[tip: perf/urgent] perf/core: Fix group leader use-after-free after sibling detach
From: tip-bot2 for Aditya Chillara
Date: Mon Aug 10 2026 - 06:32:20 EST
The following commit has been merged into the perf/urgent branch of tip:
Commit-ID: 42c5ca1f0a288a52878bd72a5595b08261057438
Gitweb: https://git.kernel.org/tip/42c5ca1f0a288a52878bd72a5595b08261057438
Author: Aditya Chillara <aditya.chillara@xxxxxxxxxxxxxxxx>
AuthorDate: Fri, 07 Aug 2026 18:11:52 +05:30
Committer: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Fri, 07 Aug 2026 18:27:05 +02:00
perf/core: Fix group leader use-after-free after sibling detach
perf_group_detach() handles leader and sibling detach differently. When the
group leader is detached, all siblings are promoted to singleton events and
their group_leader pointer is reset to themselves. When a sibling is
detached, it is removed from the leader's sibling_list, but its
group_leader pointer is left pointing at the old leader.
That is harmless when the sibling is being closed and freed immediately, as
in the DETACH_DEAD path. It is not safe when the sibling is detached but
kept alive, such as during CPU hotplug with DETACH_GROUP. In that case the
sibling is removed from the context, while its file descriptor can still
keep it alive.
A typical failing sequence is:
- A group contains leader L and sibling S.
- CPU hot-unplug detaches S with DETACH_GROUP, removing it from
L->sibling_list but leaving S->group_leader == L.
- L is later closed and freed.
- A PERF_IOC_FLAG_GROUP ioctl on S follows S->group_leader and
dereferences the freed leader.
This was reproduced by running the perf event fuzzer, CPU hotplug, and a
stress workload concurrently:
Unable to handle kernel paging request at virtual address 006b6b6b6b6b6cdb
CPU: 2 PID: 12489 Comm: perf_fuzzer 6.18.7 PREEMPT
pc : perf_ioctl+0x34c/0xc68
x20: ffffff89a3fa2c70 x8 : 6b6b6b6b6b6b6b6b
Code: 943c4a0e 340047a0 f9404a94 f9411e88 (f940b908)
Call trace:
perf_ioctl+0x34c/0xc68 (P)
__arm64_sys_ioctl+0xa0/0xf4
invoke_syscall+0x58/0xe4
el0_svc_common+0xa8/0xdc
do_el0_svc+0x1c/0x28
el0_svc+0x40/0xc0
el0t_64_sync_handler+0x68/0xdc
el0t_64_sync+0x1c4/0x1c8
The fault happened in perf_ioctl(), where perf_event_for_each() follows
the stale group_leader pointer and perf_event_for_each_child() then
dereferences the freed leader's context.
Fix the use-after-free by promoting the detached sibling to a singleton.
Also fix __event_disable() cgroup accounting and event state change.
Fixes: 8a49542c0554 ("perf_events: Fix races in group composition")
Assisted-by: PatchWise:gpt-5.5
Signed-off-by: Aditya Chillara <aditya.chillara@xxxxxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Reviewed-by: Dapeng Mi <dapeng1.mi@xxxxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Link: https://patch.msgid.link/20260807-fix-group-leader-uaf-v3-1-b0c2310c9a0d@xxxxxxxxxxxxxxxx
---
kernel/events/core.c | 67 +++++++++++++++++++++++--------------------
1 file changed, 37 insertions(+), 30 deletions(-)
diff --git a/kernel/events/core.c b/kernel/events/core.c
index bd25e19..1a73ba0 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -2343,6 +2343,34 @@ static inline struct list_head *get_event_list(struct perf_event *event)
&event->pmu_ctx->flexible_active;
}
+/* @sibling must already be unlinked from its old leader's sibling_list. */
+static void perf_promote_sibling_to_leader(struct perf_event *sibling,
+ struct perf_event_context *ctx,
+ int group_caps)
+{
+ /*
+ * Events that have PERF_EV_CAP_SIBLING require being part of
+ * a group and cannot exist on their own, schedule them out
+ * and move them into the ERROR state. Also see
+ * _perf_event_enable(), it will not be able to recover this
+ * ERROR state.
+ */
+ if (sibling->event_caps & PERF_EV_CAP_SIBLING)
+ __event_disable(sibling, ctx, PERF_EVENT_STATE_ERROR);
+
+ sibling->group_leader = sibling;
+ sibling->group_caps = group_caps;
+
+ if (sibling->attach_state & PERF_ATTACH_CONTEXT) {
+ add_event_to_groups(sibling, ctx);
+
+ if (sibling->state == PERF_EVENT_STATE_ACTIVE)
+ list_add_tail(&sibling->active_list, get_event_list(sibling));
+ }
+
+ perf_event__header_size(sibling);
+}
+
static void perf_group_detach(struct perf_event *event)
{
struct perf_event *leader = event->group_leader;
@@ -2366,8 +2394,9 @@ static void perf_group_detach(struct perf_event *event)
*/
if (leader != event) {
list_del_init(&event->sibling_list);
- event->group_leader->nr_siblings--;
- event->group_leader->group_generation++;
+ leader->nr_siblings--;
+ leader->group_generation++;
+ perf_promote_sibling_to_leader(event, ctx, event->event_caps);
goto out;
}
@@ -2377,32 +2406,14 @@ static void perf_group_detach(struct perf_event *event)
* to whatever list we are on.
*/
list_for_each_entry_safe(sibling, tmp, &event->sibling_list, sibling_list) {
-
- /*
- * Events that have PERF_EV_CAP_SIBLING require being part of
- * a group and cannot exist on their own, schedule them out
- * and move them into the ERROR state. Also see
- * _perf_event_enable(), it will not be able to recover this
- * ERROR state.
- */
- if (sibling->event_caps & PERF_EV_CAP_SIBLING)
- __event_disable(sibling, ctx, PERF_EVENT_STATE_ERROR);
-
- sibling->group_leader = sibling;
list_del_init(&sibling->sibling_list);
/* Inherit group flags from the previous leader */
- sibling->group_caps = event->group_caps;
-
- if (sibling->attach_state & PERF_ATTACH_CONTEXT) {
- add_event_to_groups(sibling, event->ctx);
-
- if (sibling->state == PERF_EVENT_STATE_ACTIVE)
- list_add_tail(&sibling->active_list, get_event_list(sibling));
- }
+ perf_promote_sibling_to_leader(sibling, ctx, event->group_caps);
WARN_ON_ONCE(sibling->ctx != event->ctx);
}
+ event->nr_siblings = 0;
out:
for_each_sibling_event(tmp, leader)
@@ -2592,12 +2603,7 @@ __perf_remove_from_context(struct perf_event *event,
if (flags & DETACH_DEAD)
state = PERF_EVENT_STATE_DEAD;
- event_sched_out(event, ctx);
-
- if (event->state > PERF_EVENT_STATE_OFF)
- perf_cgroup_event_disable(event, ctx);
-
- perf_event_set_state(event, min(event->state, state));
+ __event_disable(event, ctx, state);
if (flags & DETACH_GROUP)
perf_group_detach(event);
@@ -2666,8 +2672,9 @@ static void __event_disable(struct perf_event *event,
enum perf_event_state state)
{
event_sched_out(event, ctx);
- perf_cgroup_event_disable(event, ctx);
- perf_event_set_state(event, state);
+ if (event->state > PERF_EVENT_STATE_OFF)
+ perf_cgroup_event_disable(event, ctx);
+ perf_event_set_state(event, min(event->state, state));
}
/*