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686dc2db2a
Fix a bug reported and analyzed by Nagaraj Arankal, where the handling
of a spurious non-SACK RTO could cause a connection to fail to clear
retrans_stamp, causing a later RTO to very prematurely time out the
connection with ETIMEDOUT.
Here is the buggy scenario, expanding upon Nagaraj Arankal's excellent
report:
(*1) Send one data packet on a non-SACK connection
(*2) Because no ACK packet is received, the packet is retransmitted
and we enter CA_Loss; but this retransmission is spurious.
(*3) The ACK for the original data is received. The transmitted packet
is acknowledged. The TCP timestamp is before the retrans_stamp,
so tcp_may_undo() returns true, and tcp_try_undo_loss() returns
true without changing state to Open (because tcp_is_sack() is
false), and tcp_process_loss() returns without calling
tcp_try_undo_recovery(). Normally after undoing a CA_Loss
episode, tcp_fastretrans_alert() would see that the connection
has returned to CA_Open and fall through and call
tcp_try_to_open(), which would set retrans_stamp to 0. However,
for non-SACK connections we hold the connection in CA_Loss, so do
not fall through to call tcp_try_to_open() and do not set
retrans_stamp to 0. So retrans_stamp is (erroneously) still
non-zero.
At this point the first "retransmission event" has passed and
been recovered from. Any future retransmission is a completely
new "event". However, retrans_stamp is erroneously still
set. (And we are still in CA_Loss, which is correct.)
(*4) After 16 minutes (to correspond with tcp_retries2=15), a new data
packet is sent. Note: No data is transmitted between (*3) and
(*4) and we disabled keep alives.
The socket's timeout SHOULD be calculated from this point in
time, but instead it's calculated from the prior "event" 16
minutes ago (step (*2)).
(*5) Because no ACK packet is received, the packet is retransmitted.
(*6) At the time of the 2nd retransmission, the socket returns
ETIMEDOUT, prematurely, because retrans_stamp is (erroneously)
too far in the past (set at the time of (*2)).
This commit fixes this bug by ensuring that we reuse in
tcp_try_undo_loss() the same careful logic for non-SACK connections
that we have in tcp_try_undo_recovery(). To avoid duplicating logic,
we factor out that logic into a new
tcp_is_non_sack_preventing_reopen() helper and call that helper from
both undo functions.
Fixes:
|
||
|---|---|---|
| .. | ||
| bpfilter | ||
| netfilter | ||
| af_inet.c | ||
| ah4.c | ||
| arp.c | ||
| bpf_tcp_ca.c | ||
| cipso_ipv4.c | ||
| datagram.c | ||
| devinet.c | ||
| esp4_offload.c | ||
| esp4.c | ||
| fib_frontend.c | ||
| fib_lookup.h | ||
| fib_notifier.c | ||
| fib_rules.c | ||
| fib_semantics.c | ||
| fib_trie.c | ||
| fou.c | ||
| gre_demux.c | ||
| gre_offload.c | ||
| icmp.c | ||
| igmp.c | ||
| inet_connection_sock.c | ||
| inet_diag.c | ||
| inet_fragment.c | ||
| inet_hashtables.c | ||
| inet_timewait_sock.c | ||
| inetpeer.c | ||
| ip_forward.c | ||
| ip_fragment.c | ||
| ip_gre.c | ||
| ip_input.c | ||
| ip_options.c | ||
| ip_output.c | ||
| ip_sockglue.c | ||
| ip_tunnel_core.c | ||
| ip_tunnel.c | ||
| ip_vti.c | ||
| ipcomp.c | ||
| ipconfig.c | ||
| ipip.c | ||
| ipmr_base.c | ||
| ipmr.c | ||
| Kconfig | ||
| Makefile | ||
| metrics.c | ||
| netfilter.c | ||
| netlink.c | ||
| nexthop.c | ||
| ping.c | ||
| proc.c | ||
| protocol.c | ||
| raw_diag.c | ||
| raw.c | ||
| route.c | ||
| syncookies.c | ||
| sysctl_net_ipv4.c | ||
| tcp_bbr.c | ||
| tcp_bic.c | ||
| tcp_bpf.c | ||
| tcp_cdg.c | ||
| tcp_cong.c | ||
| tcp_cubic.c | ||
| tcp_dctcp.c | ||
| tcp_dctcp.h | ||
| tcp_diag.c | ||
| tcp_fastopen.c | ||
| tcp_highspeed.c | ||
| tcp_htcp.c | ||
| tcp_hybla.c | ||
| tcp_illinois.c | ||
| tcp_input.c | ||
| tcp_ipv4.c | ||
| tcp_lp.c | ||
| tcp_metrics.c | ||
| tcp_minisocks.c | ||
| tcp_nv.c | ||
| tcp_offload.c | ||
| tcp_output.c | ||
| tcp_rate.c | ||
| tcp_recovery.c | ||
| tcp_scalable.c | ||
| tcp_timer.c | ||
| tcp_ulp.c | ||
| tcp_vegas.c | ||
| tcp_vegas.h | ||
| tcp_veno.c | ||
| tcp_westwood.c | ||
| tcp_yeah.c | ||
| tcp.c | ||
| tunnel4.c | ||
| udp_bpf.c | ||
| udp_diag.c | ||
| udp_impl.h | ||
| udp_offload.c | ||
| udp_tunnel_core.c | ||
| udp_tunnel_nic.c | ||
| udp_tunnel_stub.c | ||
| udp.c | ||
| udplite.c | ||
| xfrm4_input.c | ||
| xfrm4_output.c | ||
| xfrm4_policy.c | ||
| xfrm4_protocol.c | ||
| xfrm4_state.c | ||
| xfrm4_tunnel.c | ||