Message ID | 1352721866-16193-1-git-send-email-luis.henriques@canonical.com |
---|---|
State | New |
Headers | show |
On Mon, Nov 12, 2012 at 12:04:26PM +0000, Luis Henriques wrote: > From: Jesper Dangaard Brouer <brouer@redhat.com> > > BugLink: http://bugs.launchpad.net/bugs/1077091 > > Reading TCP stats when using TCP Illinois congestion control algorithm > can cause a divide by zero kernel oops. > > The division by zero occur in tcp_illinois_info() at: > do_div(t, ca->cnt_rtt); > where ca->cnt_rtt can become zero (when rtt_reset is called) > > Steps to Reproduce: > 1. Register tcp_illinois: > # sysctl -w net.ipv4.tcp_congestion_control=illinois > 2. Monitor internal TCP information via command "ss -i" > # watch -d ss -i > 3. Establish new TCP conn to machine > > Either it fails at the initial conn, or else it needs to wait > for a loss or a reset. > > This is only related to reading stats. The function avg_delay() also > performs the same divide, but is guarded with a (ca->cnt_rtt > 0) at its > calling point in update_params(). Thus, simply fix tcp_illinois_info(). > > Function tcp_illinois_info() / get_info() is called without > socket lock. Thus, eliminate any race condition on ca->cnt_rtt > by using a local stack variable. Simply reuse info.tcpv_rttcnt, > as its already set to ca->cnt_rtt. > Function avg_delay() is not affected by this race condition, as > its called with the socket lock. > > Cc: Petr Matousek <pmatouse@redhat.com> > Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com> > Acked-by: Eric Dumazet <edumazet@google.com> > Acked-by: Stephen Hemminger <shemminger@vyatta.com> > Signed-off-by: David S. Miller <davem@davemloft.net> > > (cherry picked from commit 8f363b77ee4fbf7c3bbcf5ec2c5ca482d396d664) > CVE-2012-4565 > Signed-off-by: Luis Henriques <luis.henriques@canonical.com> > --- > net/ipv4/tcp_illinois.c | 8 +++++--- > 1 file changed, 5 insertions(+), 3 deletions(-) > > diff --git a/net/ipv4/tcp_illinois.c b/net/ipv4/tcp_illinois.c > index 5aa5f54..f2c2ff0 100644 > --- a/net/ipv4/tcp_illinois.c > +++ b/net/ipv4/tcp_illinois.c > @@ -314,11 +314,13 @@ static void tcp_illinois_info(struct sock *sk, u32 ext, > .tcpv_rttcnt = ca->cnt_rtt, > .tcpv_minrtt = ca->base_rtt, > }; > - u64 t = ca->sum_rtt; > > - do_div(t, ca->cnt_rtt); > - info.tcpv_rtt = t; > + if (info.tcpv_rttcnt > 0) { > + u64 t = ca->sum_rtt; > > + do_div(t, info.tcpv_rttcnt); > + info.tcpv_rtt = t; > + } > nla_put(skb, INET_DIAG_VEGASINFO, sizeof(info), &info); > } > } That is a little subtle, using the copy already made in 'info' as a parameter to nla_put is a little unexpected. Otherwise it seems to do what is expected, to be race tollerant and, matches the upstream commit. Acked-by: Andy Whitcroft <apw@canonical.com> -apw
Applied to hardy, lucid, oneiric, precise, and quantal. -apw
diff --git a/net/ipv4/tcp_illinois.c b/net/ipv4/tcp_illinois.c index 5aa5f54..f2c2ff0 100644 --- a/net/ipv4/tcp_illinois.c +++ b/net/ipv4/tcp_illinois.c @@ -314,11 +314,13 @@ static void tcp_illinois_info(struct sock *sk, u32 ext, .tcpv_rttcnt = ca->cnt_rtt, .tcpv_minrtt = ca->base_rtt, }; - u64 t = ca->sum_rtt; - do_div(t, ca->cnt_rtt); - info.tcpv_rtt = t; + if (info.tcpv_rttcnt > 0) { + u64 t = ca->sum_rtt; + do_div(t, info.tcpv_rttcnt); + info.tcpv_rtt = t; + } nla_put(skb, INET_DIAG_VEGASINFO, sizeof(info), &info); } }