318@linuxfoundation.org>
References: <20260817132534.666299318@linuxfoundation.org>
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6.6-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Xin Long <lucien.xin@gmail.com>

[ Upstream commit c9158ceaf27780ef64534ad72f44ffde3f8ccc49 ]

sctp_make_heartbeat_ack() caches the destination transport in
chunk->transport without taking a reference. When src_out_of_asoc_ok is
enabled, the HEARTBEAT ACK may remain queued on control_chunk_list instead
of being transmitted immediately.

If the peer transport is removed while the chunk is still queued,
sctp_assoc_rm_peer() drops the transport and schedules it for RCU freeing,
but only clears cached transport pointers in out_chunk_list.  The queued
control chunk therefore retains a dangling transport pointer.

Once an ASCONF_ACK clears the suppression and the queued control chunk is
transmitted, SCTP dereferences the stale transport pointer, leading to a
use-after-free.

Fix this by also clearing chunk->transport for queued control chunks in
control_chunk_list when removing the transport.

Fixes: 8a07eb0a50ae ("sctp: Add ASCONF operation on the single-homed host")
Reported-by: Daniele Linguaglossa <danielelinguaglossa@gmail.com>
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Link: https://patch.msgid.link/7e1168cb722132152a29d47e5eafaeac4a3bf6f3.1785943120.git.lucien.xin@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 net/sctp/associola.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/net/sctp/associola.c b/net/sctp/associola.c
index 44f06c5f1f256..ebdc48be47813 100644
--- a/net/sctp/associola.c
+++ b/net/sctp/associola.c
@@ -573,6 +573,10 @@ void sctp_assoc_rm_peer(struct sctp_association *asoc,
 		if (ch->transport == peer)
 			ch->transport = NULL;
 
+	list_for_each_entry(ch, &asoc->outqueue.control_chunk_list, list)
+		if (ch->transport == peer)
+			ch->transport = NULL;
+
 	asoc->peer.transport_count--;
 
 	sctp_ulpevent_notify_peer_addr_change(peer, SCTP_ADDR_REMOVED, 0);
-- 
2.53.0