ipv4: fix path MTU discovery with connection tracking
IPv4 conntrack defragments incoming packet at the PRE_ROUTING hook and (in case of forwarded packets) refragments them at POST_ROUTING independent of the IP_DF flag. Refragmentation uses the dst_mtu() of the local route without caring about the original fragment sizes, thereby breaking PMTUD. This patch fixes this by keeping track of the largest received fragment with IP_DF set and generates an ICMP fragmentation required error during refragmentation if that size exceeds the MTU. Signed-off-by: NPatrick McHardy <kaber@trash.net> Acked-by: NEric Dumazet <edumazet@google.com> Acked-by: NDavid S. Miller <davem@davemloft.net>
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