Re: [PATCH v3] xfrm: policy: Fix doulbe free in xfrm_policy_timer

Timo Teras
2020-03-23T08:00:30Z

On Mon, 23 Mar 2020 15:32:39 +0800
YueHaibing <yuehaibing@huawei.com> wrote:

> 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>

> ---
> v3: Only lock 'policy->walk.dead'
> 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..8a4af86a285e 100644
> --- a/net/xfrm/xfrm_policy.c
> +++ b/net/xfrm/xfrm_policy.c
> @@ -434,7 +434,9 @@ 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);
>
> --
> 2.17.1
>
>