[tip: perf/urgent] perf: Fix null pointer access in is_include_guest_event()

The following commit has been merged into the perf/urgent branch of tip:

Commit-ID:     88aed0422f39b22406f35f1e758cea25e7bbcfb5
Gitweb:        https://git.kernel.org/tip/88aed0422f39b22406f35f1e758cea25e7bbcfb5
Author:        Vinay Belgaumkar <[email protected]>
AuthorDate:    Fri, 04 Sep 2026 11:16:24 -07:00
Committer:     Peter Zijlstra <[email protected]>
CommitterDate: Fri, 18 Sep 2026 12:19:43 +02:00

perf: Fix null pointer access in is_include_guest_event()

A typical module unload occurring event when there is an active perf
connection leads to freeing of the pmu pointer. The call log is something
like:
 ..
 __pmu_detach_event
 pmu_detach_event
 pmu_detach_events
 perf_pmu_unregister
 ..

__pmu_detach_event() sets event->pmu to null. When the perf connection
finally is closed, the following stack trace is observed:

 Oops: general protection fault, kernel NULL pointer dereference
 ...
 RIP: 0010:_free_event+0x3e/0x370
 ...
 Call Trace:
 ...
 perf_event_release_kernel+0x260/0x2d0
 perf_release+0x12/0x20

A call to mediated_pmu_unaccount_event() inside _free_event() is the root
cause of this crash. Adding a check inside is_include_guest_event() ensures
we don't accidentally access a null pmu ptr. In addition to this, we will
now call mediated_pmu_unaccount_event() before clearing the pmu ptr so that
nr_include_guest_events counts are maintained correctly.

Fixes: eff95e170275 ("perf: Add APIs to create/release mediated guest vPMUs")
Assisted-by: Claude:Claude-Sonnet-5
Signed-off-by: Vinay Belgaumkar <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Reviewed-by: Dapeng Mi <[email protected]>
Link: https://patch.msgid.link/[email protected]
---
 kernel/events/core.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index fe33fe1..db7b76d 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -6350,6 +6350,9 @@ static DEFINE_MUTEX(perf_mediated_pmu_mutex);
 /* !exclude_guest event of PMU with PERF_PMU_CAP_MEDIATED_VPMU */
 static inline bool is_include_guest_event(struct perf_event *event)
 {
+	if (!event->pmu)
+		return false;
+
 	if ((event->pmu->capabilities & PERF_PMU_CAP_MEDIATED_VPMU) &&
 	    !event->attr.exclude_guest)
 		return true;
@@ -13002,6 +13005,7 @@ static void __pmu_detach_event(struct pmu *pmu, struct perf_event *event,
 	exclusive_event_destroy(event);
 	module_put(pmu->module);
 
+	mediated_pmu_unaccount_event(event);
 	event->pmu = NULL; /* force fault instead of UAF */
 }