[PATCH net v2] sctp: validate stream count in sctp_process_strreset_inreq()

["Cen Zhang (Microsoft)" <blbllhy@gmail.com>]

When processing a RESET_IN_REQUEST from a peer,
sctp_process_strreset_inreq() derives the stream count from the
parameter length but does not check whether the resulting
RESET_OUT_REQUEST would exceed SCTP_MAX_CHUNK_LEN.

The OUT request header (sctp_strreset_outreq, 16 bytes) is 8 bytes
larger than the IN request header (sctp_strreset_inreq, 8 bytes).
Generally, the IP payload is bounded to 65535 bytes, so the stream
list cannot be large enough to trigger the overflow. However, on
interfaces with MTU > 65535 (e.g., loopback with IPv6 jumbograms), a
stream list that fits within the incoming IN parameter can cause a
__u16 overflow in sctp_make_strreset_req() when computing the OUT
request size, leading to an undersized skb allocation and a kernel
BUG:

  net/core/skbuff.c:207         skb_panic
  net/core/skbuff.c:2625        skb_put
  net/sctp/sm_make_chunk.c:1535 sctp_addto_chunk
  net/sctp/sm_make_chunk.c:3695 sctp_make_strreset_req
  net/sctp/stream.c:655         sctp_process_strreset_inreq

The local setsockopt path validates the generated reset request size.
However, for an incoming-only reset, it accounts for the smaller IN
request even though the peer must generate an OUT request with the same
stream list. Such a request cannot be completed successfully by the
peer.

Reject peer IN requests whose corresponding OUT request would exceed
SCTP_MAX_CHUNK_LEN. Also tighten the local check so it does not send an
IN request that would require an oversized OUT request from the peer.

Fixes: 7f9d68ac944e ("sctp: implement sender-side procedures for SSN Reset Request Parameter")
Reported-by: AutonomousCodeSecurity@microsoft.com
Closes: https://lore.kernel.org/all/20260707203215.2752-1-blbllhy@gmail.com/
Suggested-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: Cen Zhang (Microsoft) <blbllhy@gmail.com>
---
v2: Add the OUT request length check to the send path, as suggested by Xin Long.

 net/sctp/stream.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/net/sctp/stream.c b/net/sctp/stream.c
index 5c2fdedea088..34ffe6c945a4 100644
--- a/net/sctp/stream.c
+++ b/net/sctp/stream.c
@@ -308,7 +308,8 @@ int sctp_send_reset_streams(struct sctp_association *asoc,
 					goto out;
 
 			param_len += str_nums * sizeof(__u16) +
-				     sizeof(struct sctp_strreset_inreq);
+				     (out ? sizeof(struct sctp_strreset_inreq)
+					  : sizeof(struct sctp_strreset_outreq));
 		}
 
 		if (param_len > SCTP_MAX_CHUNK_LEN -
@@ -639,6 +640,9 @@ struct sctp_chunk *sctp_process_strreset_inreq(
 
 	nums = (ntohs(param.p->length) - sizeof(*inreq)) / sizeof(__u16);
 	str_p = inreq->list_of_streams;
+	if (nums * sizeof(__u16) + sizeof(struct sctp_strreset_outreq) >
+	    SCTP_MAX_CHUNK_LEN - sizeof(struct sctp_reconf_chunk))
+		goto out;
 	for (i = 0; i < nums; i++) {
 		if (ntohs(str_p[i]) >= stream->outcnt) {
 			result = SCTP_STRRESET_ERR_WRONG_SSN;
-- 
2.53.0