[DCCP]: Fix skb->cb conflicts with IP

dev_queue_xmit() and the other IP output functions expect to get a skb with clear or properly initialized skb->cb. Unlike TCP and UDP, the dccp_skb_cb doesn't contain a struct inet_skb_parm at the beginning, so the DCCP-specific data is interpreted by the IP output functions. This can cause false negatives for the conditional POST_ROUTING hook invocation, making the packet bypass the hook. Add a inet_skb_parm/inet6_skb_parm union to the beginning of dccp_skb_cb to avoid clashes. Also add a BUILD_BUG_ON to make sure it fits in the cb. [ Combined with patch from Gerrit Renker to remove two now unnecessary memsets of IPCB(skb)->opt ] Signed-off-by: Patrick McHardy <[email protected]> Acked-by: Arnaldo Carvalho de Melo <[email protected]> Signed-off-by: David S. Miller <[email protected]>
iegor · Apr 13, 2008 · 028b027 · 028b027
1 parent ae1b6a3
commit 028b027
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Showing 4 changed files with 9 additions and 2 deletions.
diff --git a/net/dccp/dccp.h b/net/dccp/dccp.h
@@ -325,6 +325,12 @@ static inline int dccp_bad_service_code(const struct sock *sk,
  * This is used for transmission as well as for reception.
  */
 struct dccp_skb_cb {
+	union {
+		struct inet_skb_parm	h4;
+#if defined(CONFIG_IPV6) || defined (CONFIG_IPV6_MODULE)
+		struct inet6_skb_parm	h6;
+#endif
+	} header;
 	__u8  dccpd_type:4;
 	__u8  dccpd_ccval:4;
 	__u8  dccpd_reset_code,

diff --git a/net/dccp/ipv4.c b/net/dccp/ipv4.c
@@ -489,7 +489,6 @@ static int dccp_v4_send_response(struct sock *sk, struct request_sock *req,
 
 		dh->dccph_checksum = dccp_v4_csum_finish(skb, ireq->loc_addr,
 							      ireq->rmt_addr);
-		memset(&(IPCB(skb)->opt), 0, sizeof(IPCB(skb)->opt));
 		err = ip_build_and_send_pkt(skb, sk, ireq->loc_addr,
 					    ireq->rmt_addr,
 					    ireq->opt);

diff --git a/net/dccp/output.c b/net/dccp/output.c
@@ -126,7 +126,6 @@ static int dccp_transmit_skb(struct sock *sk, struct sk_buff *skb)
 
 		DCCP_INC_STATS(DCCP_MIB_OUTSEGS);
 
-		memset(&(IPCB(skb)->opt), 0, sizeof(IPCB(skb)->opt));
 		err = icsk->icsk_af_ops->queue_xmit(skb, 0);
 		return net_xmit_eval(err);
 	}

diff --git a/net/dccp/proto.c b/net/dccp/proto.c
@@ -1057,6 +1057,9 @@ static int __init dccp_init(void)
 	int ehash_order, bhash_order, i;
 	int rc = -ENOBUFS;
 
+	BUILD_BUG_ON(sizeof(struct dccp_skb_cb) >
+		     FIELD_SIZEOF(struct sk_buff, cb));
+
 	dccp_hashinfo.bind_bucket_cachep =
 		kmem_cache_create("dccp_bind_bucket",
 				  sizeof(struct inet_bind_bucket), 0,