Re: [PATCH] bpftool: Fix prog dump by tag

[Jakub Kicinski]

On Fri, 18 Jan 2019 13:58:17 +0100, 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@xxxxxxxxxx>
> Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>

Aw.

Acked-by: Jakub Kicinski <jakub.kicinski@xxxxxxxxxxxxx>

Thanks!