[PATCH v2] xfrm: policy: Fix doulbe free in xfrm_policy_timer

YueHaibing
2020-03-23T01:45:10Z

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>
---
v2: Fix typo 'write_lock_bh'--> 'write_unlock_bh' while unlocking
---
net/xfrm/xfrm_policy.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
index dbda08ec566e..ae0689174bbf 100644
--- a/net/xfrm/xfrm_policy.c
+++ b/net/xfrm/xfrm_policy.c
@@ -434,6 +434,7 @@ EXPORT_SYMBOL(xfrm_policy_destroy);

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

atomic_inc(&policy->genid);
@@ -445,6 +446,7 @@ static void xfrm_policy_kill(struct xfrm_policy *policy)
if (del_timer(&policy->timer))
xfrm_pol_put(policy);

+ write_unlock_bh(&policy->lock);
xfrm_pol_put(policy);
}

--
2.17.1