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

Steffen Klassert
2020-03-25T12:54:02Z

On Mon, Mar 23, 2020 at 03:32:39PM +0800, YueHaibing 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>
> ---
> v3: Only lock 'policy->walk.dead'
> v2: Fix typo 'write_lock_bh'--> 'write_unlock_bh' while unlocking
> ---

Applied, thanks everyone!