[PATCH] perf record: Fix a segfault in record__read_lost_samples()

[Namhyung Kim]

When it fails to open events record__open() returns without setting the
session->evlist.  Then it gets a segfault in the function trying to read
lost sample counts.  You can easily reproduce it as a normal user like:

  $ perf record -p 1 true
  ...
  perf: Segmentation fault
  ...

Skip the function if it has no evlist.  And add more protection for evsels
which are not properly initialized.

Signed-off-by: Namhyung Kim <namhyung@xxxxxxxxxx>
---
I didn't add a Fixes tag as it's not sent to Linus yet.
But in case you want it.

  Fixes: a49aa8a54e86 ("perf record: Read and inject LOST_SAMPLES events")

 tools/perf/builtin-record.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index 9df77b81a3bb..fe34d5db23bd 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -1888,6 +1888,10 @@ static void record__read_lost_samples(struct record *rec)
 	struct perf_record_lost_samples *lost;
 	struct evsel *evsel;
 
+	/* there was an error during record__open */
+	if (session->evlist == NULL)
+		return;
+
 	lost = zalloc(PERF_SAMPLE_MAX_SIZE);
 	if (lost == NULL) {
 		pr_debug("Memory allocation failed\n");
@@ -1899,6 +1903,8 @@ static void record__read_lost_samples(struct record *rec)
 	evlist__for_each_entry(session->evlist, evsel) {
 		struct xyarray *xy = evsel->core.sample_id;
 
+		if (xy == NULL || evsel->core.fd == NULL)
+			continue;
 		if (xyarray__max_x(evsel->core.fd) != xyarray__max_x(xy) ||
 		    xyarray__max_y(evsel->core.fd) != xyarray__max_y(xy)) {
 			pr_debug("Unmatched FD vs. sample ID: skip reading LOST count\n");
-- 
2.37.2.789.g6183377224-goog