Re: [PATCH 05/11] perf parse-event: Fix memory leak in evsel->unit

Arnaldo Carvalho de Melo
2020-09-15T20:06:12Z

Em Tue, Sep 15, 2020 at 11:59:13AM -0700, Ian Rogers escreveu:
> On Tue, Sep 15, 2020 at 5:19 AM Arnaldo Carvalho de Melo
> <acme@kernel.org> wrote:
> >
> > Em Tue, Sep 15, 2020 at 12:18:13PM +0900, Namhyung Kim escreveu:
> > > The evsel->unit borrows a pointer of pmu event or alias instead of
> > > owns a string. But tool event (duration_time) passes a result of
> > > strdup() caused a leak.
> > >
> > > It was found by ASAN during metric test:
> >
> > Thanks, applied.
>
> Thanks Namhyung and Arnaldo, just to raise a meta point. A lot of the
> parse-events asan failures were caused by a lack of strdup causing
> frees of string literals. It seems we're now adding strdup defensively
> but introducing memory leaks. Could we be doing this in a smarter way?

I hope so, the parsing code was always something I thought about
auditing but never had time to work on, whatever you can do to help with
that will be great!

- Arnaldo

> For C++ I'd likely use std::string and walk away. For perf code the
> best source of "ownership" I've found is to look at the "delete"
> functions and figure out ownership from what gets freed there - this
> can be burdensome. For strings, the code is also using strbuf and
> asprintf. One possible improvement could be to document ownership next
> to the struct member variable declarations. Another idea would be to
> declare a macro whose usage would look like:
>
> struct evsel {
> ...
> OWNER(char *name, "this");
> ...
> UNOWNED(const char *unit);
> ...
>
> Maybe then we could get a static analyzer to complain if a literal
> were assigned to an owned struct variable. Perhaps if a strdup were
> assigned to an UNOWNED struct variable perhaps it could warn too, as
> presumably the memory allocation is a request to own the memory.
>
> There was a talk about GCC's -fanalyzer option doing malloc/free
> checking at Linux plumbers 2 weeks ago:
> https://linuxplumbersconf.org/event/7/contributions/721/attachments/542/961/2020-LPC-analyzer-talk.pdf
> I added David Malcolm, the LPC presenter, as he may have ideas on how
> we could do this in a better way.
>
> Thanks,
> Ian
>
>
> > > Direct leak of 210 byte(s) in 70 object(s) allocated from:
> > > #0 0x7fe366fca0b5 in strdup (/lib/x86_64-linux-gnu/libasan.so.5+0x920b5)
> > > #1 0x559fbbcc6ea3 in add_event_tool util/parse-events.c:414
> > > #2 0x559fbbcc6ea3 in parse_events_add_tool util/parse-events.c:1414
> > > #3 0x559fbbd8474d in parse_events_parse util/parse-events.y:439
> > > #4 0x559fbbcc95da in parse_events__scanner util/parse-events.c:2096
> > > #5 0x559fbbcc95da in __parse_events util/parse-events.c:2141
> > > #6 0x559fbbc28555 in check_parse_id tests/pmu-events.c:406
> > > #7 0x559fbbc28555 in check_parse_id tests/pmu-events.c:393
> > > #8 0x559fbbc28555 in check_parse_cpu tests/pmu-events.c:415
> > > #9 0x559fbbc28555 in test_parsing tests/pmu-events.c:498
> > > #10 0x559fbbc0109b in run_test tests/builtin-test.c:410
> > > #11 0x559fbbc0109b in test_and_print tests/builtin-test.c:440
> > > #12 0x559fbbc03e69 in __cmd_test tests/builtin-test.c:695
> > > #13 0x559fbbc03e69 in cmd_test tests/builtin-test.c:807
> > > #14 0x559fbbc691f4 in run_builtin /home/namhyung/project/linux/tools/perf/perf.c:312
> > > #15 0x559fbbb071a8 in handle_internal_command /home/namhyung/project/linux/tools/perf/perf.c:364
> > > #16 0x559fbbb071a8 in run_argv /home/namhyung/project/linux/tools/perf/perf.c:408
> > > #17 0x559fbbb071a8 in main /home/namhyung/project/linux/tools/perf/perf.c:538
> > > #18 0x7fe366b68cc9 in __libc_start_main ../csu/libc-start.c:308
> > >
> > > Acked-by: Jiri Olsa <jolsa@redhat.com>
> > > Fixes: f0fbb114e3025 ("perf stat: Implement duration_time as a proper event")
> > > Signed-off-by: Namhyung Kim <namhyung@kernel.org>
> > > ---
> > > tools/perf/util/parse-events.c | 2 +-
> > > 1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/tools/perf/util/parse-events.c b/tools/perf/util/parse-events.c
> > > index b35e4bb1cecb..ece321ccf599 100644
> > > --- a/tools/perf/util/parse-events.c
> > > +++ b/tools/perf/util/parse-events.c
> > > @@ -416,7 +416,7 @@ static int add_event_tool(struct list_head *list, int *idx,
> > > return -ENOMEM;
> > > evsel->tool_event = tool_event;
> > > if (tool_event == PERF_TOOL_DURATION_TIME)
> > > - evsel->unit = strdup("ns");
> > > + evsel->unit = "ns";
> > > return 0;
> > > }
> > >
> > > --
> > > 2.28.0.618.gf4bc123cb7-goog
> > >
> >
> > --
> >
> > - Arnaldo

--

- Arnaldo