[PATCH 4.11 036/115] sctp: fix ICMP processing if skb is non-linear

Greg Kroah-Hartman
2017-06-05T16:30:00Z

From: Davide Caratti <dcaratti@redhat.com>

[ 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.

Signed-off-by: Davide Caratti <dcaratti@redhat.com>
Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Acked-by: Vlad Yasevich <vyasevich@gmail.com>
Reviewed-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/sctp/input.c | 16 +++++++++-------
1 file changed, 9 insertions(+), 7 deletions(-)

--- a/net/sctp/input.c
+++ b/net/sctp/input.c
@@ -473,15 +473,14 @@ 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;

@@ -516,13 +515,16 @@ 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;
}