netdev - Re: [PATCH bpf-next v8 04/12] bpf: Only reply field should be writeable

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Message-ID: <a4a58189-0a6a-5af8-d323-1c8086a88cbc@fb.com>
Date:   Wed, 24 Jan 2018 12:23:10 -0800
From:   Alexei Starovoitov <ast@...com>
To:     Yuchung Cheng <ycheng@...gle.com>, Lawrence Brakmo <brakmo@...com>
CC:     netdev <netdev@...r.kernel.org>, Kernel Team <kernel-team@...com>,
        Blake Matheny <bmatheny@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Neal Cardwell <ncardwell@...gle.com>
Subject: Re: [PATCH bpf-next v8 04/12] bpf: Only reply field should be
 writeable

On 1/24/18 11:58 AM, Yuchung Cheng wrote:
> On Tue, Jan 23, 2018 at 11:57 PM, Lawrence Brakmo <brakmo@...com> wrote:
>> Currently, a sock_ops BPF program can write the op field and all the
>> reply fields (reply and replylong). This is a bug. The op field should
>> not have been writeable and there is currently no way to use replylong
>> field for indices >= 1. This patch enforces that only the reply field
>> (which equals replylong[0]) is writeable.
> Would this patch be more suitable for -net ?

yes. we will send it to 4.15 and 4.14 as soon as it's released.
See discussion with Eric.

>>
>> Fixes: 40304b2a1567 ("bpf: BPF support for sock_ops")
>> Signed-off-by: Lawrence Brakmo <brakmo@...com>
> Acked-by: Yuchung Cheng <ycheng@...gle.com>
>
>> ---
>>  net/core/filter.c | 3 +--
>>  1 file changed, 1 insertion(+), 2 deletions(-)
>>
>> diff --git a/net/core/filter.c b/net/core/filter.c
>> index 0cf170f..c356ec0 100644
>> --- a/net/core/filter.c
>> +++ b/net/core/filter.c
>> @@ -3845,8 +3845,7 @@ static bool sock_ops_is_valid_access(int off, int size,
>>  {
>>         if (type == BPF_WRITE) {
>>                 switch (off) {
>> -               case offsetof(struct bpf_sock_ops, op) ...
>> -                    offsetof(struct bpf_sock_ops, replylong[3]):
>> +               case offsetof(struct bpf_sock_ops, reply):
>>                         break;
>>                 default:
>>                         return false;
>> --
>> 2.9.5
>>