From 88ac49fa287e2e0d3d3bc805dea1fec301aad1df Mon Sep 17 00:00:00 2001 From: Vicente Jimenez Aguilar Date: Mon, 31 Oct 2016 13:10:29 +0100 Subject: [PATCH] ipv4: icmp: Fix pMTU handling for rarest case Restore network resistance to weird ICMP fragmentation needed messages with next hop MTU equal to (or exceeding) dropped packet size Fixes: 46517008e116 ("ipv4: Kill ip_rt_frag_needed().") Signed-off-by: Vicente Jimenez Aguilar --- net/ipv4/icmp.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/net/ipv4/icmp.c b/net/ipv4/icmp.c index 38abe70..4c90d76 100644 --- a/net/ipv4/icmp.c +++ b/net/ipv4/icmp.c @@ -773,6 +773,7 @@ static bool icmp_tag_validation(int proto) static bool icmp_unreach(struct sk_buff *skb) { const struct iphdr *iph; + unsigned short old_mtu; struct icmphdr *icmph; struct net *net; u32 info = 0; @@ -819,6 +820,12 @@ static bool icmp_unreach(struct sk_buff *skb) /* fall through */ case 0: info = ntohs(icmph->un.frag.mtu); + /* Handle weird case where next hop MTU is + * equal to or exceeding dropped packet size + */ + old_mtu = ntohs(iph->tot_len); + if (info >= old_mtu) + info = old_mtu - 2; } break; case ICMP_SR_FAILED: -- 2.7.3