sctp: auth: propagate HMAC calculation errors to callers

sctp_auth_calculate_hmac() can fail when building the association secret
under memory pressure, but its void return silently leaves the HMAC digest
zeroed.  On the receive path, sctp_sf_authenticate() compares this zeroed
digest against the peer-supplied one using crypto_memneq(), potentially
accepting an all-zero HMAC from the peer if the allocation failed.  On the
send path, sctp_packet_pack() transmits a packet with a zeroed HMAC that
the peer would reject.

Improve error handling by making sctp_auth_calculate_hmac() return int:
- sctp_sf_authenticate() returns SCTP_IERROR_NOMEM instead of accepting
  a zero HMAC.
- sctp_packet_pack() drops the packet on failure instead of transmitting
  a zeroed HMAC.

Update the declaration in auth.h accordingly.

Assisted-by: LLM
Signed-off-by: Qing Luo <luoqing@kylinos.cn>
Acked-by: Xin Long <lucien.xin@gmail.com>
Link: https://patch.msgid.link/20260807064314.500742-1-l1138897701@163.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

3 files changed, 21 insertions, 10 deletions

diff --git a/net/sctp/auth.c b/net/sctp/auth.c
index c901d373af80..6de66f56c41c 100644
--- a/net/sctp/auth.c
+++ b/net/sctp/auth.c
@@ -613,9 +613,9 @@ int sctp_auth_recv_cid(enum sctp_cid chunk, const struct sctp_association *asoc)
  *    zero (as shown in Figure 6) followed by all chunks that are placed
  *    after the AUTH chunk in the SCTP packet.
  */
-void sctp_auth_calculate_hmac(const struct sctp_association *asoc,
-			      struct sk_buff *skb, struct sctp_auth_chunk *auth,
-			      struct sctp_shared_key *ep_key, gfp_t gfp)
+int sctp_auth_calculate_hmac(const struct sctp_association *asoc,
+			     struct sk_buff *skb, struct sctp_auth_chunk *auth,
+			     struct sctp_shared_key *ep_key, gfp_t gfp)
 {
 	struct sctp_auth_bytes *asoc_key;
 	__u16 key_id, hmac_id;
@@ -636,7 +636,7 @@ void sctp_auth_calculate_hmac(const struct sctp_association *asoc,
 		/* ep_key can't be NULL here */
 		asoc_key = sctp_auth_asoc_create_secret(asoc, ep_key, gfp);
 		if (!asoc_key)
-			return;
+			return -ENOMEM;
 
 		free_key = 1;
 	}
@@ -654,6 +654,8 @@ void sctp_auth_calculate_hmac(const struct sctp_association *asoc,
 
 	if (free_key)
 		sctp_auth_key_put(asoc_key);
+
+	return 0;
 }
 
 /* API Helpers */
diff --git a/net/sctp/output.c b/net/sctp/output.c
index 23e96305cad7..3d7ead9d40e1 100644
--- a/net/sctp/output.c
+++ b/net/sctp/output.c
@@ -517,8 +517,14 @@ merge:
 		}
 
 		if (auth) {
-			sctp_auth_calculate_hmac(tp->asoc, nskb, auth,
-						 packet->auth->shkey, gfp);
+			if (sctp_auth_calculate_hmac(tp->asoc, nskb, auth,
+						     packet->auth->shkey, gfp)) {
+				sctp_chunk_free(packet->auth);
+				packet->auth = NULL;
+				if (gso)
+					kfree_skb(nskb);
+				return -ENOMEM;
+			}
 			/* free auth if no more chunks, or add it back */
 			if (list_empty(&packet->chunk_list))
 				sctp_chunk_free(packet->auth);
@@ -619,7 +625,7 @@ int sctp_packet_transmit(struct sctp_packet *packet, gfp_t gfp)
 
 	/* pack up chunks */
 	pkt_count = sctp_packet_pack(packet, head, gso, gfp);
-	if (!pkt_count) {
+	if (pkt_count <= 0) {
 		kfree_skb(head);
 		goto out;
 	}
diff --git a/net/sctp/sm_statefuns.c b/net/sctp/sm_statefuns.c
index 708fa07d5fff..bb89c9b52e0b 100644
--- a/net/sctp/sm_statefuns.c
+++ b/net/sctp/sm_statefuns.c
@@ -4455,9 +4455,12 @@ static enum sctp_ierror sctp_sf_authenticate(
 
 	memset(digest, 0, sig_len);
 
-	sctp_auth_calculate_hmac(asoc, chunk->skb,
-				 (struct sctp_auth_chunk *)chunk->chunk_hdr,
-				 sh_key, GFP_ATOMIC);
+	if (sctp_auth_calculate_hmac(asoc, chunk->skb,
+				     (struct sctp_auth_chunk *)chunk->chunk_hdr,
+				     sh_key, GFP_ATOMIC)) {
+		kfree(save_digest);
+		return SCTP_IERROR_NOMEM;
+	}
 
 	/* Discard the packet if the digests do not match */
 	if (crypto_memneq(save_digest, digest, sig_len)) {