On Fri, May 19, 2017 at 11:34 PM, Davide Caratti <dcaratti@xxxxxxxxxx> wrote:
> when the ICMP packet is carried by a paged skb, sctp_err_lookup() may fail
> validation even if the payload contents match an open socket: as a
> consequence, sometimes ICMPs are wrongly ignored. Use skb_header_pointer()
> to retrieve encapsulated SCTP headers, to ensure that ICMP payloads are
> validated correctly, also when skbs are non-linear.
>
> Signed-off-by: Davide Caratti <dcaratti@xxxxxxxxxx>
> ---
> include/net/sctp/sctp.h | 2 +-
> net/sctp/input.c | 29 +++++++++++++++++++----------
> net/sctp/ipv6.c | 2 +-
> 3 files changed, 21 insertions(+), 12 deletions(-)
>
> diff --git a/include/net/sctp/sctp.h b/include/net/sctp/sctp.h
> index 069582e..1b8c16b 100644
> --- a/include/net/sctp/sctp.h
> +++ b/include/net/sctp/sctp.h
> @@ -152,7 +152,7 @@ void sctp_v4_err(struct sk_buff *skb, u32 info);
> void sctp_hash_endpoint(struct sctp_endpoint *);
> void sctp_unhash_endpoint(struct sctp_endpoint *);
> struct sock *sctp_err_lookup(struct net *net, int family, struct sk_buff *,
> - struct sctphdr *, struct sctp_association **,
> + struct sctp_association **,
> struct sctp_transport **);
> void sctp_err_finish(struct sock *, struct sctp_transport *);
> void sctp_icmp_frag_needed(struct sock *, struct sctp_association *,
> diff --git a/net/sctp/input.c b/net/sctp/input.c
> index 0e06a27..7f3f983 100644
> --- a/net/sctp/input.c
> +++ b/net/sctp/input.c
> @@ -469,19 +469,19 @@ void sctp_icmp_proto_unreachable(struct sock *sk,
>
> /* Common lookup code for icmp/icmpv6 error handler. */
> struct sock *sctp_err_lookup(struct net *net, int family, struct sk_buff *skb,
> - struct sctphdr *sctphdr,
> struct sctp_association **app,
> struct sctp_transport **tpp)
> {
> + struct sctp_init_chunk _chunkhdr, *chunkhdr;
> + struct sctphdr _sctphdr, *sctphdr;
> 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);
> + int offset;
> + __u32 vtag;
>
> *app = NULL; *tpp = NULL;
>
> @@ -515,14 +515,23 @@ struct sock *sctp_err_lookup(struct net *net, int family, struct sk_buff *skb,
> * or the chunk type or the Initiate Tag does not match, silently
> * discard the packet.
> */
> + offset = skb_transport_offset(skb);
> + sctphdr = skb_header_pointer(skb, offset, sizeof(_sctphdr), &_sctphdr);
> + if (unlikely(!sctphdr))
> + goto out;
> +
> + vtag = ntohl(sctphdr->vtag);
> if (vtag == 0) {
> - chunkhdr = (void *)sctphdr + sizeof(struct sctphdr);
> - if (len < sizeof(struct sctphdr) + sizeof(sctp_chunkhdr_t)
> - + sizeof(__be32) ||
> + offset += sizeof(_sctphdr);
will be nice to delete this line, and use
> + /* chunk header + first 4 octects of init header */
> + chunkhdr = skb_header_pointer(skb, offset,
chunkhdr = skb_header_pointer(skb, offset + sizeof(_sctphdr), ;)
wdyt?
> + 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;
> }
> @@ -585,7 +594,7 @@ void sctp_v4_err(struct sk_buff *skb, __u32 info)
> savesctp = skb->transport_header;
> skb_reset_network_header(skb);
> skb_set_transport_header(skb, ihlen);
> - sk = sctp_err_lookup(net, AF_INET, skb, sctp_hdr(skb), &asoc, &transport);
> + sk = sctp_err_lookup(net, AF_INET, skb, &asoc, &transport);
> /* Put back, the original values. */
> skb->network_header = saveip;
> skb->transport_header = savesctp;
> diff --git a/net/sctp/ipv6.c b/net/sctp/ipv6.c
> index 142b70e..d72c8d5 100644
> --- a/net/sctp/ipv6.c
> +++ b/net/sctp/ipv6.c
> @@ -157,7 +157,7 @@ static void sctp_v6_err(struct sk_buff *skb, struct inet6_skb_parm *opt,
> savesctp = skb->transport_header;
> skb_reset_network_header(skb);
> skb_set_transport_header(skb, offset);
> - sk = sctp_err_lookup(net, AF_INET6, skb, sctp_hdr(skb), &asoc, &transport);
> + sk = sctp_err_lookup(net, AF_INET6, skb, &asoc, &transport);
> /* Put back, the original pointers. */
> skb->network_header = saveip;
> skb->transport_header = savesctp;
> --
> 2.7.4
>
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