[PATCH 5.4 118/155] xfrm: policy: Fix doulbe free in xfrm_policy_timer

Greg Kroah-Hartman
2020-03-31T09:17:03Z

From: YueHaibing <yuehaibing@huawei.com>

commit 4c59406ed00379c8663f8663d82b2537467ce9d7 upstream.

After xfrm_add_policy add a policy, its ref is 2, then

xfrm_policy_timer
read_lock
xp->walk.dead is 0
....
mod_timer()
xfrm_policy_kill
policy->walk.dead = 1
....
del_timer(&policy->timer)
xfrm_pol_put //ref is 1
xfrm_pol_put //ref is 0
xfrm_policy_destroy
call_rcu
xfrm_pol_hold //ref is 1
read_unlock
xfrm_pol_put //ref is 0
xfrm_policy_destroy
call_rcu

xfrm_policy_destroy is called twice, which may leads to
double free.

Call Trace:
RIP: 0010:refcount_warn_saturate+0x161/0x210
...
xfrm_policy_timer+0x522/0x600
call_timer_fn+0x1b3/0x5e0
? __xfrm_decode_session+0x2990/0x2990
? msleep+0xb0/0xb0
? _raw_spin_unlock_irq+0x24/0x40
? __xfrm_decode_session+0x2990/0x2990
? __xfrm_decode_session+0x2990/0x2990
run_timer_softirq+0x5c5/0x10e0

Fix this by use write_lock_bh in xfrm_policy_kill.

Fixes: ea2dea9dacc2 ("xfrm: remove policy lock when accessing policy->walk.dead")
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Acked-by: Timo Teräs <timo.teras@iki.fi>
Acked-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
net/xfrm/xfrm_policy.c | 2 ++
1 file changed, 2 insertions(+)

--- a/net/xfrm/xfrm_policy.c
+++ b/net/xfrm/xfrm_policy.c
@@ -431,7 +431,9 @@ EXPORT_SYMBOL(xfrm_policy_destroy);

static void xfrm_policy_kill(struct xfrm_policy *policy)
{
+ write_lock_bh(&policy->lock);
policy->walk.dead = 1;
+ write_unlock_bh(&policy->lock);

atomic_inc(&policy->genid);