[PATCH net-next] sctp: auth: propagate HMAC calculation errors to callers

[luoqing]

From: Qing Luo <luoqing@xxxxxxxxxx>

sctp_auth_calculate_hmac() silently returns when
sctp_auth_asoc_create_secret() fails under memory pressure,
leaving the digest zeroed. Callers then compare the zeroed
digest against the saved one, getting SCTP_IERROR_BAD_SIG
instead of the correct SCTP_IERROR_NOMEM.

Change sctp_auth_calculate_hmac() to return int so callers
can distinguish allocation failures from bad signatures:

- sctp_sf_authenticate() frees save_digest and returns
  SCTP_IERROR_NOMEM on failure.
- sctp_packet_pack() frees the auth chunk and returns 0
  (drop the packet). In the non-GSO path nskb equals head,
  so only free nskb in the GSO path to avoid a double-free;
  the caller handles head cleanup when pkt_count is 0.

Also update the declaration in auth.h to match.

Assisted-by: LLM # review
Signed-off-by: Qing Luo <luoqing@xxxxxxxxxx>
---
 include/net/sctp/auth.h |  6 +++---
 net/sctp/auth.c         |  6 ++++--
 net/sctp/output.c       | 10 ++++++++--
 net/sctp/sm_statefuns.c |  9 ++++++---
 4 files changed, 21 insertions(+), 10 deletions(-)

diff --git a/include/net/sctp/auth.h b/include/net/sctp/auth.h
index 6f2cd562b1de..eeb3297fe97d 100644
--- a/include/net/sctp/auth.h
+++ b/include/net/sctp/auth.h
@@ -83,9 +83,9 @@ int sctp_auth_send_cid(enum sctp_cid chunk,
 		       const struct sctp_association *asoc);
 int sctp_auth_recv_cid(enum sctp_cid chunk,
 		       const struct sctp_association *asoc);
-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);
 void sctp_auth_shkey_release(struct sctp_shared_key *sh_key);
 void sctp_auth_shkey_hold(struct sctp_shared_key *sh_key);
 
diff --git a/net/sctp/auth.c b/net/sctp/auth.c
index c901d373af80..4db3a3a4a457 100644
--- a/net/sctp/auth.c
+++ b/net/sctp/auth.c
@@ -613,7 +613,7 @@ 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,
+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)
 {
@@ -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..a7930cd9400e 100644
--- a/net/sctp/output.c
+++ b/net/sctp/output.c
@@ -517,8 +517,14 @@ static int sctp_packet_pack(struct sctp_packet *packet,
 		}
 
 		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 0;
+			}
 			/* free auth if no more chunks, or add it back */
 			if (list_empty(&packet->chunk_list))
 				sctp_chunk_free(packet->auth);
diff --git a/net/sctp/sm_statefuns.c b/net/sctp/sm_statefuns.c
index b01db33bbc36..b68de2c4dc26 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)) {
-- 
2.25.1