[NETFILTER]: nf_conntrack_ipv6: fix crash when handling fragments

When IPv6 connection tracking splits up a defragmented packet into
its original fragments, the packets are taken from a list and are
passed to the network stack with skb->next still set. This causes
dev_hard_start_xmit to treat them as GSO fragments, resulting in
a use after free when connection tracking handles the next fragment.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv6/netfilter/nf_conntrack_reasm.c b/net/ipv6/netfilter/nf_conntrack_reasm.c
index 37e5fca923aa14ec0322f543466a8d09e6d7fbab..d9c15402ba6619023b6f28633e14666ee615b09f 100644 (file)
--- a/net/ipv6/netfilter/nf_conntrack_reasm.c
+++ b/net/ipv6/netfilter/nf_conntrack_reasm.c
@@ -835,6 +835,8 @@ void nf_ct_frag6_output(unsigned int hooknum, struct sk_buff *skb,
                s->nfct_reasm = skb;
 
                s2 = s->next;
+               s->next = NULL;
+
                NF_HOOK_THRESH(PF_INET6, hooknum, s, in, out, okfn,
                               NF_IP6_PRI_CONNTRACK_DEFRAG + 1);
                s = s2;