118 lines
4.6 KiB
Diff
118 lines
4.6 KiB
Diff
Path: news.gmane.org!not-for-mail
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From: Jesper Dangaard Brouer <brouer@redhat.com>
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Newsgroups: gmane.linux.network
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Subject: [net PATCH V2] net: fix divide by zero in tcp algorithm illinois
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Date: Wed, 31 Oct 2012 13:45:32 +0100
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Lines: 63
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Approved: news@gmane.org
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Message-ID: <20121031124318.30915.32293.stgit@dragon>
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NNTP-Posting-Date: Wed, 31 Oct 2012 12:44:32 +0000 (UTC)
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Cc: Jesper Dangaard Brouer <brouer@redhat.com>, netdev@vger.kernel.org,
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Petr Matousek <pmatouse@redhat.com>,
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Stephen Hemminger <shemminger@vyatta.com>,
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Eric Dumazet <eric.dumazet@gmail.com>
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To: "David S. Miller" <davem@davemloft.net>
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Xref: news.gmane.org gmane.linux.network:247871
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Archived-At: <http://permalink.gmane.org/gmane.linux.network/247871>
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Reading TCP stats when using TCP Illinois congestion control algorithm
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can cause a divide by zero kernel oops.
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The division by zero occur in tcp_illinois_info() at:
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do_div(t, ca->cnt_rtt);
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where ca->cnt_rtt can become zero (when rtt_reset is called)
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Steps to Reproduce:
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1. Register tcp_illinois:
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# sysctl -w net.ipv4.tcp_congestion_control=illinois
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2. Monitor internal TCP information via command "ss -i"
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# watch -d ss -i
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3. Establish new TCP conn to machine
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Either it fails at the initial conn, or else it needs to wait
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for a loss or a reset.
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This is only related to reading stats. The function avg_delay() also
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performs the same divide, but is guarded with a (ca->cnt_rtt > 0) at its
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calling point in update_params(). Thus, simply fix tcp_illinois_info().
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Function tcp_illinois_info() / get_info() is called without
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socket lock. Thus, eliminate any race condition on ca->cnt_rtt
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by using a local stack variable. Simply reuse info.tcpv_rttcnt,
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as its already set to ca->cnt_rtt.
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Function avg_delay() is not affected by this race condition, as
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its called with the socket lock.
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Cc: Petr Matousek <pmatouse@redhat.com>
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Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
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---
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V2:
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Address Eric Dumazets input:
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- Save 2 bytes of stack, by using info.tcpv_rttcnt.
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- Help compiler, and define "u64 t" inside if() lexical scope.
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net/ipv4/tcp_illinois.c | 8 +++++---
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1 files changed, 5 insertions(+), 3 deletions(-)
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diff --git a/net/ipv4/tcp_illinois.c b/net/ipv4/tcp_illinois.c
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index 813b43a..834857f 100644
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--- a/net/ipv4/tcp_illinois.c
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+++ b/net/ipv4/tcp_illinois.c
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@@ -313,11 +313,13 @@ static void tcp_illinois_info(struct sock *sk, u32 ext,
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.tcpv_rttcnt = ca->cnt_rtt,
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.tcpv_minrtt = ca->base_rtt,
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};
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- u64 t = ca->sum_rtt;
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- do_div(t, ca->cnt_rtt);
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- info.tcpv_rtt = t;
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+ if (info.tcpv_rttcnt > 0) {
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+ u64 t = ca->sum_rtt;
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+ do_div(t, info.tcpv_rttcnt);
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+ info.tcpv_rtt = t;
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+ }
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nla_put(skb, INET_DIAG_VEGASINFO, sizeof(info), &info);
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}
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}
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