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

[Steffen Klassert]

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@xxxxxxxxxx>
> ---
> v3: Only lock 'policy->walk.dead'
> v2: Fix typo 'write_lock_bh'--> 'write_unlock_bh' while unlocking
> ---

Applied, thanks everyone!