linux-kernel - [PATCH] perf/core: Prevent WARN_ON(!ctx) in __free

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Message-ID: <20250405203036.582721-1-gshahrouzi@gmail.com>
Date: Sat,  5 Apr 2025 16:30:36 -0400
From: Gabriel Shahrouzi <gshahrouzi@...il.com>
To: Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Jiri Olsa <jolsa@...nel.org>,
	linux-perf-users@...r.kernel.org
Cc: linux-kernel@...r.kernel.org,
	Ian Rogers <irogers@...gle.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Kan Liang <kan.liang@...ux.intel.com>,
	Shuah Khan <skhan@...uxfoundation.org>,
	linux-kernel-mentees@...ts.linux.dev,
	Gustavo Shahrouzi <gshahrouzi@...il.com>,
	syzkaller-bugs@...glegroups.com,
	syzbot+ff3aa851d46ab82953a3@...kaller.appspotmail.com
Subject: [PATCH] perf/core: Prevent WARN_ON(!ctx) in __free_event for partial init

Move the get_ctx(child_ctx) call and the child_event->ctx assignment to
occur immediately after the child event is allocated. Ensure that
child_event->ctx is non-NULL before any subsequent error path within
inherit_event calls free_event(), satisfying the assumptions of the
cleanup code.

Reported-by: syzbot+ff3aa851d46ab82953a3@...kaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=ff3aa851d46ab82953a3
Signed-off-by: Gabriel Shahrouzi <gshahrouzi@...il.com>
---
 kernel/events/core.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 0bb21659e252..153ba622cfa0 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -14016,6 +14016,9 @@ inherit_event(struct perf_event *parent_event,
 	if (IS_ERR(child_event))
 		return child_event;
 
+	get_ctx(child_ctx);
+	child_event->ctx = child_ctx;
+
 	pmu_ctx = find_get_pmu_context(child_event->pmu, child_ctx, child_event);
 	if (IS_ERR(pmu_ctx)) {
 		free_event(child_event);
@@ -14037,8 +14040,6 @@ inherit_event(struct perf_event *parent_event,
 		return NULL;
 	}
 
-	get_ctx(child_ctx);
-
 	/*
 	 * Make the child state follow the state of the parent event,
 	 * not its attr.disabled bit.  We hold the parent's mutex,
@@ -14059,7 +14060,6 @@ inherit_event(struct perf_event *parent_event,
 		local64_set(&hwc->period_left, sample_period);
 	}
 
-	child_event->ctx = child_ctx;
 	child_event->overflow_handler = parent_event->overflow_handler;
 	child_event->overflow_handler_context
 		= parent_event->overflow_handler_context;
-- 
2.43.0