linux-kernel - Re: [PATCH bpf-next] bpf: check flags in 'bpf_ringbuf_discard()' and 'bpf_ringbuf

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Date:   Tue, 30 Mar 2021 18:12:21 +0000
From:   Song Liu <songliubraving@...com>
To:     Pedro Tammela <pctammela@...il.com>
CC:     Pedro Tammela <pctammela@...atatu.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>, Martin Lau <kafai@...com>,
        Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>, Shuah Khan <shuah@...nel.org>,
        Joe Stringer <joe@...ium.io>,
        Quentin Monnet <quentin@...valent.com>,
        Yang Li <yang.lee@...ux.alibaba.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>
Subject: Re: [PATCH bpf-next] bpf: check flags in 'bpf_ringbuf_discard()' and
 'bpf_ringbuf_submit()'



> On Mar 30, 2021, at 7:22 AM, Pedro Tammela <pctammela@...il.com> wrote:
> 
> Em seg., 29 de mar. de 2021 às 13:10, Song Liu <songliubraving@...com> escreveu:
>> 
>> 
>> 
>>> On Mar 28, 2021, at 9:10 AM, Pedro Tammela <pctammela@...il.com> wrote:
>>> 
>>> The current code only checks flags in 'bpf_ringbuf_output()'.
>>> 
>>> Signed-off-by: Pedro Tammela <pctammela@...atatu.com>
>>> ---
>>> include/uapi/linux/bpf.h       |  8 ++++----
>>> kernel/bpf/ringbuf.c           | 13 +++++++++++--
>>> tools/include/uapi/linux/bpf.h |  8 ++++----
>>> 3 files changed, 19 insertions(+), 10 deletions(-)
>>> 
>>> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
>>> index 100cb2e4c104..232b5e5dd045 100644
>>> --- a/include/uapi/linux/bpf.h
>>> +++ b/include/uapi/linux/bpf.h
>>> @@ -4073,7 +4073,7 @@ union bpf_attr {
>>> *            Valid pointer with *size* bytes of memory available; NULL,
>>> *            otherwise.
>>> *
>>> - * void bpf_ringbuf_submit(void *data, u64 flags)
>>> + * int bpf_ringbuf_submit(void *data, u64 flags)
>> 
>> This should be "long" instead of "int".
>> 
>>> *    Description
>>> *            Submit reserved ring buffer sample, pointed to by *data*.
>>> *            If **BPF_RB_NO_WAKEUP** is specified in *flags*, no notification
>>> @@ -4083,9 +4083,9 @@ union bpf_attr {
>>> *            If **BPF_RB_FORCE_WAKEUP** is specified in *flags*, notification
>>> *            of new data availability is sent unconditionally.
>>> *    Return
>>> - *           Nothing. Always succeeds.
>>> + *           0 on success, or a negative error in case of failure.
>>> *
>>> - * void bpf_ringbuf_discard(void *data, u64 flags)
>>> + * int bpf_ringbuf_discard(void *data, u64 flags)
>> 
>> Ditto. And same for tools/include/uapi/linux/bpf.h
>> 
>>> *    Description
>>> *            Discard reserved ring buffer sample, pointed to by *data*.
>>> *            If **BPF_RB_NO_WAKEUP** is specified in *flags*, no notification
>>> @@ -4095,7 +4095,7 @@ union bpf_attr {
>>> *            If **BPF_RB_FORCE_WAKEUP** is specified in *flags*, notification
>>> *            of new data availability is sent unconditionally.
>>> *    Return
>>> - *           Nothing. Always succeeds.
>>> + *           0 on success, or a negative error in case of failure.
>>> *
>>> * u64 bpf_ringbuf_query(void *ringbuf, u64 flags)
>>> *    Description
>>> diff --git a/kernel/bpf/ringbuf.c b/kernel/bpf/ringbuf.c
>>> index f25b719ac786..f76dafe2427e 100644
>>> --- a/kernel/bpf/ringbuf.c
>>> +++ b/kernel/bpf/ringbuf.c
>>> @@ -397,26 +397,35 @@ static void bpf_ringbuf_commit(void *sample, u64 flags, bool discard)
>>> 
>>> BPF_CALL_2(bpf_ringbuf_submit, void *, sample, u64, flags)
>>> {
>>> +     if (unlikely(flags & ~(BPF_RB_NO_WAKEUP | BPF_RB_FORCE_WAKEUP)))
>>> +             return -EINVAL;
>> 
>> We can move this check to bpf_ringbuf_commit().
> 
> I don't believe we can because in 'bpf_ringbuf_output()' the flag
> checking in 'bpf_ringbuf_commit()' is already
> too late.

I see. Let's keep it in current functions then. 

Thanks,
Song