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Date:   Sun, 8 Sep 2019 13:28:22 +0200
From:   Jesper Dangaard Brouer <brouer@redhat.com>
To:     Toke =?UTF-8?B?SMO4aWxhbmQtSsO4cmdlbnNlbg==?= <toke@redhat.com>
Cc:     brouer@redhat.com, ast@kernel.org, bpf@vger.kernel.org,
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        kafai@fb.com, linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
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        syzbot+4e7a85b1432052e8d6f8@syzkaller.appspotmail.com
Subject: Re: [PATCH bpf-next] xdp: Fix race in dev_map_hash_update_elem()
 when replacing element
Message-ID: <20190908132822.5ac2fbe1@carbon>
In-Reply-To: <20190908082016.17214-1-toke@redhat.com>
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        <20190908082016.17214-1-toke@redhat.com>
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On Sun,  8 Sep 2019 09:20:16 +0100
Toke Høiland-Jørgensen <toke@redhat.com> wrote:

> syzbot found a crash in dev_map_hash_update_elem(), when replacing an
> element with a new one. Jesper correctly identified the cause of the crash
> as a race condition between the initial lookup in the map (which is done
> before taking the lock), and the removal of the old element.
> 
> Rather than just add a second lookup into the hashmap after taking the
> lock, fix this by reworking the function logic to take the lock before the
> initial lookup.
> 
> Fixes: 6f9d451ab1a3 ("xdp: Add devmap_hash map type for looking up devices by hashed index")
> Reported-and-tested-by: syzbot+4e7a85b1432052e8d6f8@syzkaller.appspotmail.com
> Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>

Acked-by: Jesper Dangaard Brouer <brouer@redhat.com>

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer