Re: [PATCH] perf synthetic events: Avoid write of uninitialized memory.

Jiri Olsa
2021-03-10T11:49:28Z

On Tue, Mar 09, 2021 at 03:49:45PM -0800, Ian Rogers wrote:
> Account for alignment bytes in the zero-ing memset.
>
> Signed-off-by: Ian Rogers <irogers@google.com>
> ---
> tools/perf/util/synthetic-events.c | 9 +++++----
> 1 file changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/tools/perf/util/synthetic-events.c b/tools/perf/util/synthetic-events.c
> index b698046ec2db..31bf3dd6a1e0 100644
> --- a/tools/perf/util/synthetic-events.c
> +++ b/tools/perf/util/synthetic-events.c
> @@ -424,7 +424,7 @@ int perf_event__synthesize_mmap_events(struct perf_tool *tool,
>
> while (!io.eof) {
> static const char anonstr[] = "//anon";
> - size_t size;
> + size_t size, aligned_size;
>
> /* ensure null termination since stack will be reused. */
> event->mmap2.filename[0] = '\0';
> @@ -484,11 +484,12 @@ int perf_event__synthesize_mmap_events(struct perf_tool *tool,
> }
>
> size = strlen(event->mmap2.filename) + 1;
> - size = PERF_ALIGN(size, sizeof(u64));
> + aligned_size = PERF_ALIGN(size, sizeof(u64));
> event->mmap2.len -= event->mmap.start;
> event->mmap2.header.size = (sizeof(event->mmap2) -
> - (sizeof(event->mmap2.filename) - size));
> - memset(event->mmap2.filename + size, 0, machine->id_hdr_size);
> + (sizeof(event->mmap2.filename) - aligned_size));
> + memset(event->mmap2.filename + size, 0, machine->id_hdr_size +
> + (aligned_size - size));

so we did not zero the extra alignment bytes, nice ;-) looks good

Acked-by: Jiri Olsa <jolsa@redhat.com>

thanks,
jirka

> event->mmap2.header.size += machine->id_hdr_size;
> event->mmap2.pid = tgid;
> event->mmap2.tid = pid;
> --
> 2.30.1.766.gb4fecdf3b7-goog
>