[INET]: Prevent out-of-sync truesize on ip_fragment slow path

When ip_fragment has to hit the slow path the value of skb->truesize
may go out of sync because we would have updated it without changing
the packet length.  This violates the constraints on truesize.

This patch postpones the update of skb->truesize to prevent this.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index 18070ca..6e4d5f4 100644 (file)
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -476,6 +476,7 @@ int ip_fragment(struct sk_buff *skb, int (*output)(struct sk_buff*))
        if (skb_shinfo(skb)->frag_list) {
                struct sk_buff *frag;
                int first_len = skb_pagelen(skb);
+               int truesizes = 0;
 
                if (first_len - hlen > mtu ||
                    ((first_len - hlen) & 7) ||
@@ -499,7 +500,7 @@ int ip_fragment(struct sk_buff *skb, int (*output)(struct sk_buff*))
                                sock_hold(skb->sk);
                                frag->sk = skb->sk;
                                frag->destructor = sock_wfree;
-                               skb->truesize -= frag->truesize;
+                               truesizes += frag->truesize;
                        }
                }
 
@@ -510,6 +511,7 @@ int ip_fragment(struct sk_buff *skb, int (*output)(struct sk_buff*))
                frag = skb_shinfo(skb)->frag_list;
                skb_shinfo(skb)->frag_list = NULL;
                skb->data_len = first_len - skb_headlen(skb);
+               skb->truesize -= truesizes;
                skb->len = first_len;
                iph->tot_len = htons(first_len);
                iph->frag_off = htons(IP_MF);

diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index 15c4f6c..cfe9e70 100644 (file)
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -636,6 +636,7 @@ static int ip6_fragment(struct sk_buff *skb, int (*output)(struct sk_buff *))
 
        if (skb_shinfo(skb)->frag_list) {
                int first_len = skb_pagelen(skb);
+               int truesizes = 0;
 
                if (first_len - hlen > mtu ||
                    ((first_len - hlen) & 7) ||
@@ -658,7 +659,7 @@ static int ip6_fragment(struct sk_buff *skb, int (*output)(struct sk_buff *))
                                sock_hold(skb->sk);
                                frag->sk = skb->sk;
                                frag->destructor = sock_wfree;
-                               skb->truesize -= frag->truesize;
+                               truesizes += frag->truesize;
                        }
                }
 
@@ -689,6 +690,7 @@ static int ip6_fragment(struct sk_buff *skb, int (*output)(struct sk_buff *))
 
                first_len = skb_pagelen(skb);
                skb->data_len = first_len - skb_headlen(skb);
+               skb->truesize -= truesizes;
                skb->len = first_len;
                ipv6_hdr(skb)->payload_len = htons(first_len -
                                                   sizeof(struct ipv6hdr));