ipv4: ip_do_fragment: fix headroom tests

Some time ago David Woodhouse reported skb_under_panic
when we try to push ethernet header to fragmented ipv6 skbs.
It was fixed for ipv6 by Florian Westphal in
commit 1d325d217c7f ("ipv6: ip6_fragment: fix headroom tests and skb leak")

However similar problem still exist in ipv4.

It does not trigger skb_under_panic due paranoid check
in ip_finish_output2, however according to Alexey Kuznetsov
current state is abnormal and ip_fragment should be fixed too.

Signed-off-by: Vasily Averin <vvs@virtuozzo.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index 7eb252d..50c74cd 100644 (file)
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -599,6 +599,7 @@ int ip_do_fragment(struct net *net, struct sock *sk, struct sk_buff *skb,
        hlen = iph->ihl * 4;
        mtu = mtu - hlen;       /* Size of data space */
        IPCB(skb)->flags |= IPSKB_FRAG_COMPLETE;
+       ll_rs = LL_RESERVED_SPACE(rt->dst.dev);
 
        /* When frag_list is given, use it. First, check its validity:
         * some transformers could create wrong frag_list or break existing
@@ -614,14 +615,15 @@ int ip_do_fragment(struct net *net, struct sock *sk, struct sk_buff *skb,
                if (first_len - hlen > mtu ||
                    ((first_len - hlen) & 7) ||
                    ip_is_fragment(iph) ||
-                   skb_cloned(skb))
+                   skb_cloned(skb) ||
+                   skb_headroom(skb) < ll_rs)
                        goto slow_path;
 
                skb_walk_frags(skb, frag) {
                        /* Correct geometry. */
                        if (frag->len > mtu ||
                            ((frag->len & 7) && frag->next) ||
-                           skb_headroom(frag) < hlen)
+                           skb_headroom(frag) < hlen + ll_rs)
                                goto slow_path_clean;
 
                        /* Partially cloned skb? */
@@ -711,8 +713,6 @@ slow_path:
        left = skb->len - hlen;         /* Space per frame */
        ptr = hlen;             /* Where to start from */
 
-       ll_rs = LL_RESERVED_SPACE(rt->dst.dev);
-
        /*
         *      Fragment the datagram.
         */