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

[Ian Rogers]

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