netdev - Re: [PATCH net] net: sched: act_sample: fix psample group handling on overwrite

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Message-Id: <20190828.155430.2117344085860709411.davem@davemloft.net>
Date:   Wed, 28 Aug 2019 15:54:30 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     vladbu@...lanox.com
Cc:     netdev@...r.kernel.org, jhs@...atatu.com, xiyou.wangcong@...il.com,
        jiri@...nulli.us, dcaratti@...hat.com
Subject: Re: [PATCH net] net: sched: act_sample: fix psample group handling
 on overwrite

From: Vlad Buslov <vladbu@...lanox.com>
Date: Tue, 27 Aug 2019 21:49:38 +0300

> Action sample doesn't properly handle psample_group pointer in overwrite
> case. Following issues need to be fixed:
> 
> - In tcf_sample_init() function RCU_INIT_POINTER() is used to set
>   s->psample_group, even though we neither setting the pointer to NULL, nor
>   preventing concurrent readers from accessing the pointer in some way.
>   Use rcu_swap_protected() instead to safely reset the pointer.
> 
> - Old value of s->psample_group is not released or deallocated in any way,
>   which results resource leak. Use psample_group_put() on non-NULL value
>   obtained with rcu_swap_protected().
> 
> - The function psample_group_put() that released reference to struct
>   psample_group pointed by rcu-pointer s->psample_group doesn't respect rcu
>   grace period when deallocating it. Extend struct psample_group with rcu
>   head and use kfree_rcu when freeing it.
> 
> Fixes: 5c5670fae430 ("net/sched: Introduce sample tc action")
> Signed-off-by: Vlad Buslov <vladbu@...lanox.com>

Applied and queued up for -stable.