netdev - RE: [PATCH bpf 1/2] bpf: bpf_probe_read_kernel_str() has to return amount of data read on success

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Message-ID: <5ee86e42810c7_4be02ab1b668a5b430@john-XPS-13-9370.notmuch>
Date:   Tue, 16 Jun 2020 00:01:22 -0700
From:   John Fastabend <john.fastabend@...il.com>
To:     Andrii Nakryiko <andriin@...com>, bpf@...r.kernel.org,
        netdev@...r.kernel.org, ast@...com, daniel@...earbox.net
Cc:     andrii.nakryiko@...il.com, kernel-team@...com,
        Andrii Nakryiko <andriin@...com>,
        Christoph Hellwig <hch@....de>
Subject: RE: [PATCH bpf 1/2] bpf: bpf_probe_read_kernel_str() has to return
 amount of data read on success

Andrii Nakryiko wrote:
> During recent refactorings, bpf_probe_read_kernel_str() started returning 0 on
> success, instead of amount of data successfully read. This majorly breaks
> applications relying on bpf_probe_read_kernel_str() and bpf_probe_read_str()
> and their results. Fix this by returning actual number of bytes read.
> 
> Cc: Christoph Hellwig <hch@....de>
> Fixes: 8d92db5c04d1 ("bpf: rework the compat kernel probe handling")
> Signed-off-by: Andrii Nakryiko <andriin@...com>
> ---
>  kernel/trace/bpf_trace.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index e729c9e587a0..a3ac7de98baa 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -241,7 +241,7 @@ bpf_probe_read_kernel_str_common(void *dst, u32 size, const void *unsafe_ptr)
>  	if (unlikely(ret < 0))
>  		goto fail;
>  
> -	return 0;
> +	return ret;
>  fail:
>  	memset(dst, 0, size);
>  	return ret;
> -- 
> 2.24.1
> 

Acked-by: John Fastabend <john.fastabend@...il.com>