[PATCH 2/8] perf machine: Fix NULL parent dereference in fork event processing

[Arnaldo Carvalho de Melo <acme@kernel.org>]

From: Arnaldo Carvalho de Melo <acme@redhat.com>

machine__process_fork_event() calls machine__findnew_thread() for the
parent thread, which can return NULL on allocation failure.  The code
then dereferences parent via thread__pid(parent) without a NULL check
when validating whether the parent PID matches.  The later NULL check
at thread__fork() does not prevent this earlier dereference.

Add a NULL guard before accessing the parent thread.

Fixes: 5cb73340d92a ("perf tools: Make fork event processing more resilient")
Reported-by: sashiko-bot <sashiko-bot@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Assisted-by: Claude:claude-opus-4.6
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
 tools/perf/util/machine.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
index 503f5a65e0cca639..8b213482e5648e97 100644
--- a/tools/perf/util/machine.c
+++ b/tools/perf/util/machine.c
@@ -1923,7 +1923,8 @@ int machine__process_fork_event(struct machine *machine, union perf_event *event
 	 * (fork) event that would have removed the thread was lost. Assume the
 	 * latter case and continue on as best we can.
 	 */
-	if (thread__pid(parent) != (pid_t)event->fork.ppid) {
+	if (parent != NULL &&
+	    thread__pid(parent) != (pid_t)event->fork.ppid) {
 		dump_printf("removing erroneous parent thread %d/%d\n",
 			    thread__pid(parent), thread__tid(parent));
 		machine__remove_thread(machine, parent);
-- 
2.55.0