1. 28 Nov, 2013 2 commits
    • Eric Dumazet's avatar
      tcp: do not forget FIN in tcp_shifted_skb() · 7e369408
      Eric Dumazet authored
      [ Upstream commit 5e8a402f ]
      
      Yuchung found following problem :
      
       There are bugs in the SACK processing code, merging part in
       tcp_shift_skb_data(), that incorrectly resets or ignores the sacked
       skbs FIN flag. When a receiver first SACK the FIN sequence, and later
       throw away ofo queue (e.g., sack-reneging), the sender will stop
       retransmitting the FIN flag, and hangs forever.
      
      Following packetdrill test can be used to reproduce the bug.
      
      $ cat sack-merge-bug.pkt
      `sysctl -q net.ipv4.tcp_fack=0`
      
      // Establish a connection and send 10 MSS.
      0.000 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
      +.000 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
      +.000 bind(3, ..., ...) = 0
      +.000 listen(3, 1) = 0
      
      +.050 < S 0:0(0) win 32792 <mss 1000,sackOK,nop,nop,nop,wscale 7>
      +.000 > S. 0:0(0) ack 1 <mss 1460,nop,nop,sackOK,nop,wscale 6>
      +.001 < . 1:1(0) ack 1 win 1024
      +.000 accept(3, ..., ...) = 4
      
      +.100 write(4, ..., 12000) = 12000
      +.000 shutdown(4, SHUT_WR) = 0
      +.000 > . 1:10001(10000) ack 1
      +.050 < . 1:1(0) ack 2001 win 257
      +.000 > FP. 10001:12001(2000) ack 1
      +.050 < . 1:1(0) ack 2001 win 257 <sack 10001:11001,nop,nop>
      +.050 < . 1:1(0) ack 2001 win 257 <sack 10001:12002,nop,nop>
      // SACK reneg
      +.050 < . 1:1(0) ack 12001 win 257
      +0 %{ print "unacked: ",tcpi_unacked }%
      +5 %{ print "" }%
      
      First, a typo inverted left/right of one OR operation, then
      code forgot to advance end_seq if the merged skb carried FIN.
      
      Bug was added in 2.6.29 by commit 832d11c5
      ("tcp: Try to restore large SKBs while SACK processing")
      Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
      Signed-off-by: default avatarYuchung Cheng <ycheng@google.com>
      Acked-by: default avatarNeal Cardwell <ncardwell@google.com>
      Cc: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
      Acked-by: default avatarIlpo Järvinen <ilpo.jarvinen@helsinki.fi>
      Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
      Signed-off-by: default avatarBen Hutchings <ben@decadent.org.uk>
      7e369408
    • Eric Dumazet's avatar
      tcp: must unclone packets before mangling them · e5704e27
      Eric Dumazet authored
      [ Upstream commit c52e2421 ]
      
      TCP stack should make sure it owns skbs before mangling them.
      
      We had various crashes using bnx2x, and it turned out gso_size
      was cleared right before bnx2x driver was populating TC descriptor
      of the _previous_ packet send. TCP stack can sometime retransmit
      packets that are still in Qdisc.
      
      Of course we could make bnx2x driver more robust (using
      ACCESS_ONCE(shinfo->gso_size) for example), but the bug is TCP stack.
      
      We have identified two points where skb_unclone() was needed.
      
      This patch adds a WARN_ON_ONCE() to warn us if we missed another
      fix of this kind.
      
      Kudos to Neal for finding the root cause of this bug. Its visible
      using small MSS.
      Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
      Signed-off-by: default avatarNeal Cardwell <ncardwell@google.com>
      Cc: Yuchung Cheng <ycheng@google.com>
      Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
      Signed-off-by: default avatarBen Hutchings <ben@decadent.org.uk>
      e5704e27
  2. 26 Oct, 2013 38 commits