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

[Yang Jihong]

Hello,

On 2023/4/27 14:02, Adrian Hunter wrote:
> 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@xxxxxxxxxxxx>
> > Link: https://lore.kernel.org/lkml/CWLP265MB49702F7BA3D6D8F13E4B1A719C649@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/T/
> > Tested-by: Will Ochowicz <Will.Ochowicz@xxxxxxxxxxxx>
> > Signed-off-by: Yang Jihong <yangjihong1@xxxxxxxxxx>
>
> 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.
Yes, it may be an error, or it may be that the build-id was specified 
when the elf file was created.

I tried ld can specify a build-id larger than 160-bit hexadecimal digits:

  $ ld -o test test.o 
--build-id=0x62363266373430613439613534633666326432323334653665623530396566343938656130663039
  $ readelf -n test

  Displaying notes found in: .note.gnu.build-id
    Owner                 Data size       Description
    GNU                  0x00000028       NT_GNU_BUILD_ID (unique build 
ID bitstring)
      Build ID: 
62363266373430613439613534633666326432323334653665623530396566343938656130663039

All in all, it feels like a rare scene :)

> In any case, for the fix:
>
> Acked-by: Adrian Hunter <adrian.hunter@xxxxxxxxx>
Thanks for the acked-by.

Thanks,
Yang