Re: [PATCH, Libbacktrace] Fix possible SEGV when handling stripped PIE binaries.

[Ian Lance Taylor <iant at google dot com>]

On Wed, Mar 2, 2016 at 6:21 AM, Maxim Ostapenko
<m.ostapenko@partner.samsung.com> wrote:
> On 02/03/16 16:59, Ian Lance Taylor wrote:
>>
>> On Wed, Mar 2, 2016 at 12:51 AM, Maxim Ostapenko
>> <m.ostapenko@partner.samsung.com> wrote:
>>>
>>> When testing ASan on large system, I've noticed that sometimes it crashes
>>> with SEGV in Libbacktrace when trying to symbolize stripped PIE (compiled
>>> with -pie -fPIC) binaries in fully stripped environment (this means that
>>> all
>>> dependent libraries are also stripped). Here a scenario I've observed:
>>>
>>> 1) _asan_backtrace_initialize calls elf_add passing &elf_fileline_fn as
>>> output parameter to properly initialize it.
>>> 2) elf_add doesn't elf_fileline_fn initialize and returns -1 for stripped
>>> PIE binary.
>>> 3) _asan_backtrace_initialize calls phdr_callback on each dependent
>>> library
>>> via dl_iterate_phdr.
>>> 4) phdr_callback initializes elf_fileline_fn iff it found debug info in
>>> some
>>> library (found_dwarf == 1), but this is false since all libs are
>>> stripped.
>>> So, we still have uninitialized elf_fileline_fn value.
>>> 5) _asan_backtrace_initialize uses elf_fileline_fn to initialize proper
>>> fileline_fn callback.
>>> 6) Libbacktrace uses fileline_fn callback later and crashes because it
>>> contains garbage.
>>>
>>> This patch fixes the issue by simply initializing elf_fileline_fn via
>>> elf_nodebug in _asan_backtrace_initialize prologue.
>>>
>>> Tested on x86_64-linux-gnu and arm-linux-gnueabi, OK for trunk?
>>
>> Thanks for the analysis.  I would rather set *fileline_fn in the case
>> where elf_add returns -1.  Or, remove the setting of *fileline_fn =
>> elf_nodebug in elf_add, since that would become the default.
>>
>> Ian
>>
>
> Thanks, does this look better (I used the second option)?

This is OK with a ChangeLog entry.  Thanks.

Ian