linux/net
Yuchung Cheng 8b8a321ff7 tcp: fix zero cwnd in tcp_cwnd_reduction
Patch 3759824da8 ("tcp: PRR uses CRB mode by default and SS mode
conditionally") introduced a bug that cwnd may become 0 when both
inflight and sndcnt are 0 (cwnd = inflight + sndcnt). This may lead
to a div-by-zero if the connection starts another cwnd reduction
phase by setting tp->prior_cwnd to the current cwnd (0) in
tcp_init_cwnd_reduction().

To prevent this we skip PRR operation when nothing is acked or
sacked. Then cwnd must be positive in all cases as long as ssthresh
is positive:

1) The proportional reduction mode
   inflight > ssthresh > 0

2) The reduction bound mode
  a) inflight == ssthresh > 0

  b) inflight < ssthresh
     sndcnt > 0 since newly_acked_sacked > 0 and inflight < ssthresh

Therefore in all cases inflight and sndcnt can not both be 0.
We check invalid tp->prior_cwnd to avoid potential div0 bugs.

In reality this bug is triggered only with a sequence of less common
events.  For example, the connection is terminating an ECN-triggered
cwnd reduction with an inflight 0, then it receives reordered/old
ACKs or DSACKs from prior transmission (which acks nothing). Or the
connection is in fast recovery stage that marks everything lost,
but fails to retransmit due to local issues, then receives data
packets from other end which acks nothing.

