Merge branch 'sctp-fix-a-null-pointer-dereference-in-sctp_sched_dequeue_common'

Xin Long says:

====================
sctp: fix a NULL pointer dereference in sctp_sched_dequeue_common

This issue was triggered with SCTP_PR_SCTP_PRIO in sctp,
and caused by not checking and fixing stream->out_curr
after removing a chunk from this stream.

Patch 1 removes an unnecessary check and makes the real
fix easier to add in Patch 2.
====================

Link: https://lore.kernel.org/r/cover.1667598261.git.lucien.xin@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: kuba-moo

net/sctp/outqueue.c

@@ -384,6 +384,7 @@ static int sctp_prsctp_prune_unsent(struct sctp_association *asoc,
 {
 	struct sctp_outq *q = &asoc->outqueue;
 	struct sctp_chunk *chk, *temp;
+	struct sctp_stream_out *sout;
 
 	q->sched->unsched_all(&asoc->stream);
 
@@ -398,12 +399,14 @@ static int sctp_prsctp_prune_unsent(struct sctp_association *asoc,
 		sctp_sched_dequeue_common(q, chk);
 		asoc->sent_cnt_removable--;
 		asoc->abandoned_unsent[SCTP_PR_INDEX(PRIO)]++;
-		if (chk->sinfo.sinfo_stream < asoc->stream.outcnt) {
-			struct sctp_stream_out *streamout =
-				SCTP_SO(&asoc->stream, chk->sinfo.sinfo_stream);
 
-			streamout->ext->abandoned_unsent[SCTP_PR_INDEX(PRIO)]++;
-		}
+		sout = SCTP_SO(&asoc->stream, chk->sinfo.sinfo_stream);
+		sout->ext->abandoned_unsent[SCTP_PR_INDEX(PRIO)]++;
+
+		/* clear out_curr if all frag chunks are pruned */
+		if (asoc->stream.out_curr == sout &&
+		    list_is_last(&chk->frag_list, &chk->msg->chunks))
+			asoc->stream.out_curr = NULL;
 
 		msg_len -= chk->skb->truesize + sizeof(struct sctp_chunk);
 		sctp_chunk_free(chk);