[34-longterm 142/209] af_unix: limit unix_tot_inflight

From: Paul Gortmaker
Date: Thu Apr 14 2011 - 14:17:04 EST

From: Eric Dumazet <eric.dumazet@xxxxxxxxx>

| 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

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@xxxxxxxxx>
Signed-off-by: Eric Dumazet <eric.dumazet@xxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx>
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;

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);


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