linux-kernel - Re: KASAN: use-after-free Read in __rhashtable

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Date:   Fri, 24 Aug 2018 16:50:48 -0700
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Sowmini Varadhan <sowmini.varadhan@...cle.com>
Cc:     syzbot <syzbot+8967084bcac563795dc6@...kaller.appspotmail.com>,
        David Miller <davem@...emloft.net>,
        LKML <linux-kernel@...r.kernel.org>, linux-rdma@...r.kernel.org,
        netdev <netdev@...r.kernel.org>, rds-devel@....oracle.com,
        Santosh Shilimkar <santosh.shilimkar@...cle.com>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>
Subject: Re: KASAN: use-after-free Read in __rhashtable_lookup (2)

On Fri, Aug 24, 2018 at 4:37 PM, Sowmini Varadhan
<sowmini.varadhan@...cle.com> wrote:
> On (08/24/18 16:10), Dmitry Vyukov wrote:
>> You need a colon after dup.
>
> I see.
>
>> But this can't possibly be a dup of that bug. That bug was fixed in February:
>
> Apologies, I unknowingly made a mistake in my
> syzbot-tiquette in that case,
>
> I did not intend to *close* the bug as a dup, I was
> merely trying to indicate that this is yet another
> manifestation of the original report with subject
> "KASAN: use-after-free Read in rds_find_bound"
>
> All of these problems are happening because we are missing
> a synchronize_net() in rds_release.
>
> A full description of the race conditon can be found in
> https://www.spinics.net/lists/netdev/msg475074.html
>
> If rds_release is going to nuke the rds_socket
> it needs to sychronize_net() with other threads that may be
> looking up the bind_hash_table. If we dont do that,
> all of these "use-after-free" races can happen.
> As long as we dont have the synchronize_net() we are
> missing a big (and standard) bit of RCU synchronization.


If it's a note for humans, then just a plain English comment will do.