The patch below does not apply to the 5.10-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <[email protected]>.
To reproduce the conflict and resubmit, you may use the following commands:
git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.10.y
git checkout FETCH_HEAD
git cherry-pick -x 42c5ca1f0a288a52878bd72a5595b08261057438
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026081732-unmixed-crudely-500c@gregkh' --subject-prefix 'PATCH 5.10.y' 'HEAD^..'
Possible dependencies:
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From 42c5ca1f0a288a52878bd72a5595b08261057438 Mon Sep 17 00:00:00 2001
From: Aditya Chillara <[email protected]>
Date: Fri, 7 Aug 2026 18:11:52 +0530
Subject: [PATCH] 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 <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Reviewed-by: Dapeng Mi <[email protected]>
Cc: [email protected]
Link: https://patch.msgid.link/[email protected]
diff --git a/kernel/events/core.c b/kernel/events/core.c
index bd25e1998faf..1a73ba0747df 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));
}
/*
lmpx.com only provides a reader for public news (NNTP) servers. It is not
affiliated with the servers or forums shown here and is not responsible for
the content of articles, which is written by their respective authors.