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

[Jiri Olsa]

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@xxxxxxxxxx>
> ---
>  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 ;-)

thanks,
jirka

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