[PATCH net 1/1] sctp: stream: fully roll back denied add-stream state

From: Wyatt Feng <[email protected]>

When ADD_OUT_STREAMS is denied, SCTP only shrinks the queued chunks and
then lowers outcnt. That leaves removed stream metadata behind, so a
later re-add can reuse a stale ext and hit a null-pointer dereference in
the scheduler get path.

Fix the rollback by tearing down the removed stream state the same way
other stream resizes do. Unschedule the current scheduler state, clear
out_curr if it still points at a removed stream, drop the removed stream
ext state with sctp_stream_outq_migrate(), and then reschedule the
remaining streams.

This keeps scheduler-private RR/FC/PRIO lists consistent while fully
rolling back denied outgoing stream additions.

Fixes: 637784ade221 ("sctp: introduce priority based stream scheduler")
Cc: [email protected]
Reported-by: Yuan Tan <[email protected]>
Reported-by: Yifan Wu <[email protected]>
Reported-by: Juefei Pu <[email protected]>
Reported-by: Zhengchuan Liang <[email protected]>
Reported-by: Xin Liu <[email protected]>
Assisted-by: Codex:GPT-5.4
Signed-off-by: Wyatt Feng <[email protected]>
Signed-off-by: Ren Wei <[email protected]>
---
 net/sctp/stream.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/net/sctp/stream.c b/net/sctp/stream.c
index c2247793c88b..5c07c6148228 100644
--- a/net/sctp/stream.c
+++ b/net/sctp/stream.c
@@ -1037,6 +1037,7 @@ struct sctp_chunk *sctp_process_strreset_resp(
 		*evp = sctp_ulpevent_make_assoc_reset_event(asoc, flags,
 			stsn, rtsn, GFP_ATOMIC);
 	} else if (req->type == SCTP_PARAM_RESET_ADD_OUT_STREAMS) {
+		const struct sctp_sched_ops *sched;
 		struct sctp_strreset_addstrm *addstrm;
 		__u16 number;
 
@@ -1048,7 +1049,16 @@ struct sctp_chunk *sctp_process_strreset_resp(
 			for (i = number; i < stream->outcnt; i++)
 				SCTP_SO(stream, i)->state = SCTP_STREAM_OPEN;
 		} else {
-			sctp_stream_shrink_out(stream, number);
+			sched = sctp_sched_ops_from_stream(stream);
+			sched->unsched_all(stream);
+			if (stream->out_curr)
+				for (i = number; i < stream->outcnt; i++)
+					if (stream->out_curr == SCTP_SO(stream, i)) {
+						stream->out_curr = NULL;
+						break;
+					}
+			sctp_stream_outq_migrate(stream, NULL, number);
+			sched->sched_all(stream);
 			stream->outcnt = number;
 		}
 
-- 
2.43.7