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

[Jiri Olsa <jolsa@redhat.com>]

On Sat, Mar 14, 2020 at 09:49:37AM -0700, Ian Rogers wrote:
> 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.

I was wondering if we should fail completely,
but we might break some c2c expected behaviour

how about just WARN_ONCE pn j == 0, and then
the lookup will fail already with:

        if (WARN_ONCE(node < 0, "WARNING: failed to find node\n"))
                return;

just get enough hints ;-)

jirka

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