Patch "sctp: fix ICMP processing if skb is non-linear" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

sctp: fix ICMP processing if skb is non-linear

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
sctp-fix-icmp-processing-if-skb-is-non-linear.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Davide Caratti <[email protected]>
Date: Thu, 25 May 2017 19:14:56 +0200
Subject: sctp: fix ICMP processing if skb is non-linear

From: Davide Caratti <[email protected]>

[ Upstream commit 804ec7ebe8ea003999ca8d1bfc499edc6a9e07df ]

sometimes ICMP replies to INIT chunks are ignored by the client, even if the encapsulated SCTP headers match an open socket. This happens when the ICMP packet is carried by a paged skb: use skb_header_pointer() to read packet contents beyond the SCTP header, so that chunk header and initiate tag are validated correctly.

v2:
- don't use skb_header_pointer() to read the transport header, since icmp_socket_deliver() already puts these 8 bytes in the linear area.
- change commit message to make specific reference to INIT chunks.

---
 net/sctp/input.c |   16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

@@ -472,15 +472,14 @@ struct sock *sctp_err_lookup(struct net
 			     struct sctp_association **app,
 			     struct sctp_transport **tpp)
 {
+	struct sctp_init_chunk *chunkhdr, _chunkhdr;
 	union sctp_addr saddr;
 	union sctp_addr daddr;
 	struct sctp_af *af;
 	struct sock *sk = NULL;
 	struct sctp_association *asoc;
 	struct sctp_transport *transport = NULL;
-	struct sctp_init_chunk *chunkhdr;
 	__u32 vtag = ntohl(sctphdr->vtag);
-	int len = skb->len - ((void *)sctphdr - (void *)skb->data);
 
 	*app = NULL; *tpp = NULL;
 

@@ -515,13 +514,16 @@ struct sock *sctp_err_lookup(struct net
 	 * discard the packet.
 	 */
 	if (vtag == 0) {
-		chunkhdr = (void *)sctphdr + sizeof(struct sctphdr);
-		if (len < sizeof(struct sctphdr) + sizeof(sctp_chunkhdr_t)
-			  + sizeof(__be32) ||
+		/* chunk header + first 4 octects of init header */
+		chunkhdr = skb_header_pointer(skb, skb_transport_offset(skb) +
+					      sizeof(struct sctphdr),
+					      sizeof(struct sctp_chunkhdr) +
+					      sizeof(__be32), &_chunkhdr);
+		if (!chunkhdr ||
 		    chunkhdr->chunk_hdr.type != SCTP_CID_INIT ||
-		    ntohl(chunkhdr->init_hdr.init_tag) != asoc->c.my_vtag) {
+		    ntohl(chunkhdr->init_hdr.init_tag) != asoc->c.my_vtag)
 			goto out;
-		}
+
 	} else if (vtag != asoc->c.peer_vtag) {
 		goto out;
 	}

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/sctp-fix-icmp-processing-if-skb-is-non-linear.patch