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

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Date:   Mon, 29 Mar 2021 16:10:46 +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 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(). 

Thanks,
Song

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