Re: [PATCH] perf symbols: Fix return incorrect build_id size in elf_read_build_id()

[Adrian Hunter <adrian.hunter@intel.com>]

On 27/04/23 04:28, Yang Jihong wrote:
> In elf_read_build_id(), if gnu build_id is found, should return the size of
> the actually copied data. If descsz is greater thanBuild_ID_SIZE,
> write_buildid data access may occur.
> 
> Fixes: be96ea8ffa78 ("perf symbols: Fix issue with binaries using 16-bytes buildids (v2)")
> Reported-by: Will Ochowicz <Will.Ochowicz@genusplc.com>
> Link: https://lore.kernel.org/lkml/CWLP265MB49702F7BA3D6D8F13E4B1A719C649@CWLP265MB4970.GBRP265.PROD.OUTLOOK.COM/T/
> Tested-by: Will Ochowicz <Will.Ochowicz@genusplc.com>
> Signed-off-by: Yang Jihong <yangjihong1@huawei.com>

As an aside, note that the build ID on the ELF file triggering the bug was
62363266373430613439613534633666326432323334653665623530396566343938656130663039
which is 80 ASCII characters, which would have been a 20 byte binary number i.e.

$ echo -en "0000: 62363266373430613439613534633666\n0010: 32643232333465366562353039656634\n0020: 3938656130663039" | xxd -r | od -c -A d 
0000000   b   6   2   f   7   4   0   a   4   9   a   5   4   c   6   f
0000016   2   d   2   2   3   4   e   6   e   b   5   0   9   e   f   4
0000032   9   8   e   a   0   f   0   9
0000040

So perhaps a mistake in the creation of the build ID on that ELF file.

In any case, for the fix:

Acked-by: Adrian Hunter <adrian.hunter@intel.com>

> ---
>  tools/perf/util/symbol-elf.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
> index 41882ae8452e..059f88eca630 100644
> --- a/tools/perf/util/symbol-elf.c
> +++ b/tools/perf/util/symbol-elf.c
> @@ -903,7 +903,7 @@ static int elf_read_build_id(Elf *elf, void *bf, size_t size)
>  				size_t sz = min(size, descsz);
>  				memcpy(bf, ptr, sz);
>  				memset(bf + sz, 0, size - sz);
> -				err = descsz;
> +				err = sz;
>  				break;
>  			}
>  		}