Subject: for 3.0 : please add "c16a98e ipv6: tcp: fix panic in SYN processing"

From: Willy Tarreau <[email-masked]>
Date: Fri, 18 Oct 2013 16:04:42 +0200

Greg, David,

one of our customers faced a panic in latest 2.6.32 when both somaxconn
and the listen backlog are large on an IPv6 socket. It was also reported
by one haproxy user on the latest RHEL6 kernel a few months ago. We found
that the same bug affects 3.0 up to and including 3.0.100.

Eric had already spotted that bug and fixed it in 3.2 with the following
patch :

  commit c16a98ed91597b40b22b540c6517103497ef8e74
  Author: Eric Dumazet <[email-masked]>
  Date:   Wed Nov 23 15:49:31 2011 -0500

    ipv6: tcp: fix panic in SYN processing
    
    commit 72a3effaf633bc ([NET]: Size listen hash tables using backlog
    hint) added a bug allowing inet6_synq_hash() to return an out of bound
    array index, because of u16 overflow.
    
    Bug can happen if system admins set net.core.somaxconn &
    net.ipv4.tcp_max_syn_backlog sysctls to values greater than 65536
    
    Signed-off-by: Eric Dumazet <[email-masked]>
    Signed-off-by: David S. Miller <[email-masked]>

In practice, the bug extends to lower values as well (32768 and above),
because reqsk_queue_alloc() can round the number of entries to double of
the backlog by doing roundup_pow_of_two(backlog+1), resulting in
inet6_csk_search_req() calling inet6_synq_hash() with too large an integer.

Could we please apply it to 3.0 before it finishes its life ?

Thanks,
Willy