[PATCH net v3 2/2] sctp: fix stream->outcnt underflow on duplicate RECONF responses

[Jun Yang <juny24602@gmail.com>]

A cached RECONF chunk may contain more than one request parameter.  A
duplicate response can therefore find and process the same ADD_OUT request
again while another parameter is still outstanding, rolling back outcnt
twice and possibly underflowing it.

Track outstanding request types as bits and clear each bit after its first
response.  Later responses for the same request are then ignored.

Fixes: 11ae76e67a17 ("sctp: implement receiver-side procedures for the Reconf Response Parameter")
Cc: stable@kernel.org
Reported-by: TencentOS Corvus AI <corvus@tencent.com>
Link: https://lore.kernel.org/netdev/20260730110225.37371-1-juny24602@gmail.com/
Suggested-by: Xin Long <lucien.xin@gmail.com>
Assisted-by: tencentos-corvus-ai:kimi-k3
Signed-off-by: Jun Yang <junvyyang@tencent.com>
---
v3:
 - Split the response_seq == 0 lookup fix into patch 1 (Simon Horman).
 - Keep the request bit helper local to stream.c.

v2:
 - Track outstanding requests by type instead of sequence (Xin Long).
 - Drop the redundant arithmetic guard (Xin Long).

v1: https://lore.kernel.org/netdev/20260730110225.37371-1-juny24602@gmail.com/

 include/net/sctp/structs.h |  2 +-
 net/sctp/stream.c          | 39 +++++++++++++++++++++++++++-----------
 2 files changed, 29 insertions(+), 12 deletions(-)

diff --git a/include/net/sctp/structs.h b/include/net/sctp/structs.h
index cccc662..b21f23b 100644
--- a/include/net/sctp/structs.h
+++ b/include/net/sctp/structs.h
@@ -2057,7 +2057,7 @@ struct sctp_association {
 	     force_delay:1;
 
 	__u8 strreset_enable;
-	__u8 strreset_outstanding; /* request param count on the fly */
+	__u8 strreset_outstanding; /* request param bitmask on the fly */
 
 	__u32 strreset_outseq; /* Update after receiving response */
 	__u32 strreset_inseq; /* Update after receiving request */
diff --git a/net/sctp/stream.c b/net/sctp/stream.c
index cfca5aa..e1a215d 100644
--- a/net/sctp/stream.c
+++ b/net/sctp/stream.c
@@ -22,6 +22,9 @@
 #include <net/sctp/sm.h>
 #include <net/sctp/stream_sched.h>
 
+#define SCTP_STRRESET_BIT(type) \
+	BIT(ntohs(type) - ntohs(SCTP_PARAM_RESET_OUT_REQUEST))
+
 static void sctp_stream_shrink_out(struct sctp_stream *stream, __u16 outcnt)
 {
 	struct sctp_association *asoc;
@@ -372,7 +375,9 @@ int sctp_send_reset_streams(struct sctp_association *asoc,
 		goto out;
 	}
 
-	asoc->strreset_outstanding = out + in;
+	asoc->strreset_outstanding =
+		(out ? SCTP_STRRESET_BIT(SCTP_PARAM_RESET_OUT_REQUEST) : 0) |
+		(in ? SCTP_STRRESET_BIT(SCTP_PARAM_RESET_IN_REQUEST) : 0);
 
 out:
 	return retval;
@@ -417,7 +422,8 @@ int sctp_send_reset_assoc(struct sctp_association *asoc)
 		return retval;
 	}
 
-	asoc->strreset_outstanding = 1;
+	asoc->strreset_outstanding =
+		SCTP_STRRESET_BIT(SCTP_PARAM_RESET_TSN_REQUEST);
 
 	return 0;
 }
@@ -474,7 +480,9 @@ int sctp_send_add_streams(struct sctp_association *asoc,
 		goto out;
 	}
 
