* [PATCH] perf/core: Fix group leader use-after-free after sibling detach
@ 2026-06-26 9:54 Aditya Chillara
2026-06-29 2:58 ` Mi, Dapeng
0 siblings, 1 reply; 5+ messages in thread
From: Aditya Chillara @ 2026-06-26 9:54 UTC (permalink / raw)
To: Peter Zijlstra, Ingo Molnar, Arnaldo Carvalho de Melo,
Namhyung Kim, Mark Rutland, Alexander Shishkin, Jiri Olsa,
Ian Rogers, Adrian Hunter, James Clark
Cc: Peter Zijlstra, Ingo Molnar, linux-perf-users, linux-kernel,
stable, Aditya Chillara
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.
Fixes: 8a49542c0554 ("perf_events: Fix races in group composition")
Assisted-by: PatchWise:gpt-5.5
Signed-off-by: Aditya Chillara <aditya.chillara@oss.qualcomm.com>
---
kernel/events/core.c | 20 ++++++++++++++++++++
1 file changed, 20 insertions(+)
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 954c36e28101..dd9892040ab2 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -2605,6 +2605,26 @@ __perf_remove_from_context(struct perf_event *event,
perf_child_detach(event);
list_del_event(event, ctx);
+ if ((flags & DETACH_GROUP) && event->group_leader != event) {
+ /*
+ * list_del_event() needed the old group_leader to tell a real
+ * leader from a sibling. That's done now, so make the detached
+ * sibling self-contained.
+ */
+ event->group_leader = event;
+ event->group_caps = event->event_caps;
+
+ /*
+ * PERF_EV_CAP_SIBLING event requires being part of a group, so move
+ * the event to ERROR state if it is still alive.
+ */
+ if ((event->event_caps & PERF_EV_CAP_SIBLING) &&
+ event->state > PERF_EVENT_STATE_ERROR)
+ perf_event_set_state(event, PERF_EVENT_STATE_ERROR);
+
+ perf_event__header_size(event);
+ }
+
if (!pmu_ctx->nr_events) {
pmu_ctx->rotate_necessary = 0;
---
base-commit: ab9de95c9cf952332ab79453b4b5d1bfca8e514f
change-id: 20260626-fix-group-leader-uaf-c46960e525e0
Best regards,
--
Aditya Chillara <aditya.chillara@oss.qualcomm.com>
^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH] perf/core: Fix group leader use-after-free after sibling detach
2026-06-26 9:54 [PATCH] perf/core: Fix group leader use-after-free after sibling detach Aditya Chillara
@ 2026-06-29 2:58 ` Mi, Dapeng
2026-06-29 4:00 ` Aditya Chillara
0 siblings, 1 reply; 5+ messages in thread
From: Mi, Dapeng @ 2026-06-29 2:58 UTC (permalink / raw)
To: Aditya Chillara, Peter Zijlstra, Ingo Molnar,
Arnaldo Carvalho de Melo, Namhyung Kim, Mark Rutland,
Alexander Shishkin, Jiri Olsa, Ian Rogers, Adrian Hunter,
James Clark
Cc: Peter Zijlstra, Ingo Molnar, linux-perf-users, linux-kernel,
stable
On 6/26/2026 5:54 PM, Aditya Chillara wrote:
> 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.
>
> Fixes: 8a49542c0554 ("perf_events: Fix races in group composition")
> Assisted-by: PatchWise:gpt-5.5
> Signed-off-by: Aditya Chillara <aditya.chillara@oss.qualcomm.com>
> ---
> kernel/events/core.c | 20 ++++++++++++++++++++
> 1 file changed, 20 insertions(+)
>
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 954c36e28101..dd9892040ab2 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -2605,6 +2605,26 @@ __perf_remove_from_context(struct perf_event *event,
> perf_child_detach(event);
> list_del_event(event, ctx);
>
> + if ((flags & DETACH_GROUP) && event->group_leader != event) {
> + /*
> + * list_del_event() needed the old group_leader to tell a real
> + * leader from a sibling. That's done now, so make the detached
> + * sibling self-contained.
> + */
> + event->group_leader = event;
> + event->group_caps = event->event_caps;
> +
> + /*
> + * PERF_EV_CAP_SIBLING event requires being part of a group, so move
> + * the event to ERROR state if it is still alive.
> + */
> + if ((event->event_caps & PERF_EV_CAP_SIBLING) &&
> + event->state > PERF_EVENT_STATE_ERROR)
> + perf_event_set_state(event, PERF_EVENT_STATE_ERROR);
> +
> + perf_event__header_size(event);
> + }
> +
Why not move this part of fixing code into perf_group_detach()? It seems a
better place to fix the issue. Thanks.
