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

[Herbert Xu]

Hi:

[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 <[EMAIL PROTECTED]>

Cheers,
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Email: Herbert Xu ~{PmV>HI~} <[EMAIL PROTECTED]>
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--
diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index fd99fbd..76ec973 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -462,6 +462,7 @@ 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) ||
@@ -485,7 +486,7 @@ 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;
                        }
                }
 
@@ -496,6 +497,7 @@ 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 6338a9c..bb9b183 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -609,6 +609,7 @@ 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) ||
@@ -631,7 +632,7 @@ 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;
                        }
                }
 
@@ -662,6 +663,7 @@ 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));
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