[PATCH] perf ksymbol: fix memory leak: decrease refcount of map and dso

Riccardo Mancini
2021-06-02T23:16:53Z

ASan reported a memory leak of BPF-related ksymbols map and dso.
The leak is caused by refcount never reaching 0, due to missing
__put calls in the function machine__process_ksymbol_register.
Once the dso is inserted in map, dso__put should be called,
since map__new2 has increased its refcount to 2.
The same thing applies for the map when it's inserted into the
rb-tree in maps (maps__insert increases the refcount to 2).

$ sudo ./perf record -- sleep 5
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.025 MB perf.data (8 samples) ]

=================================================================
==297735==ERROR: LeakSanitizer: detected memory leaks

Direct leak of 6992 byte(s) in 19 object(s) allocated from:
#0 0x4f43c7 in calloc (/home/user/linux/tools/perf/perf+0x4f43c7)
#1 0x8e4e53 in map__new2 /home/user/linux/tools/perf/util/map.c:216:20
#2 0x8cf68c in machine__process_ksymbol_register /home/user/linux/tools/perf/util/machine.c:778:10
[...]

Indirect leak of 8702 byte(s) in 19 object(s) allocated from:
#0 0x4f43c7 in calloc (/home/user/linux/tools/perf/perf+0x4f43c7)
#1 0x8728d7 in dso__new_id /home/user/linux/tools/perf/util/dso.c:1256:20
#2 0x872015 in dso__new /home/user/linux/tools/perf/util/dso.c:1295:9
#3 0x8cf623 in machine__process_ksymbol_register /home/user/linux/tools/perf/util/machine.c:774:21
[...]

Indirect leak of 1520 byte(s) in 19 object(s) allocated from:
#0 0x4f43c7 in calloc (/home/user/linux/tools/perf/perf+0x4f43c7)
#1 0x87b3da in symbol__new /home/user/linux/tools/perf/util/symbol.c:269:23
#2 0x888954 in map__process_kallsym_symbol /home/user/linux/tools/perf/util/symbol.c:710:8
[...]

Indirect leak of 1406 byte(s) in 19 object(s) allocated from:
#0 0x4f43c7 in calloc (/home/user/linux/tools/perf/perf+0x4f43c7)
#1 0x87b3da in symbol__new /home/user/linux/tools/perf/util/symbol.c:269:23
#2 0x8cfbd8 in machine__process_ksymbol_register /home/user/linux/tools/perf/util/machine.c:803:8
[...]

Signed-off-by: Riccardo Mancini <rickyman7@gmail.com>
---
tools/perf/util/machine.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
index 3ff4936a15a42..d5937778875e1 100644
--- a/tools/perf/util/machine.c
+++ b/tools/perf/util/machine.c
@@ -776,6 +776,7 @@ static int machine__process_ksymbol_register(struct machine *machine,
if (dso) {
dso->kernel = DSO_SPACE__KERNEL;
map = map__new2(0, dso);
+ dso__put(dso);
}

if (!dso || !map) {
@@ -792,6 +793,7 @@ static int machine__process_ksymbol_register(struct machine *machine,
map->start = event->ksymbol.addr;
map->end = map->start + event->ksymbol.len;
maps__insert(&machine->kmaps, map);
+ map__put(map);
dso__set_loaded(dso);

if (is_bpf_image(event->ksymbol.name)) {
--
2.31.1