[PATCH 6.1 602/609] sctp: keep chunk->transport in step with the list it is queued on

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

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

From: Baul Lee <[email protected]>

commit 9f2cf069a9a72a2d6b97ca8b4c70e714aac99749 upstream.

__sctp_outq_flush_rtx() moves a gap-acked chunk onto another transport's
transmitted list without updating chunk->transport:

	if (chunk->tsn_gap_acked) {
		list_move_tail(&chunk->transmitted_list,
			       &transport->transmitted);
		continue;
	}

The chunk then sits on a live transport's list while chunk->transport still
names a different one.  If that transport is removed - sctp_assoc_rm_peer()
from an ASCONF Delete-IP - sctp_transport_free() RCU-frees it and the chunk
is left with a dangling pointer.  sctp_assoc_rm_peer() scrubs
peer->transmitted and asoc->outqueue.out_chunk_list, but the chunk is on
neither.

The pointer is not followed while tsn_gap_acked is set.  A SACK that
reneges on the TSN clears the flag, and the next SACK reaches

	tchunk->transport->flight_size -= sctp_data_size(tchunk);

inside the freed transport.  KASAN reports a slab-use-after-free read in
sctp_check_transmitted(), freed from sctp_assoc_rm_peer().  Both the
removal and the SACKs come from the association peer.

Set chunk->transport at the move.  The ordinary resend path needs nothing:
it reaches its list_move_tail() only after sctp_packet_append_chunk()
returned SCTP_XMIT_OK, and __sctp_packet_append_chunk() has rebound the
chunk by then.

Discovered by XBOW, triaged by Baul Lee <[email protected]>

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: [email protected]
Signed-off-by: Baul Lee <[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: Greg Kroah-Hartman <[email protected]>
---
 net/sctp/outqueue.c |    1 +
 1 file changed, 1 insertion(+)

--- a/net/sctp/outqueue.c
+++ b/net/sctp/outqueue.c
@@ -650,6 +650,7 @@ static int __sctp_outq_flush_rtx(struct
 		if (chunk->tsn_gap_acked) {
 			list_move_tail(&chunk->transmitted_list,
 				       &transport->transmitted);
+			chunk->transport = transport;
 			continue;
 		}