[PATCH] ipv4: fix the rcu race between free_fib_info and ip_route_output_slow

["kun.jiang" <kunx.jiang@xxxxxxxxx>]

From: Yanmin Zhang <yanmin_zhang@xxxxxxxxxxxxxxx>

We hit a kernel OOPS.

<3>[23898.789643] BUG: sleeping function called from invalid context at
/data/buildbot/workdir/ics/hardware/intel/linux-2.6/arch/x86/mm/fault.c:1103
<3>[23898.862215] in_atomic(): 0, irqs_disabled(): 0, pid: 10526, name:
Thread-6683
<4>[23898.967805] HSU serial 0000:00:05.1: 0000:00:05.2:HSU serial prevented me
to suspend...
<4>[23899.258526] Pid: 10526, comm: Thread-6683 Tainted: G        W
3.0.8-137685-ge7742f9 #1
<4>[23899.357404] HSU serial 0000:00:05.1: 0000:00:05.2:HSU serial prevented me
to suspend...
<4>[23899.904225] Call Trace:
<4>[23899.989209]  [<c1227f50>] ? pgtable_bad+0x130/0x130
<4>[23900.000416]  [<c1238c2a>] __might_sleep+0x10a/0x110
<4>[23900.007357]  [<c1228021>] do_page_fault+0xd1/0x3c0
<4>[23900.013764]  [<c18e9ba9>] ? restore_all+0xf/0xf
<4>[23900.024024]  [<c17c007b>] ? napi_complete+0x8b/0x690
<4>[23900.029297]  [<c1227f50>] ? pgtable_bad+0x130/0x130
<4>[23900.123739]  [<c1227f50>] ? pgtable_bad+0x130/0x130
<4>[23900.128955]  [<c18ea0c3>] error_code+0x5f/0x64
<4>[23900.133466]  [<c1227f50>] ? pgtable_bad+0x130/0x130
<4>[23900.138450]  [<c17f6298>] ? __ip_route_output_key+0x698/0x7c0
<4>[23900.144312]  [<c17f5f8d>] ? __ip_route_output_key+0x38d/0x7c0
<4>[23900.150730]  [<c17f63df>] ip_route_output_flow+0x1f/0x60
<4>[23900.156261]  [<c181de58>] ip4_datagram_connect+0x188/0x2b0
<4>[23900.161960]  [<c18e981f>] ? _raw_spin_unlock_bh+0x1f/0x30
<4>[23900.167834]  [<c18298d6>] inet_dgram_connect+0x36/0x80
<4>[23900.173224]  [<c14f9e88>] ? _copy_from_user+0x48/0x140
<4>[23900.178817]  [<c17ab9da>] sys_connect+0x9a/0xd0
<4>[23900.183538]  [<c132e93c>] ? alloc_file+0xdc/0x240
<4>[23900.189111]  [<c123925d>] ? sub_preempt_count+0x3d/0x50

In function free_fib_info, we don't reset nexthop_nh->nh_dev to NULL before releasing
nh_dev. kfree_rcu(fi, rcu) would release the whole area.

Signed-off-by: Yanmin Zhang <yanmin_zhang@xxxxxxxxxxxxxxx>
Signed-off-by: Kun Jiang <kunx.jiang@xxxxxxxxx>
---
 net/ipv4/fib_semantics.c |    1 -
 1 files changed, 0 insertions(+), 1 deletions(-)

diff --git a/net/ipv4/fib_semantics.c b/net/ipv4/fib_semantics.c
index 5063fa3..68ea013 100644
--- a/net/ipv4/fib_semantics.c
+++ b/net/ipv4/fib_semantics.c
@@ -159,7 +159,6 @@ void free_fib_info(struct fib_info *fi)
 	change_nexthops(fi) {
 		if (nexthop_nh->nh_dev)
 			dev_put(nexthop_nh->nh_dev);
-		nexthop_nh->nh_dev = NULL;
 	} endfor_nexthops(fi);
 	fib_info_cnt--;
 	release_net(fi->fib_net);
-- 
1.7.1
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