Re: [PATCH v2] perf record: Fix coredump with --overwrite and --max-size

[Namhyung Kim]

Hello,

On Wed, Jan 4, 2023 at 8:09 PM Yang Jihong <yangjihong1@xxxxxxxxxx> wrote:
>
> Hello,
>
> On 2023/1/4 0:50, Namhyung Kim wrote:
> > On Mon, Jan 2, 2023 at 8:20 AM Arnaldo Carvalho de Melo <acme@xxxxxxxxxx> wrote:
> >>
> >> Em Thu, Dec 29, 2022 at 12:47:28PM +0000, Yang Jihong escreveu:
> >>> When --overwrite and --max-size options of perf record are used together,
> >>> a segmentation fault occurs. The following is an example:
> >>>
> >>>   # perf record -e sched:sched* --overwrite --max-size 1M -a -- sleep 1
> >>>    [ perf record: Woken up 1 times to write data ]
> >>>    perf: Segmentation fault
> >>>    Obtained 1 stack frames.
> >>>    [0xc4c67f]
> >>>    Segmentation fault (core dumped)
> >>>
> >>> backtrace of the core file is as follows:
> >>>
> >>>    #0  0x0000000000417990 in process_locked_synthesized_event (tool=0x0, event=0x15, sample=0x1de0, machine=0xf8) at builtin-record.c:630
> >>>    #1  0x000000000057ee53 in perf_event__synthesize_threads (nr_threads_synthesize=21, mmap_data=<optimized out>, needs_mmap=<optimized out>, machine=0x17ad9b0, process=<optimized out>, tool=0x0) at util/synthetic-events.c:1950
> >>>    #2  __machine__synthesize_threads (nr_threads_synthesize=0, data_mmap=<optimized out>, needs_mmap=<optimized out>, process=<optimized out>, threads=0x8, target=0x8, tool=0x0, machine=0x17ad9b0) at util/synthetic-events.c:1936
> >>>    #3  machine__synthesize_threads (machine=0x17ad9b0, target=0x8, threads=0x8, needs_mmap=<optimized out>, data_mmap=<optimized out>, nr_threads_synthesize=0) at util/synthetic-events.c:1947
> >>>    #4  0x000000000040165d in record__synthesize (tail=<optimized out>, rec=0xbe2520 <record>) at builtin-record.c:2010
> >>>    #5  0x0000000000403989 in __cmd_record (argc=<optimized out>, argv=<optimized out>, rec=0xbe2520 <record>) at builtin-record.c:2810
> >>>    #6  0x00000000004196ba in record__init_thread_user_masks (rec=0xbe2520 <record>, cpus=0x17a65f0) at builtin-record.c:3837
> >>>    #7  record__init_thread_masks (rec=0xbe2520 <record>) at builtin-record.c:3938
> >>>    #8  cmd_record (argc=1, argv=0x7ffdd692dc60) at builtin-record.c:4241
> >>>    #9  0x00000000004b701d in pager_command_config (var=0x0, value=0x15 <error: Cannot access memory at address 0x15>, data=0x1de0) at perf.c:117
> >>>    #10 0x00000000004b732b in get_leaf_frame_caller_aarch64 (sample=0xfffffffb, thread=0x0, usr_idx=<optimized out>) at util/arm64-frame-pointer-unwind-support.c:56
> >>>    #11 0x0000000000406331 in execv_dashed_external (argv=0x7ffdd692d9e8) at perf.c:410
> >>>    #12 run_argv (argcp=<synthetic pointer>, argv=<synthetic pointer>) at perf.c:431
> >>>    #13 main (argc=<optimized out>, argv=0x7ffdd692d9e8) at perf.c:562
> >>>
> >>> The reason is that record__bytes_written accesses the freed memory rec->thread_data,
> >>> The process is as follows:
> >>>    __cmd_record
> >>>      -> record__free_thread_data
> >>>        -> zfree(&rec->thread_data)         // free rec->thread_data
> >>>      -> record__synthesize
> >>>        -> perf_event__synthesize_id_index
> >>>          -> process_synthesized_event
> >>>            -> record__write
> >>>              -> record__bytes_written     // access rec->thread_data
> >>>
> >>> we only need to check the value of done first.
> >>> Also add variable check in record__bytes_written for code hardening,
> >>> and save bytes_written separately to reduce one calculation.
> >>>
> >>> Fixes: 6d57581659f7 ("perf record: Add support for limit perf output file size")
> >>> Signed-off-by: Yang Jihong <yangjihong1@xxxxxxxxxx>
> >>> ---
> >>>
> >>> Changes since v1:
> >>>   - Add variable check in record__bytes_written for code hardening.
> >>>   - Save bytes_written separately to reduce one calculation.
> >>>   - Remove rec->opts.tail_synthesize check.
> >>
> >> Namhyung, are you ok with this now?
> >>
> >> - Arnaldo
> >>
> >>>   tools/perf/builtin-record.c | 26 +++++++++++++++++---------
> >>>   1 file changed, 17 insertions(+), 9 deletions(-)
> >>>
> >>> diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
> >>> index 29dcd454b8e2..acba9e43e519 100644
> >>> --- a/tools/perf/builtin-record.c
> >>> +++ b/tools/perf/builtin-record.c
> >>> @@ -230,16 +230,29 @@ static u64 record__bytes_written(struct record *rec)
> >>>        u64 bytes_written = rec->bytes_written;
> >>>        struct record_thread *thread_data = rec->thread_data;
> >>>
> >>> +     if (thread_data == NULL)
> >>> +             return bytes_written;
> >>> +
> >
> > Then it won't count bytes written by threads, right?
> > I think it needs to be saved somewhere.
> >
> I'm not sure here. Can you explain it more clearly, thanks :)
> I can modify it accordingly.
>
> I think if thread_data == NULL, it is not thread data.
> In this case, we just return rec->bytes_written.

It can be thread data but freed before tail synthesis, right?
In that case, I think it needs to add bytes_written by threads
to calculate the correct data size.

Thanks,
Namhyung