Re: [PATCH] perf mem2node: avoid double free related to realloc

[Ian Rogers <irogers@google.com>]

On Sat, Mar 14, 2020 at 7:23 AM Jiri Olsa <jolsa@redhat.com> wrote:
>
> On Fri, Mar 13, 2020 at 09:28:26PM -0700, Ian Rogers wrote:
> > Realloc of size zero is a free not an error, avoid this causing a double
> > free. Caught by clang's address sanitizer:
> >
> > ==2634==ERROR: AddressSanitizer: attempting double-free on 0x6020000015f0 in thread T0:
> >     #0 0x5649659297fd in free llvm/llvm-project/compiler-rt/lib/asan/asan_malloc_linux.cpp:123:3
> >     #1 0x5649659e9251 in __zfree tools/lib/zalloc.c:13:2
> >     #2 0x564965c0f92c in mem2node__exit tools/perf/util/mem2node.c:114:2
> >     #3 0x564965a08b4c in perf_c2c__report tools/perf/builtin-c2c.c:2867:2
> >     #4 0x564965a0616a in cmd_c2c tools/perf/builtin-c2c.c:2989:10
> >     #5 0x564965944348 in run_builtin tools/perf/perf.c:312:11
> >     #6 0x564965943235 in handle_internal_command tools/perf/perf.c:364:8
> >     #7 0x5649659440c4 in run_argv tools/perf/perf.c:408:2
> >     #8 0x564965942e41 in main tools/perf/perf.c:538:3
> >
> > 0x6020000015f0 is located 0 bytes inside of 1-byte region [0x6020000015f0,0x6020000015f1)
> > freed by thread T0 here:
> >     #0 0x564965929da3 in realloc third_party/llvm/llvm-project/compiler-rt/lib/asan/asan_malloc_linux.cpp:164:3
> >     #1 0x564965c0f55e in mem2node__init tools/perf/util/mem2node.c:97:16
> >     #2 0x564965a08956 in perf_c2c__report tools/perf/builtin-c2c.c:2803:8
> >     #3 0x564965a0616a in cmd_c2c tools/perf/builtin-c2c.c:2989:10
> >     #4 0x564965944348 in run_builtin tools/perf/perf.c:312:11
> >     #5 0x564965943235 in handle_internal_command tools/perf/perf.c:364:8
> >     #6 0x5649659440c4 in run_argv tools/perf/perf.c:408:2
> >     #7 0x564965942e41 in main tools/perf/perf.c:538:3
> >
> > previously allocated by thread T0 here:
> >     #0 0x564965929c42 in calloc third_party/llvm/llvm-project/compiler-rt/lib/asan/asan_malloc_linux.cpp:154:3
> >     #1 0x5649659e9220 in zalloc tools/lib/zalloc.c:8:9
> >     #2 0x564965c0f32d in mem2node__init tools/perf/util/mem2node.c:61:12
> >     #3 0x564965a08956 in perf_c2c__report tools/perf/builtin-c2c.c:2803:8
> >     #4 0x564965a0616a in cmd_c2c tools/perf/builtin-c2c.c:2989:10
> >     #5 0x564965944348 in run_builtin tools/perf/perf.c:312:11
> >     #6 0x564965943235 in handle_internal_command tools/perf/perf.c:364:8
> >     #7 0x5649659440c4 in run_argv tools/perf/perf.c:408:2
> >     #8 0x564965942e41 in main tools/perf/perf.c:538:3
> >
> > Signed-off-by: Ian Rogers <irogers@google.com>
> > ---
> >  tools/perf/util/mem2node.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/tools/perf/util/mem2node.c b/tools/perf/util/mem2node.c
> > index 797d86a1ab09..7f97aa69eb65 100644
> > --- a/tools/perf/util/mem2node.c
> > +++ b/tools/perf/util/mem2node.c
> > @@ -95,7 +95,7 @@ int mem2node__init(struct mem2node *map, struct perf_env *env)
> >
> >       /* Cut unused entries, due to merging. */
> >       tmp_entries = realloc(entries, sizeof(*entries) * j);
> > -     if (tmp_entries)
> > +     if (j == 0 || tmp_entries)
>
> nice catch.. I wonder if we should fail in here, or at least
> warn that there're no entris.. which is really strange ;-)

The workload was the stream benchmark with perf c2c, but stream isn't
particularly long running. Not sure how j became 0, there's 2
possibilities in the code. The worry with a warning is the spam, so I
just wanted to make the code correct.

Thanks,
Ian

> thanks,
> jirka
>
> >               entries = tmp_entries;
> >
> >       for (i = 0; i < j; i++) {
> > --
> > 2.25.1.481.gfbce0eb801-goog
> >
>