[PATCH 1/6] af_unix: limit unix_tot_inflight CVE-2010-4249

[paolo.pisati at canonical.com]

From: Eric Dumazet <eric.dumazet at gmail.com>

CVE-2010-4249

BugLink: http://bugs.launchpad.net/bugs/769182

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 at gmail.com>
Signed-off-by: Eric Dumazet <eric.dumazet at gmail.com>
Signed-off-by: David S. Miller <davem at davemloft.net>
Signed-off-by: Brad Figg <brad.figg at canonical.com>
Signed-off-by: Paolo Pisati <paolo.pisati at canonical.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 07499a5..dc2cb61 100644
--- a/net/unix/garbage.c
+++ b/net/unix/garbage.c
@@ -269,9 +269,16 @@ 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);
 }
 
-- 
1.7.4.1