Fixes: 3759824da8 ("tcp: PRR uses CRB mode by default and SS mode conditionally")
Reported-by: Oleksandr Natalenko <oleksandr@natalenko.name>
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
2016-01-06 16:39:56 -05:00
..
6lowpan 6lowpan: put mcast compression in an own function 2015-10-21 00:49:25 +02:00
9p IB/cma: Add support for network namespaces 2015-10-28 12:32:48 -04:00
802
8021q vlan: Do not put vlan headers back on bridge and macvlan ports 2015-11-17 14:38:35 -05:00
appletalk
atm atm: deal with setting entry before mkip was called 2015-09-17 22:13:32 -07:00
ax25 net: add validation for the socket syscall protocol argument 2015-12-14 16:09:30 -05:00
batman-adv batman-adv: Fix invalid stack access in batadv_dat_select_candidates 2015-12-07 22:40:21 +08:00
bluetooth bluetooth: Validate socket address length in sco_sock_bind(). 2015-12-15 15:39:08 -05:00
bridge bridge: Only call /sbin/bridge-stp for the initial network namespace 2016-01-05 16:46:17 -05:00
caif net: rename SOCK_ASYNC_NOSPACE and SOCK_ASYNC_WAITDATA 2015-12-01 15:45:05 -05:00
can can: avoid using timeval for uapi 2015-10-13 17:42:34 +02:00
ceph Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/sage/ceph-client 2015-11-13 09:24:40 -08:00
core net: possible use after free in dst_release 2016-01-06 15:00:27 -05:00
dcb net/dcb: make dcbnl.c explicitly non-modular 2015-10-09 07:52:27 -07:00
dccp ipv6: kill sk_dst_lock 2015-12-03 11:32:06 -05:00
decnet net: add validation for the socket syscall protocol argument 2015-12-14 16:09:30 -05:00
dns_resolver net: dns_resolver: convert time_t to time64_t 2015-11-18 16:27:46 -05:00
dsa net: dsa: use switchdev obj for VLAN add/del ops 2015-11-01 15:56:11 -05:00
ethernet net: help compiler generate better code in eth_get_headlen 2015-09-28 22:51:15 -07:00
hsr net/hsr: fix a warning message 2015-11-23 14:56:15 -05:00
ieee802154 net: fix percpu memory leaks 2015-11-02 22:47:14 -05:00
ipv4 tcp: fix zero cwnd in tcp_cwnd_reduction 2016-01-06 16:39:56 -05:00
ipv6 ipv6: honor ifindex in case we receive ll addresses in router advertisements 2015-12-23 22:03:54 -05:00
ipx
irda net: add validation for the socket syscall protocol argument 2015-12-14 16:09:30 -05:00
iucv net: rename SOCK_ASYNC_NOSPACE and SOCK_ASYNC_WAITDATA 2015-12-01 15:45:05 -05:00
key af_key: fix two typos 2015-10-23 03:05:19 -07:00
l2tp ipv6: add complete rcu protection around np->opt 2015-12-02 23:37:16 -05:00
l3mdev net: Add netif_is_l3_slave 2015-10-07 04:27:43 -07:00
lapb
llc tcp: fix recv with flags MSG_WAITALL | MSG_PEEK 2015-07-27 01:06:53 -07:00
mac80211 mac80211: handle width changes from opmode notification IE in beacon 2015-12-15 13:16:47 +01:00
mac802154 mac802154: llsec: use kzfree 2015-10-21 00:49:24 +02:00
mpls mpls: make via address optional for multipath routes 2015-12-12 00:43:44 -05:00
netfilter netfilter: nft_ct: include direction when dumping NFT_CT_L3PROTOCOL key 2015-12-18 14:45:45 +01:00
netlabel
netlink mm, page_alloc: distinguish between being unable to sleep, unwilling to sleep and avoiding waking kswapd 2015-11-06 17:50:42 -08:00
netrom netfilter: Remove spurios included of netfilter.h 2015-06-18 21:14:32 +02:00
nfc net: rename SOCK_ASYNC_NOSPACE and SOCK_ASYNC_WAITDATA 2015-12-01 15:45:05 -05:00
openvswitch openvswitch: Fix template leak in error cases. 2015-12-29 15:27:52 -05:00
packet packet: Allow packets with only a header (but no payload) 2015-11-29 22:17:17 -05:00
phonet
rds RDS: fix race condition when sending a message on unbound socket 2015-11-24 17:20:09 -05:00
rfkill rfkill: copy the name into the rfkill struct 2015-12-10 10:37:51 +01:00
rose Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2015-06-24 02:58:51 -07:00
rxrpc net: rename SOCK_ASYNC_NOSPACE and SOCK_ASYNC_WAITDATA 2015-12-01 15:45:05 -05:00
sched net: sched: fix missing free per cpu on qstats 2016-01-06 01:40:21 -05:00
sctp sctp: sctp should release assoc when sctp_make_abort_user return NULL in sctp_close 2015-12-30 16:57:16 -05:00
sunrpc sched/wait: Fix the signal handling fix 2015-12-13 14:30:59 -08:00
switchdev switchdev: respect SKIP_EOPNOTSUPP flag in case there is no recursion 2015-11-03 13:39:21 -05:00
tipc tipc: fix error handling of expanding buffer headroom 2015-11-24 11:26:19 -05:00
unix af_unix: Fix splice-bind deadlock 2016-01-04 23:22:49 -05:00
vmw_vsock VSOCK: call sk->sk_data_ready() on accept() 2015-11-04 22:03:10 -05:00
wimax net:wimax: Fix doucble word "the the" in networking.xml 2015-08-09 22:43:52 -07:00
wireless nl80211: Fix potential memory leak in nl80211_connect 2015-12-15 13:11:26 +01:00
x25
xfrm Merge branch 'master' of git://git.kernel.org/pub/scm/linux/kernel/git/klassert/ipsec 2015-12-22 16:26:31 -05:00
compat.c
Kconfig net: Introduce L3 Master device abstraction 2015-09-29 20:40:32 -07:00
Makefile net: Introduce L3 Master device abstraction 2015-09-29 20:40:32 -07:00
socket.c net, socket, socket_wq: fix missing initialization of flags 2015-12-30 16:38:01 -05:00
sysctl_net.c net: sysctl: fix a kmemleak warning 2015-10-23 06:22:08 -07:00