netdev - Re: [PATCH v2 3/4] libbpf: require size hint in bpf_prog_test

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Date:   Tue, 20 Nov 2018 11:18:10 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Lorenz Bauer <lmb@...udflare.com>
Cc:     ast@...nel.org, daniel@...earbox.net, netdev@...r.kernel.org,
        linux-api@...r.kernel.org, ys114321@...il.com
Subject: Re: [PATCH v2 3/4] libbpf: require size hint in bpf_prog_test_run

On Tue, Nov 20, 2018 at 03:43:05PM +0000, Lorenz Bauer wrote:
> Require size_out to be non-NULL if data_out is given. This prevents
> accidental overwriting of process memory after the output buffer.
> 
> Adjust callers of bpf_prog_test_run to this behaviour.
> 
> Signed-off-by: Lorenz Bauer <lmb@...udflare.com>
> ---
>  tools/lib/bpf/bpf.c                      |  7 ++++++-
>  tools/testing/selftests/bpf/test_progs.c | 10 ++++++++++
>  2 files changed, 16 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
> index 961e1b9fc592..1a835ff27486 100644
> --- a/tools/lib/bpf/bpf.c
> +++ b/tools/lib/bpf/bpf.c
> @@ -407,15 +407,20 @@ int bpf_prog_test_run(int prog_fd, int repeat, void *data, __u32 size,
>  	union bpf_attr attr;
>  	int ret;
>  
> +	if (data_out && !size_out)
> +		return -EINVAL;
> +
>  	bzero(&attr, sizeof(attr));
>  	attr.test.prog_fd = prog_fd;
>  	attr.test.data_in = ptr_to_u64(data);
>  	attr.test.data_out = ptr_to_u64(data_out);
>  	attr.test.data_size_in = size;
> +	if (data_out)
> +		attr.test.data_size_out = *size_out;
>  	attr.test.repeat = repeat;
>  
>  	ret = sys_bpf(BPF_PROG_TEST_RUN, &attr, sizeof(attr));
> -	if (size_out)
> +	if (data_out)
>  		*size_out = attr.test.data_size_out;
>  	if (retval)
>  		*retval = attr.test.retval;
> diff --git a/tools/testing/selftests/bpf/test_progs.c b/tools/testing/selftests/bpf/test_progs.c
> index c1e688f61061..299938603cb6 100644
> --- a/tools/testing/selftests/bpf/test_progs.c
> +++ b/tools/testing/selftests/bpf/test_progs.c
> @@ -150,6 +150,7 @@ static void test_xdp(void)
>  	bpf_map_update_elem(map_fd, &key4, &value4, 0);
>  	bpf_map_update_elem(map_fd, &key6, &value6, 0);
>  
> +	size = sizeof(buf);
>  	err = bpf_prog_test_run(prog_fd, 1, &pkt_v4, sizeof(pkt_v4),
>  				buf, &size, &retval, &duration);
>  
> @@ -158,6 +159,7 @@ static void test_xdp(void)
>  	      "err %d errno %d retval %d size %d\n",
>  	      err, errno, retval, size);
>  
> +	size = sizeof(buf);
>  	err = bpf_prog_test_run(prog_fd, 1, &pkt_v6, sizeof(pkt_v6),
>  				buf, &size, &retval, &duration);

This will surely break existing bpf_prog_test_run users.
Like it will break our testing framework.
we can fix out stuff and libbpf is a user space library, but I don't
think that this is the case to invoke such pain.
libbpf's bpf_prog_test_run() should be a simple wrapper on top of syscall.
I don't think it should be making such restrictions on api.

btw patch 1 looks good to me.