af_unix: limit unix_tot_inflight, CVE-2010-4249
 

From: Eric Dumazet <eric.dumazet@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@gmail.com>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Brad Figg <brad.figg@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 040f952..26d22aa 100644
--- a/net/unix/garbage.c
+++ b/net/unix/garbage.c
@@ -168,9 +168,16 @@ static void maybe_unmark_and_push(struct sock *x)


static int gc_in_progress = 0;
+#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 (atomic_read(&unix_tot_inflight) > UNIX_INFLIGHT_TRIGGER_GC && !gc_in_progress)
+ unix_gc();
wait_event(unix_gc_wait, gc_in_progress == 0);
}

--
1.7.0.4


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