sctp: leave the err path free in sctp_stream_init to sctp_stream_free

A NULL pointer dereference was reported by Wei Chen:

  BUG: kernel NULL pointer dereference, address: 0000000000000000
  RIP: 0010:__list_del_entry_valid+0x26/0x80
  Call Trace:
   <TASK>
   sctp_sched_dequeue_common+0x1c/0x90
   sctp_sched_prio_dequeue+0x67/0x80
   __sctp_outq_teardown+0x299/0x380
   sctp_outq_free+0x15/0x20
   sctp_association_free+0xc3/0x440
   sctp_do_sm+0x1ca7/0x2210
   sctp_assoc_bh_rcv+0x1f6/0x340

This happens when calling sctp_sendmsg without connecting to server first.
In this case, a data chunk already queues up in send queue of client side
when processing the INIT_ACK from server in sctp_process_init() where it
calls sctp_stream_init() to alloc stream_in. If it fails to alloc stream_in
all stream_out will be freed in sctp_stream_init's err path. Then in the
asoc freeing it will crash when dequeuing this data chunk as stream_out
is missing.

As we can't free stream out before dequeuing all data from send queue, and
this patch is to fix it by moving the err path stream_out/in freeing in
sctp_stream_init() to sctp_stream_free() which is eventually called when
freeing the asoc in sctp_association_free(). This fix also makes the code
in sctp_process_init() more clear.

Note that in sctp_association_init() when it fails in sctp_stream_init(),
sctp_association_free() will not be called, and in that case it should
go to 'stream_free' err path to free stream instead of 'fail_init'.

Fixes: 5bbbbe3 ("sctp: introduce stream scheduler foundations")
Reported-by: Wei Chen <harperchen1110@gmail.com>
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Link: https://lore.kernel.org/r/831a3dc100c4908ff76e5bcc363be97f2778bc0b.1658787066.git.lucien.xin@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: lxin

net/sctp/associola.c

@@ -229,9 +229,8 @@ static struct sctp_association *sctp_association_init(
 	if (!sctp_ulpq_init(&asoc->ulpq, asoc))
 		goto fail_init;
 
-	if (sctp_stream_init(&asoc->stream, asoc->c.sinit_num_ostreams,
-			     0, gfp))
-		goto fail_init;
+	if (sctp_stream_init(&asoc->stream, asoc->c.sinit_num_ostreams, 0, gfp))
+		goto stream_free;
 
 	/* Initialize default path MTU. */
 	asoc->pathmtu = sp->pathmtu;

net/sctp/stream.c

@@ -137,30 +137,17 @@ int sctp_stream_init(struct sctp_stream *stream, __u16 outcnt, __u16 incnt,
 
 	ret = sctp_stream_alloc_out(stream, outcnt, gfp);
 	if (ret)
-		goto out_err;
+		return ret;
 
 	for (i = 0; i < stream->outcnt; i++)
 		SCTP_SO(stream, i)->state = SCTP_STREAM_OPEN;
 
 handle_in:
 	sctp_stream_interleave_init(stream);
 	if (!incnt)
-		goto out;
-
-	ret = sctp_stream_alloc_in(stream, incnt, gfp);
-	if (ret)
-		goto in_err;
-
-	goto out;
+		return 0;
 
-in_err:
-	sched->free(stream);
-	genradix_free(&stream->in);
-out_err:
-	genradix_free(&stream->out);
-	stream->outcnt = 0;
-out:
-	return ret;
+	return sctp_stream_alloc_in(stream, incnt, gfp);
 }
 
 int sctp_stream_init_ext(struct sctp_stream *stream, __u16 sid)