[PATCH net v4 2/2] sctp: fix stream->outcnt underflow on duplicate RECONF responses

[Jun Yang <juny24602@gmail.com>]

From: Jun Yang <junvyyang@tencent.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>
---
v4:
 - Restore the SCTP_STRRESET_SET/CLEAR/TEST() helpers, each of which is
   used more than once, so open-coding them only adds lines.

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 cccc662561aa..b21f23b736fd 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 cfca5aa28c1a..9fee0da78845 100644
--- a/net/sctp/stream.c
+++ b/net/sctp/stream.c
@@ -22,6 +22,15 @@
 #include <net/sctp/sm.h>
 #include <net/sctp/stream_sched.h>
 
+#define SCTP_STRRESET_MASK(type) \
+	BIT(ntohs(type) - ntohs(SCTP_PARAM_RESET_OUT_REQUEST))
+#define SCTP_STRRESET_TEST(asoc, type) \
+	((asoc)->strreset_outstanding & SCTP_STRRESET_MASK(type))
+#define SCTP_STRRESET_SET(asoc, type) \
+	((asoc)->strreset_outstanding |= SCTP_STRRESET_MASK(type))
+#define SCTP_STRRESET_CLEAR(asoc, type) \
+	((asoc)->strreset_outstanding &= ~SCTP_STRRESET_MASK(type))
+
 static void sctp_stream_shrink_out(struct sctp_stream *stream, __u16 outcnt)
 {
 	struct sctp_association *asoc;
@@ -372,7 +381,10 @@ int sctp_send_reset_streams(struct sctp_association *asoc,
 		goto out;
 	}
 
-	asoc->strreset_outstanding = out + in;
+	if (out)
+		SCTP_STRRESET_SET(asoc, SCTP_PARAM_RESET_OUT_REQUEST);
+	if (in)
+		SCTP_STRRESET_SET(asoc, SCTP_PARAM_RESET_IN_REQUEST);
 
 out:
 	return retval;
@@ -417,7 +429,7 @@ int sctp_send_reset_assoc(struct sctp_association *asoc)
 		return retval;
 	}
 
-	asoc->strreset_outstanding = 1;
+	SCTP_STRRESET_SET(asoc, SCTP_PARAM_RESET_TSN_REQUEST);
 
 	return 0;
 }
@@ -474,7 +486,10 @@ int sctp_send_add_streams(struct sctp_association *asoc,
 		goto out;
 	}
 
-	asoc->strreset_outstanding = !!out + !!in;
+	if (out)
+		SCTP_STRRESET_SET(asoc, SCTP_PARAM_RESET_ADD_OUT_STREAMS);
+	if (in)
+		SCTP_STRRESET_SET(asoc, SCTP_PARAM_RESET_ADD_IN_STREAMS);
 
 out:
 	return retval;
@@ -564,13 +579,14 @@ 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) ||
+		    !SCTP_STRRESET_TEST(asoc, SCTP_PARAM_RESET_IN_REQUEST)) {
 			/* same process with outstanding isn't 0 */
 			result = SCTP_STRRESET_ERR_IN_PROGRESS;
 			goto out;
 		}
 
-		asoc->strreset_outstanding--;
+		SCTP_STRRESET_CLEAR(asoc, SCTP_PARAM_RESET_IN_REQUEST);
 		asoc->strreset_outseq++;
 
 		if (!asoc->strreset_outstanding) {
@@ -669,7 +685,7 @@ struct sctp_chunk *sctp_process_strreset_inreq(
 			SCTP_SO(stream, i)->state = SCTP_STREAM_CLOSED;
 
 	asoc->strreset_chunk = chunk;
-	asoc->strreset_outstanding = 1;
+	SCTP_STRRESET_SET(asoc, SCTP_PARAM_RESET_OUT_REQUEST);
 	sctp_chunk_hold(asoc->strreset_chunk);
 
 	result = SCTP_STRRESET_PERFORMED;
@@ -816,13 +832,14 @@ 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) ||
+		    !SCTP_STRRESET_TEST(asoc, SCTP_PARAM_RESET_ADD_IN_STREAMS)) {
 			/* same process with outstanding isn't 0 */
 			result = SCTP_STRRESET_ERR_IN_PROGRESS;
 			goto out;
 		}
 
-		asoc->strreset_outstanding--;
+		SCTP_STRRESET_CLEAR(asoc, SCTP_PARAM_RESET_ADD_IN_STREAMS);
 		asoc->strreset_outseq++;
 
 		if (!asoc->strreset_outstanding) {
@@ -899,7 +916,7 @@ struct sctp_chunk *sctp_process_strreset_addstrm_in(
 		goto out;
 
 	asoc->strreset_chunk = chunk;
-	asoc->strreset_outstanding = 1;
+	SCTP_STRRESET_SET(asoc, SCTP_PARAM_RESET_ADD_OUT_STREAMS);
 	sctp_chunk_hold(asoc->strreset_chunk);
 
 	stream->outcnt = outcnt;
@@ -929,7 +946,7 @@ struct sctp_chunk *sctp_process_strreset_resp(
 
 	req = sctp_chunk_lookup_strreset_param(asoc, resp->response_seq, 0,
 					       true);
-	if (!req)
+	if (!req || !SCTP_STRRESET_TEST(asoc, 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--;
+	SCTP_STRRESET_CLEAR(asoc, req->type);
 	asoc->strreset_outseq++;
 
 	/* remove everything for this reconf request */
-- 
2.55.0