linux-kernel - Re: [PATCH bpf-next] xdp: Fix race in dev_map_hash_update

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Message-ID: <20190908132822.5ac2fbe1@carbon>
Date:   Sun, 8 Sep 2019 13:28:22 +0200
From:   Jesper Dangaard Brouer <brouer@...hat.com>
To:     Toke Høiland-Jørgensen <toke@...hat.com>
Cc:     brouer@...hat.com, ast@...nel.org, bpf@...r.kernel.org,
        daniel@...earbox.net, davem@...emloft.net, hawk@...nel.org,
        jakub.kicinski@...ronome.com, john.fastabend@...il.com,
        kafai@...com, linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        songliubraving@...com, syzkaller-bugs@...glegroups.com, yhs@...com,
        syzbot+4e7a85b1432052e8d6f8@...kaller.appspotmail.com
Subject: Re: [PATCH bpf-next] xdp: Fix race in dev_map_hash_update_elem()
 when replacing element

On Sun,  8 Sep 2019 09:20:16 +0100
Toke Høiland-Jørgensen <toke@...hat.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@...kaller.appspotmail.com
> Signed-off-by: Toke Høiland-Jørgensen <toke@...hat.com>

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

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