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Subject: Re: [PATCH] bpftool: Fix prog dump by tag
To:     Jiri Olsa <jolsa@kernel.org>, Alexei Starovoitov <ast@kernel.org>
Cc:     lkml <linux-kernel@vger.kernel.org>, netdev@vger.kernel.org,
        Lance Digby <ldigby@redhat.com>
References: <20190118125817.10763-1-jolsa@kernel.org>
From:   Daniel Borkmann <daniel@iogearbox.net>
Message-ID: <182563c3-8e11-d489-2e9e-68a391e63f3e@iogearbox.net>
Date:   Wed, 23 Jan 2019 09:58:22 +0100
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On 01/18/2019 01:58 PM, Jiri Olsa wrote:
> Lance reported an issue with bpftool not being able to
> dump program if there are more programs loaded and you
> want to dump any but the first program, like:
> 
>   # bpftool prog
>   28: kprobe  name trace_req_start  tag 1dfc28ba8b3dd597  gpl
>   	loaded_at 2019-01-18T17:02:40+1100  uid 0
>   	xlated 112B  jited 109B  memlock 4096B  map_ids 13
>   29: kprobe  name trace_req_compl  tag 5b6a5ecc6030a683  gpl
>   	loaded_at 2019-01-18T17:02:40+1100  uid 0
>   	xlated 928B  jited 575B  memlock 4096B  map_ids 13,14
>   #  bpftool prog dum jited tag 1dfc28ba8b3dd597
>    0:	push   %rbp
>    1:	mov    %rsp,%rbp
>   ...
> 
>   #  bpftool prog dum jited tag 5b6a5ecc6030a683
>   Error: can't get prog info (29): Bad address
> 
> The problem is in the prog_fd_by_tag function not cleaning
> the struct bpf_prog_info before another request, so the
> previous program length is still in there and kernel assumes
> it needs to dump the program, which fails because there's no
> user pointer set.
> 
> Moving the struct bpf_prog_info declaration into the loop,
> so it gets cleaned before each query.
> 
> Reported-by: Lance Digby <ldigby@redhat.com>
> Signed-off-by: Jiri Olsa <jolsa@kernel.org>

Applied to bpf and added Fixes tags, thanks!