linux-kernel - Re: [PATCH v7 10/10] lib/dlock-list: Fix use-after-unlock problem in dlist_for_each_entry

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Message-ID: <0fc66521-2a5f-1dc3-bd37-784a1435c7a8@redhat.com>
Date:   Mon, 30 Oct 2017 10:15:04 -0400
From:   Waiman Long <longman@...hat.com>
To:     Davidlohr Bueso <dave@...olabs.net>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>, Jan Kara <jack@...e.com>,
        Jeff Layton <jlayton@...chiereds.net>,
        "J. Bruce Fields" <bfields@...ldses.org>,
        Tejun Heo <tj@...nel.org>,
        Christoph Lameter <cl@...ux-foundation.org>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andi Kleen <andi@...stfloor.org>,
        Dave Chinner <dchinner@...hat.com>,
        Boqun Feng <boqun.feng@...il.com>
Subject: Re: [PATCH v7 10/10] lib/dlock-list: Fix use-after-unlock problem in
 dlist_for_each_entry_safe()

On 10/30/2017 10:11 AM, Davidlohr Bueso wrote:
> On Fri, 27 Oct 2017, Waiman Long wrote:
>
>> The dlist_for_each_entry_safe() macro in include/linux/dlock-list has
>> a use-after-unlock problem where racing condition can happen because
>> of a lack of spinlock protection.  Fortunately, this macro is not
>> currently being used in the kernel.
>>
>> This patch changes the dlist_for_each_entry_safe() macro so that the
>> call to __dlock_list_next_list() is deferred until the next entry is
>> being used. That should eliminate the use-after-unlock problem.
>>
>> Reported-by: Boqun Feng <boqun.feng@...il.com>
>> Signed-off-by: Waiman Long <longman@...hat.com>
>
> Reviewed-by: Davidlohr Bueso <dbueso@...e.de>
>
> But would it not be better to merge this patch (among others) into 1/N?
> Specifically the newer patches 7-10 should be in the original dlock
> implementation instead of adding fixes to incorrect code in the original
> commit. Also less of a pita for backporting.
>
> Thanks,
> Davidlohr +191,17 @@ extern void dlock_list_add(struct dlock_list_node
> *node,

Yes, that is true. I will send out a new version with all the fixes
integrated later this week.

Cheers,
Longman