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sctp: fix use-after-free of cached ASCONF chunk

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commit 8c283e7b56 upstream.

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: a000c01e60 ("sctp: stop pending timers and purge queues when peer restart asoc")
Cc: stable@vger.kernel.org
Suggested-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: Yuxiang Yang <yangyx22@mails.tsinghua.edu.cn>
Acked-by: Xin Long <lucien.xin@gmail.com>
Link: https://patch.msgid.link/20260809043806.2768302-1-yangyx22@mails.tsinghua.edu.cn
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Yuxiang Yang
2026-08-19 18:13:14 +02:00
committed by Greg Kroah-Hartman
parent 1adf929121
commit dc67d528c2
2 changed files with 8 additions and 2 deletions
Download Patch File Download Diff File Expand all files Collapse all files
net/sctp/associola.c
+3 -1
View File
@@ -1731,6 +1731,8 @@ 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;
}
}
net/sctp/sm_statefuns.c
+5 -1
View File
@@ -6109,8 +6109,12 @@ 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