This is a note to let you know that I've just added the patch titled
ipv4: fix race in concurrent ip_route_input_slow()
to the 3.12-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
ipv4-fix-race-in-concurrent-ip_route_input_slow.patch
and it can be found in the queue-3.12 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <[email protected]> know about it.
>From foo@baz Thu Dec 5 16:16:39 PST 2013
From: Alexei Starovoitov <[email protected]>
Date: Tue, 19 Nov 2013 19:12:34 -0800
Subject: ipv4: fix race in concurrent ip_route_input_slow()
From: Alexei Starovoitov <[email protected]>
[ Upstream commit dcdfdf56b4a6c9437fc37dbc9cee94a788f9b0c4 ]
CPUs can ask for local route via ip_route_input_noref() concurrently.
if nh_rth_input is not cached yet, CPUs will proceed to allocate
equivalent DSTs on 'lo' and then will try to cache them in nh_rth_input
via rt_cache_route()
Most of the time they succeed, but on occasion the following two lines:
orig = *p;
prev = cmpxchg(p, orig, rt);
in rt_cache_route() do race and one of the cpus fails to complete cmpxchg.
But ip_route_input_slow() doesn't check the return code of rt_cache_route(),
so dst is leaking. dst_destroy() is never called and 'lo' device
refcnt doesn't go to zero, which can be seen in the logs as:
unregister_netdevice: waiting for lo to become free. Usage count = 1
Adding mdelay() between above two lines makes it easily reproducible.
Fix it similar to nh_pcpu_rth_output case.
Fixes: d2d68ba9fe8b ("ipv4: Cache input routes in fib_info nexthops.")
Signed-off-by: Alexei Starovoitov <[email protected]>
Signed-off-by: David S. Miller <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
net/ipv4/route.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -1772,8 +1772,12 @@ local_input:
rth->dst.error= -err;
rth->rt_flags &= ~RTCF_LOCAL;
}
- if (do_cache)
- rt_cache_route(&FIB_RES_NH(res), rth);
+ if (do_cache) {
+ if (unlikely(!rt_cache_route(&FIB_RES_NH(res), rth))) {
+ rth->dst.flags |= DST_NOCACHE;
+ rt_add_uncached_list(rth);
+ }
+ }
skb_dst_set(skb, &rth->dst);
err = 0;
goto out;
Patches currently in stable-queue which might be from [email protected] are
queue-3.12/core-dev-do-not-ignore-dmac-in-dev_forward_skb.patch
queue-3.12/net-x86-bpf-don-t-forget-to-free-sk_filter-v2.patch
queue-3.12/ipv4-fix-race-in-concurrent-ip_route_input_slow.patch
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