linux-kernel - [34-longterm 142/209] af_unix: limit unix_tot

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Message-Id: <1302803767-9715-29-git-send-email-paul.gortmaker@windriver.com>
Date:	Thu, 14 Apr 2011 13:55:00 -0400
From:	Paul Gortmaker <paul.gortmaker@...driver.com>
To:	stable@...nel.org, linux-kernel@...r.kernel.org
Cc:	stable-review@...nel.org, Eric Dumazet <eric.dumazet@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	Paul Gortmaker <paul.gortmaker@...driver.com>
Subject: [34-longterm 142/209] af_unix: limit unix_tot_inflight

From: Eric Dumazet <eric.dumazet@...il.com>

  =====================================================================
  | This is a commit scheduled for the next v2.6.34 longterm release. |
  | If you see a problem with using this for longterm, please comment.|
  =====================================================================

commit 9915672d41273f5b77f1b3c29b391ffb7732b84b upstream

Vegard Nossum found a unix socket OOM was possible, posting an exploit
program.

My analysis is we can eat all LOWMEM memory before unix_gc() being
called from unix_release_sock(). Moreover, the thread blocked in
unix_gc() can consume huge amount of time to perform cleanup because of
huge working set.

One way to handle this is to have a sensible limit on unix_tot_inflight,
tested from wait_for_unix_gc() and to force a call to unix_gc() if this
limit is hit.

This solves the OOM and also reduce overall latencies, and should not
slowdown normal workloads.

Reported-by: Vegard Nossum <vegard.nossum@...il.com>
Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Paul Gortmaker <paul.gortmaker@...driver.com>
---
 net/unix/garbage.c |    7 +++++++
 1 files changed, 7 insertions(+), 0 deletions(-)

diff --git a/net/unix/garbage.c b/net/unix/garbage.c
index 14c22c3..ef5aa55 100644
--- a/net/unix/garbage.c
+++ b/net/unix/garbage.c
@@ -268,9 +268,16 @@ static void inc_inflight_move_tail(struct unix_sock *u)
 }

 static bool gc_in_progress = false;
+#define UNIX_INFLIGHT_TRIGGER_GC 16000

 void wait_for_unix_gc(void)
 {
+	/*
+	 * If number of inflight sockets is insane,
+	 * force a garbage collect right now.
+	 */
+	if (unix_tot_inflight > UNIX_INFLIGHT_TRIGGER_GC && !gc_in_progress)
+		unix_gc();
 	wait_event(unix_gc_wait, gc_in_progress == false);
 }

-- 
1.7.4.4

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