[PATCH] perf machine: Fix NULL deref in thread__resolve_callchain_sample()

[lv.yating]

From: lvyating <lv.yating@xxxxxxxxxx>

When recording with -j stack, resolve_lbr_callchain_sample() can
dereference a NULL 'chain' pointer while resolving the branch
stack.

$ perf record -j stack -e branches:u uname
perf: Segmentation fault

Fix it by checking 'chain' for NULL before dereferencing it.

Fixes: 29be60c93d2d ("perf build-id: Mark DSO in sample callchains")
Signed-off-by: lvyating <lv.yating@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
---
 tools/perf/util/machine.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
index f86b3b7df742..10a88c070814 100644
--- a/tools/perf/util/machine.c
+++ b/tools/perf/util/machine.c
@@ -2858,7 +2858,7 @@ static int thread__resolve_callchain_sample(struct thread *thread,
 	if (chain)
 		chain_nr = chain->nr;

-	if (evsel__has_branch_callstack(evsel)) {
+	if (chain && evsel__has_branch_callstack(evsel)) {
 		struct perf_env *env = evsel__env(evsel);

 		err = resolve_lbr_callchain_sample(thread, cursor, sample, parent,
-- 
2.27.0