Re: [PATCH 1/2] perf script: Initialize buffer for regs_map()

[Ian Rogers]

On Thu, Jun 22, 2023 at 4:54 PM Namhyung Kim <namhyung@xxxxxxxxxx> wrote:
>
> The buffer is used to save register mapping in a sample.  Normally
> perf samples don't have any register so the string should be empty.
> But it missed to initialize the buffer when the size is 0.  And it's
> passed to PyUnicode_FromString() with a garbage data.
>
> So it returns NULL due to invalid input (instead of an empty unicode
> string object) which causes a segfault like below:
>
>   Thread 2.1 "perf" received signal SIGSEGV, Segmentation fault.
>   [Switching to Thread 0x7ffff7c83780 (LWP 193775)]
>   0x00007ffff6dbca2e in PyDict_SetItem () from /lib/x86_64-linux-gnu/libpython3.11.so.1.0
>   (gdb) bt
>   #0  0x00007ffff6dbca2e in PyDict_SetItem () from /lib/x86_64-linux-gnu/libpython3.11.so.1.0
>   #1  0x00007ffff6dbf848 in PyDict_SetItemString () from /lib/x86_64-linux-gnu/libpython3.11.so.1.0
>   #2  0x000055555575824d in pydict_set_item_string_decref (val=0x0, key=0x5555557f96e3 "iregs", dict=0x7ffff5f7f780)
>       at util/scripting-engines/trace-event-python.c:145
>   #3  set_regs_in_dict (evsel=0x555555efc370, sample=0x7fffffffb870, dict=0x7ffff5f7f780)
>       at util/scripting-engines/trace-event-python.c:776
>   #4  get_perf_sample_dict (sample=sample@entry=0x7fffffffb870, evsel=evsel@entry=0x555555efc370, al=al@entry=0x7fffffffb2e0,
>       addr_al=addr_al@entry=0x0, callchain=callchain@entry=0x7ffff63ef440) at util/scripting-engines/trace-event-python.c:923
>   #5  0x0000555555758ec1 in python_process_tracepoint (sample=0x7fffffffb870, evsel=0x555555efc370, al=0x7fffffffb2e0, addr_al=0x0)
>       at util/scripting-engines/trace-event-python.c:1044
>   #6  0x00005555555c5db8 in process_sample_event (tool=<optimized out>, event=<optimized out>, sample=<optimized out>,
>       evsel=0x555555efc370, machine=0x555555ef4d68) at builtin-script.c:2421
>   #7  0x00005555556b7793 in perf_session__deliver_event (session=0x555555ef4b60, event=0x7ffff62ff7d0, tool=0x7fffffffc150,
>       file_offset=30672, file_path=0x555555efb8a0 "perf.data") at util/session.c:1639
>   #8  0x00005555556bc864 in do_flush (show_progress=true, oe=0x555555efb700) at util/ordered-events.c:245
>   #9  __ordered_events__flush (oe=oe@entry=0x555555efb700, how=how@entry=OE_FLUSH__FINAL, timestamp=timestamp@entry=0)
>       at util/ordered-events.c:324
>   #10 0x00005555556bd06e in ordered_events__flush (oe=oe@entry=0x555555efb700, how=how@entry=OE_FLUSH__FINAL)
>       at util/ordered-events.c:342
>   #11 0x00005555556b9d63 in __perf_session__process_events (session=0x555555ef4b60) at util/session.c:2465
>   #12 perf_session__process_events (session=0x555555ef4b60) at util/session.c:2627
>   #13 0x00005555555cb1d0 in __cmd_script (script=0x7fffffffc150) at builtin-script.c:2839
>   #14 cmd_script (argc=<optimized out>, argv=<optimized out>) at builtin-script.c:4365
>   #15 0x0000555555650811 in run_builtin (p=p@entry=0x555555ed8948 <commands+456>, argc=argc@entry=4, argv=argv@entry=0x7fffffffe240)
>       at perf.c:323
>   #16 0x0000555555597eb3 in handle_internal_command (argv=0x7fffffffe240, argc=4) at perf.c:377
>   #17 run_argv (argv=<synthetic pointer>, argcp=<synthetic pointer>) at perf.c:421
>   #18 main (argc=4, argv=0x7fffffffe240) at perf.c:537
>
> Fixes: 51cfe7a3e87e ("perf python: Avoid 2 leak sanitizer issues")
> Signed-off-by: Namhyung Kim <namhyung@xxxxxxxxxx>

Acked-by: Ian Rogers <irogers@xxxxxxxxxx>

Thanks,
Ian

> ---
>  tools/perf/util/scripting-engines/trace-event-python.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/tools/perf/util/scripting-engines/trace-event-python.c b/tools/perf/util/scripting-engines/trace-event-python.c
> index 25fcd6630a4d..94312741443a 100644
> --- a/tools/perf/util/scripting-engines/trace-event-python.c
> +++ b/tools/perf/util/scripting-engines/trace-event-python.c
> @@ -737,11 +737,11 @@ static void regs_map(struct regs_dump *regs, uint64_t mask, const char *arch, ch
>         unsigned int i = 0, r;
>         int printed = 0;
>
> +       bf[0] = 0;
> +
>         if (size <= 0)
>                 return;
>
> -       bf[0] = 0;
> -
>         if (!regs || !regs->regs)
>                 return;
>
> --
> 2.41.0.162.gfafddb0af9-goog
>