[PATCH] perf hist: Update hist symbol when updating maps

[Matt Fleming <matt@readmodwrite.com>]

AddressSanitizer found a use-after-free bug in the symbol code which
manifested as perf top segfaulting.

  ==1238389==ERROR: AddressSanitizer: heap-use-after-free on address 0x60b00c48844b at pc 0x5650d8035961 bp 0x7f751aaecc90 sp 0x7f751aaecc80
  READ of size 1 at 0x60b00c48844b thread T193
      #0 0x5650d8035960 in _sort__sym_cmp util/sort.c:310
      #1 0x5650d8043744 in hist_entry__cmp util/hist.c:1286
      #2 0x5650d8043951 in hists__findnew_entry util/hist.c:614
      #3 0x5650d804568f in __hists__add_entry util/hist.c:754
      #4 0x5650d8045bf9 in hists__add_entry util/hist.c:772
      #5 0x5650d8045df1 in iter_add_single_normal_entry util/hist.c:997
      #6 0x5650d8043326 in hist_entry_iter__add util/hist.c:1242
      #7 0x5650d7ceeefe in perf_event__process_sample /home/matt/src/linux/tools/perf/builtin-top.c:845
      #8 0x5650d7ceeefe in deliver_event /home/matt/src/linux/tools/perf/builtin-top.c:1208
      #9 0x5650d7fdb51b in do_flush util/ordered-events.c:245
      #10 0x5650d7fdb51b in __ordered_events__flush util/ordered-events.c:324
      #11 0x5650d7ced743 in process_thread /home/matt/src/linux/tools/perf/builtin-top.c:1120
      #12 0x7f757ef1f133 in start_thread nptl/pthread_create.c:442
      #13 0x7f757ef9f7db in clone3 ../sysdeps/unix/sysv/linux/x86_64/clone3.S:81

When updating hist maps it's also necessary to update the hist symbol
reference because the old one gets freed in map__put().

While this bug was probably introduced with 5c24b67aae72 ("perf tools:
Replace map->referenced & maps->removed_maps with map->refcnt"), the
symbol objects were leaked until c087e9480cf3 ("perf machine: Fix
refcount usage when processing PERF_RECORD_KSYMBOL") was merged so the
bug was masked.

Fixes: c087e9480cf3 ("perf machine: Fix refcount usage when processing PERF_RECORD_KSYMBOL")
Signed-off-by: Matt Fleming (Cloudflare) <matt@readmodwrite.com>
Reported-by: Yunzhao Li <yunzhao@cloudflare.com>
Cc: stable@vger.kernel.org # v5.13+
---
 tools/perf/util/hist.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/tools/perf/util/hist.c b/tools/perf/util/hist.c
index 0f554febf9a1..0f9ce2ee2c31 100644
--- a/tools/perf/util/hist.c
+++ b/tools/perf/util/hist.c
@@ -639,6 +639,11 @@ static struct hist_entry *hists__findnew_entry(struct hists *hists,
 			 * the history counter to increment.
 			 */
 			if (he->ms.map != entry->ms.map) {
+				if (he->ms.sym) {
+					u64 addr = he->ms.sym->start;
+					he->ms.sym = map__find_symbol(entry->ms.map, addr);
+				}
+
 				map__put(he->ms.map);
 				he->ms.map = map__get(entry->ms.map);
 			}
-- 
2.34.1