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Date: Fri, 07 Dec 2012 23:12:43 +0100 From: Johannes Berg <johannes@...solutions.net> To: David Miller <davem@...emloft.net> Cc: eric@...it.org, netdev@...r.kernel.org, linux-wireless@...r.kernel.org, linville@...driver.com, Eric Dumazet <eric.dumazet@...il.com> Subject: Re: [RFC PATCH] af_packet: don't to defrag shared skb On Fri, 2012-12-07 at 22:41 +0100, Johannes Berg wrote: > wpa_supplicant opens a packet socket for ETH_P_EAPOL, which indirectly > eventually calls dev_add_pack(). But if you do the same for another > socket, you'll get the same again, and then deliver_skb() will deliver > only a refcounted packet to the prot_hook->func(). > > This seems like it could very well cause the problem? Ok I couldn't reproduce it because suricata didn't work this way, but I did try using tcpdump (without the fanout) and deliver_skb() *is* called twice for each packet as I thought. It thus seems the problem is entirely in af_packet itself. It was changed a bit by Eric Dumazet in bc416d9768 but the original code goes back to the original defrag support in 7736d33f4, as far as I can tell. aec27311c changed the code to not do skb_clone(), but it seems the skb_share_check() should be before the pskb_pull(). Well, it seems ip_check_defrag() should simply not modify the SKB before it unshares it ... like this maybe: diff --git a/net/ipv4/ip_fragment.c b/net/ipv4/ip_fragment.c index 448e685..8d5cc75 100644 --- a/net/ipv4/ip_fragment.c +++ b/net/ipv4/ip_fragment.c @@ -707,28 +707,27 @@ EXPORT_SYMBOL(ip_defrag); struct sk_buff *ip_check_defrag(struct sk_buff *skb, u32 user) { - const struct iphdr *iph; + struct iphdr iph; u32 len; if (skb->protocol != htons(ETH_P_IP)) return skb; - if (!pskb_may_pull(skb, sizeof(struct iphdr))) + if (!skb_copy_bits(skb, 0, &iph, sizeof(iph))) return skb; - iph = ip_hdr(skb); - if (iph->ihl < 5 || iph->version != 4) + if (iph.ihl < 5 || iph.version != 4) return skb; - if (!pskb_may_pull(skb, iph->ihl*4)) - return skb; - iph = ip_hdr(skb); - len = ntohs(iph->tot_len); - if (skb->len < len || len < (iph->ihl * 4)) + + len = ntohs(iph.tot_len); + if (skb->len < len || len < (iph.ihl * 4)) return skb; - if (ip_is_fragment(ip_hdr(skb))) { + if (ip_is_fragment(&iph)) { skb = skb_share_check(skb, GFP_ATOMIC); if (skb) { + if (!pskb_may_pull(skb, iph.ihl*4)) + return skb; if (pskb_trim_rcsum(skb, len)) return skb; memset(IPCB(skb), 0, sizeof(struct inet_skb_parm)); johannes -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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