From: Yuxiang Yang Date: Sun, 9 Aug 2026 04:38:06 +0000 (+0800) Subject: sctp: fix use-after-free of cached ASCONF chunk X-Git-Tag: v7.2~27^2~3 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=8c283e7b56adce00193837f3311b06662466fb21;p=thirdparty%2Fkernel%2Flinux.git sctp: fix use-after-free of cached ASCONF chunk addip_last_asconf caches the outstanding outbound ASCONF chunk. The normal ASCONF-ACK completion path releases the chunk and clears the pointer. However, sctp_asconf_queue_teardown() releases the cached chunk without clearing addip_last_asconf. During peer restart handling, sctp_sf_do_dupcook_a() queues SCTP_CMD_PURGE_ASCONF_QUEUE, which invokes sctp_asconf_queue_teardown() while the association remains alive and leaves the pointer dangling. A delayed authenticated ASCONF-ACK can then reach sctp_sf_do_asconf_ack(), which accesses the stale chunk and passes it to sctp_process_asconf_ack(), causing a use-after-free and a second release. Clearing the pointer exposes a race with T4 expiry. Peer restart handling queues the timer stop before the purge, but SCTP_CMD_TIMER_STOP uses timer_delete(), which does not wait for a callback already running on another CPU. Such a callback can reach sctp_sf_t4_timer_expire() after the purge and dereference NULL. Clear addip_last_asconf after releasing the cached chunk, and make sctp_sf_t4_timer_expire() consume a stale T4 expiry if no outstanding ASCONF remains. Fixes: a000c01e60e4 ("sctp: stop pending timers and purge queues when peer restart asoc") Cc: stable@vger.kernel.org Suggested-by: Xin Long Signed-off-by: Yuxiang Yang Acked-by: Xin Long Link: https://patch.msgid.link/20260809043806.2768302-1-yangyx22@mails.tsinghua.edu.cn Signed-off-by: Jakub Kicinski --- diff --git a/net/sctp/associola.c b/net/sctp/associola.c index c65c83638cce..5be0bed2685e 100644 --- a/net/sctp/associola.c +++ b/net/sctp/associola.c @@ -1716,6 +1716,8 @@ void sctp_asconf_queue_teardown(struct sctp_association *asoc) sctp_assoc_free_asconf_queue(asoc); /* Free any cached ASCONF chunk. */ - if (asoc->addip_last_asconf) + if (asoc->addip_last_asconf) { sctp_chunk_free(asoc->addip_last_asconf); + asoc->addip_last_asconf = NULL; + } } diff --git a/net/sctp/sm_statefuns.c b/net/sctp/sm_statefuns.c index 708fa07d5fff..3a8e16b29660 100644 --- a/net/sctp/sm_statefuns.c +++ b/net/sctp/sm_statefuns.c @@ -6145,8 +6145,12 @@ enum sctp_disposition sctp_sf_t4_timer_expire( struct sctp_cmd_seq *commands) { struct sctp_chunk *chunk = asoc->addip_last_asconf; - struct sctp_transport *transport = chunk->transport; + struct sctp_transport *transport; + + if (!chunk) + return SCTP_DISPOSITION_CONSUME; + transport = chunk->transport; SCTP_INC_STATS(net, SCTP_MIB_T4_RTO_EXPIREDS); /* ADDIP 4.1 B1) Increment the error counters and perform path failure