[PATCH 6.1 520/609] sctp: fix addip_serial increment on ASCONF_ACK allocation failure

6.1-stable review patch.  If anyone has any objections, please let me know.

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

From: Qing Luo <[email protected]>

[ Upstream commit aa2e13ae8d3cbe2c15ef4f7e971b2de0832794aa ]

In sctp_process_asconf(), when sctp_make_asconf_ack() fails to allocate
the ASCONF_ACK chunk due to memory pressure, the code jumps to the
done label where asoc->peer.addip_serial is unconditionally incremented.

This leaves the peer's ASCONF (serial N) unacknowledged while the local
endpoint now expects serial N+1. When the peer retransmits serial N, it
falls into the serial < addip_serial + 1 branch ,
which attempts to look up a cached ACK for serial N. No cached ACK
exists since the allocation failed, so the retransmission is silently
discarded. The peer eventually times out and ABORTs the association.

Move the addip_serial increment inside the if (asconf_ack) block so that
the serial number is only advanced when the ASCONF_ACK is successfully
created and cached. This way, on allocation failure, the serial number
is unchanged and the peer's retransmitted ASCONF will be correctly
re-processed.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Qing Luo <[email protected]>
Acked-by: Xin Long <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>
Signed-off-by: Sasha Levin <[email protected]>
---
 net/sctp/sm_make_chunk.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/net/sctp/sm_make_chunk.c b/net/sctp/sm_make_chunk.c
index 837fb8280bfd5..6d738f95aff1d 100644
--- a/net/sctp/sm_make_chunk.c
+++ b/net/sctp/sm_make_chunk.c
@@ -3362,12 +3362,11 @@ struct sctp_chunk *sctp_process_asconf(struct sctp_association *asoc,
 			goto done;
 	}
 done:
-	asoc->peer.addip_serial++;
-
 	/* If we are sending a new ASCONF_ACK hold a reference to it in assoc
 	 * after freeing the reference to old asconf ack if any.
 	 */
 	if (asconf_ack) {
+		asoc->peer.addip_serial++;
 		sctp_chunk_hold(asconf_ack);
 		list_add_tail(&asconf_ack->transmitted_list,
 			      &asoc->asconf_ack_list);
-- 
2.53.0