Re: [PATCH bpf-next] xdp: Fix race in dev_map_hash_update_elem() when replacing element

From: Jesper Dangaard Brouer
Date: Sun Sep 08 2019 - 07:28:44 EST

On Sun, 8 Sep 2019 09:20:16 +0100
Toke HÃiland-JÃrgensen <toke@xxxxxxxxxx> 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@xxxxxxxxxxxxxxxxxxxxxxxxx
> Signed-off-by: Toke HÃiland-JÃrgensen <toke@xxxxxxxxxx>

Acked-by: Jesper Dangaard Brouer <brouer@xxxxxxxxxx>

Best regards,
Jesper Dangaard Brouer
MSc.CS, Principal Kernel Engineer at Red Hat