netfilter: nf_conntrack_dccp: fix skb_header_pointer API usages

Some occurences in the netfilter tree use skb_header_pointer() in
the following way ...

  struct dccp_hdr _dh, *dh;
  ...
  skb_header_pointer(skb, dataoff, sizeof(_dh), &dh);

... where dh itself is a pointer that is being passed as the copy
buffer. Instead, we need to use &_dh as the forth argument so that
we're copying the data into an actual buffer that sits on the stack.

Currently, we probably could overwrite memory on the stack (e.g.
with a possibly mal-formed DCCP packet), but unintentionally, as
we only want the buffer to be placed into _dh variable.

Fixes: 2bc780499aa3 ("[NETFILTER]: nf_conntrack: add DCCP protocol support")
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

diff --git a/net/netfilter/nf_conntrack_proto_dccp.c b/net/netfilter/nf_conntrack_proto_dccp.c
index 38412684a8824463e99f9fc46111a7874013c1bb..cb372f96f10dc3c2f60064e49b86d35c76c6cd1b 100644 (file)
--- a/net/netfilter/nf_conntrack_proto_dccp.c
+++ b/net/netfilter/nf_conntrack_proto_dccp.c
@@ -428,7 +428,7 @@ static bool dccp_new(struct nf_conn *ct, const struct sk_buff *skb,
        const char *msg;
        u_int8_t state;
 
-       dh = skb_header_pointer(skb, dataoff, sizeof(_dh), &dh);
+       dh = skb_header_pointer(skb, dataoff, sizeof(_dh), &_dh);
        BUG_ON(dh == NULL);
 
        state = dccp_state_table[CT_DCCP_ROLE_CLIENT][dh->dccph_type][CT_DCCP_NONE];
@@ -486,7 +486,7 @@ static int dccp_packet(struct nf_conn *ct, const struct sk_buff *skb,
        u_int8_t type, old_state, new_state;
        enum ct_dccp_roles role;
 
-       dh = skb_header_pointer(skb, dataoff, sizeof(_dh), &dh);
+       dh = skb_header_pointer(skb, dataoff, sizeof(_dh), &_dh);
        BUG_ON(dh == NULL);
        type = dh->dccph_type;
 
@@ -577,7 +577,7 @@ static int dccp_error(struct net *net, struct nf_conn *tmpl,
        unsigned int cscov;
        const char *msg;
 
-       dh = skb_header_pointer(skb, dataoff, sizeof(_dh), &dh);
+       dh = skb_header_pointer(skb, dataoff, sizeof(_dh), &_dh);
        if (dh == NULL) {
                msg = "nf_ct_dccp: short packet ";
                goto out_invalid;