-	asoc->strreset_outstanding = !!out + !!in;
+	asoc->strreset_outstanding =
+		(out ? SCTP_STRRESET_BIT(SCTP_PARAM_RESET_ADD_OUT_STREAMS) : 0) |
+		(in ? SCTP_STRRESET_BIT(SCTP_PARAM_RESET_ADD_IN_STREAMS) : 0);
 
 out:
 	return retval;
@@ -564,13 +572,16 @@ struct sctp_chunk *sctp_process_strreset_outreq(
 	if (asoc->strreset_chunk) {
 		if (!sctp_chunk_lookup_strreset_param(
 				asoc, outreq->response_seq,
-				SCTP_PARAM_RESET_IN_REQUEST, true)) {
+				SCTP_PARAM_RESET_IN_REQUEST, true) ||
+		    !(asoc->strreset_outstanding &
+		      SCTP_STRRESET_BIT(SCTP_PARAM_RESET_IN_REQUEST))) {
 			/* same process with outstanding isn't 0 */
 			result = SCTP_STRRESET_ERR_IN_PROGRESS;
 			goto out;
 		}
 
-		asoc->strreset_outstanding--;
+		asoc->strreset_outstanding &=
+			~SCTP_STRRESET_BIT(SCTP_PARAM_RESET_IN_REQUEST);
 		asoc->strreset_outseq++;
 
 		if (!asoc->strreset_outstanding) {
@@ -669,7 +680,8 @@ struct sctp_chunk *sctp_process_strreset_inreq(
 			SCTP_SO(stream, i)->state = SCTP_STREAM_CLOSED;
 
 	asoc->strreset_chunk = chunk;
-	asoc->strreset_outstanding = 1;
+	asoc->strreset_outstanding =
+		SCTP_STRRESET_BIT(SCTP_PARAM_RESET_OUT_REQUEST);
 	sctp_chunk_hold(asoc->strreset_chunk);
 
 	result = SCTP_STRRESET_PERFORMED;
@@ -816,13 +828,16 @@ struct sctp_chunk *sctp_process_strreset_addstrm_out(
 
 	if (asoc->strreset_chunk) {
 		if (!sctp_chunk_lookup_strreset_param(
-			asoc, 0, SCTP_PARAM_RESET_ADD_IN_STREAMS, false)) {
+			asoc, 0, SCTP_PARAM_RESET_ADD_IN_STREAMS, false) ||
+		    !(asoc->strreset_outstanding &
+		      SCTP_STRRESET_BIT(SCTP_PARAM_RESET_ADD_IN_STREAMS))) {
 			/* same process with outstanding isn't 0 */
 			result = SCTP_STRRESET_ERR_IN_PROGRESS;
 			goto out;
 		}
 
-		asoc->strreset_outstanding--;
+		asoc->strreset_outstanding &=
+			~SCTP_STRRESET_BIT(SCTP_PARAM_RESET_ADD_IN_STREAMS);
 		asoc->strreset_outseq++;
 
 		if (!asoc->strreset_outstanding) {
@@ -899,7 +914,8 @@ struct sctp_chunk *sctp_process_strreset_addstrm_in(
 		goto out;
 
 	asoc->strreset_chunk = chunk;
-	asoc->strreset_outstanding = 1;
+	asoc->strreset_outstanding =
+		SCTP_STRRESET_BIT(SCTP_PARAM_RESET_ADD_OUT_STREAMS);
 	sctp_chunk_hold(asoc->strreset_chunk);
 
 	stream->outcnt = outcnt;
@@ -929,7 +945,8 @@ struct sctp_chunk *sctp_process_strreset_resp(
 
 	req = sctp_chunk_lookup_strreset_param(asoc, resp->response_seq, 0,
 					       true);
-	if (!req)
+	if (!req || !(asoc->strreset_outstanding &
+		      SCTP_STRRESET_BIT(req->type)))
 		return NULL;
 
 	result = ntohl(resp->result);
@@ -1079,7 +1096,7 @@ struct sctp_chunk *sctp_process_strreset_resp(
 			nums, 0, GFP_ATOMIC);
 	}
 
-	asoc->strreset_outstanding--;
+	asoc->strreset_outstanding &= ~SCTP_STRRESET_BIT(req->type);
 	asoc->strreset_outseq++;
 
 	/* remove everything for this reconf request */
-- 
2.55.0