netdev - Re: [PATCH bpf 1/3] devmap: Fix premature entry free on destroying map

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Message-ID: <87muikb9ev.fsf@toke.dk>
Date:   Fri, 14 Jun 2019 15:09:44 +0200
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     Toshiaki Makita <toshiaki.makita1@...il.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>
Cc:     netdev@...r.kernel.org, xdp-newbies@...r.kernel.org,
        bpf@...r.kernel.org, "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        David Ahern <dsahern@...il.com>
Subject: Re: [PATCH bpf 1/3] devmap: Fix premature entry free on destroying map

Toshiaki Makita <toshiaki.makita1@...il.com> writes:

> On 19/06/14 (金) 21:10:38, Toke Høiland-Jørgensen wrote:
>> Toke Høiland-Jørgensen <toke@...hat.com> writes:
>> 
>>> Toshiaki Makita <toshiaki.makita1@...il.com> writes:
>>>
>>>> dev_map_free() waits for flush_needed bitmap to be empty in order to
>>>> ensure all flush operations have completed before freeing its entries.
>>>> However the corresponding clear_bit() was called before using the
>>>> entries, so the entries could be used after free.
>>>>
>>>> All access to the entries needs to be done before clearing the bit.
>>>> It seems commit a5e2da6e9787 ("bpf: netdev is never null in
>>>> __dev_map_flush") accidentally changed the clear_bit() and memory access
>>>> order.
>>>>
>>>> Note that the problem happens only in __dev_map_flush(), not in
>>>> dev_map_flush_old(). dev_map_flush_old() is called only after nulling
>>>> out the corresponding netdev_map entry, so dev_map_free() never frees
>>>> the entry thus no such race happens there.
>>>>
>>>> Fixes: a5e2da6e9787 ("bpf: netdev is never null in __dev_map_flush")
>>>> Signed-off-by: Toshiaki Makita <toshiaki.makita1@...il.com>
>>>
>>> I recently posted a patch[0] that gets rid of the bitmap entirely, so I
>>> think you can drop this one...
>> 
>> Alternatively, since this entire series should probably go to stable, I
>> can respin mine on top of it?
>
> Indeed conflict will happen, as this is for 'bpf' not 'bpf-next'.
> Sorry for disturbing your work.

Oh, no worries!

> I'm also not sure how to proceed in this case.

I guess we'll leave that up to the maintainers :)

-Toke