> if (!pmu_ctx->nr_events) {
> pmu_ctx->rotate_necessary = 0;
>
>
> ---
> base-commit: ab9de95c9cf952332ab79453b4b5d1bfca8e514f
> change-id: 20260626-fix-group-leader-uaf-c46960e525e0
>
> Best regards,
> --
> Aditya Chillara <aditya.chillara@oss.qualcomm.com>
>
>
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] perf/core: Fix group leader use-after-free after sibling detach
2026-06-29 2:58 ` Mi, Dapeng
@ 2026-06-29 4:00 ` Aditya Chillara
2026-06-29 7:06 ` Mi, Dapeng
0 siblings, 1 reply; 5+ messages in thread
From: Aditya Chillara @ 2026-06-29 4:00 UTC (permalink / raw)
To: Mi, Dapeng, Peter Zijlstra, Ingo Molnar, Arnaldo Carvalho de Melo,
Namhyung Kim, Mark Rutland, Alexander Shishkin, Jiri Olsa,
Ian Rogers, Adrian Hunter, James Clark
Cc: Peter Zijlstra, Ingo Molnar, linux-perf-users, linux-kernel,
stable
On 6/29/2026 8:28 AM, Mi, Dapeng wrote:
>
> On 6/26/2026 5:54 PM, Aditya Chillara wrote:
>> 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.
>>
>> Fixes: 8a49542c0554 ("perf_events: Fix races in group composition")
>> Assisted-by: PatchWise:gpt-5.5
>> Signed-off-by: Aditya Chillara <aditya.chillara@oss.qualcomm.com>
>> ---
>> kernel/events/core.c | 20 ++++++++++++++++++++
>> 1 file changed, 20 insertions(+)
>>
>> diff --git a/kernel/events/core.c b/kernel/events/core.c
>> index 954c36e28101..dd9892040ab2 100644
>> --- a/kernel/events/core.c
>> +++ b/kernel/events/core.c
>> @@ -2605,6 +2605,26 @@ __perf_remove_from_context(struct perf_event *event,
>> perf_child_detach(event);
>> list_del_event(event, ctx);
>>
>> + if ((flags & DETACH_GROUP) && event->group_leader != event) {
>> + /*
>> + * list_del_event() needed the old group_leader to tell a real
>> + * leader from a sibling. That's done now, so make the detached
>> + * sibling self-contained.
>> + */
>> + event->group_leader = event;
>> + event->group_caps = event->event_caps;
>> +
>> + /*
>> + * PERF_EV_CAP_SIBLING event requires being part of a group, so move
>> + * the event to ERROR state if it is still alive.
>> + */
>> + if ((event->event_caps & PERF_EV_CAP_SIBLING) &&
>> + event->state > PERF_EVENT_STATE_ERROR)
>> + perf_event_set_state(event, PERF_EVENT_STATE_ERROR);
>> +
>> + perf_event__header_size(event);
>> + }
>> +
>
> Why not move this part of fixing code into perf_group_detach()? It seems a
> better place to fix the issue. Thanks.
Because list_del_event() just above my change does:
if (event->group_leader == event)
del_event_from_groups(event, ctx);
so resetting the group leader in perf_group_detach() would attempt removing sibling
event->group_node from a group rb-tree it was never added to (only leader gets added
in list_add_event()).
Thank you,
Aditya
>
>
>> if (!pmu_ctx->nr_events) {
>> pmu_ctx->rotate_necessary = 0;
>>
>>
>> ---
>> base-commit: ab9de95c9cf952332ab79453b4b5d1bfca8e514f
>> change-id: 20260626-fix-group-leader-uaf-c46960e525e0
>>
>> Best regards,
>> --
>> Aditya Chillara <aditya.chillara@oss.qualcomm.com>
>>
>>
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] perf/core: Fix group leader use-after-free after sibling detach
2026-06-29 4:00 ` Aditya Chillara
@ 2026-06-29 7:06 ` Mi, Dapeng
2026-06-29 19:15 ` Aditya Chillara
0 siblings, 1 reply; 5+ messages in thread
From: Mi, Dapeng @ 2026-06-29 7:06 UTC (permalink / raw)
To: Aditya Chillara, Peter Zijlstra, Ingo Molnar,
Arnaldo Carvalho de Melo, Namhyung Kim, Mark Rutland,
Alexander Shishkin, Jiri Olsa, Ian Rogers, Adrian Hunter,
James Clark
Cc: Peter Zijlstra, Ingo Molnar, linux-perf-users, linux-kernel,
stable
On 6/29/2026 12:00 PM, Aditya Chillara wrote:
> On 6/29/2026 8:28 AM, Mi, Dapeng wrote:
>> On 6/26/2026 5:54 PM, Aditya Chillara wrote:
>>> 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.
>>>
>>> Fixes: 8a49542c0554 ("perf_events: Fix races in group composition")
>>> Assisted-by: PatchWise:gpt-5.5
>>> Signed-off-by: Aditya Chillara <aditya.chillara@oss.qualcomm.com>
>>> ---
>>> kernel/events/core.c | 20 ++++++++++++++++++++
>>> 1 file changed, 20 insertions(+)
>>>
>>> diff --git a/kernel/events/core.c b/kernel/events/core.c
>>> index 954c36e28101..dd9892040ab2 100644
>>> --- a/kernel/events/core.c
>>> +++ b/kernel/events/core.c
>>> @@ -2605,6 +2605,26 @@ __perf_remove_from_context(struct perf_event *event,
>>> perf_child_detach(event);
>>> list_del_event(event, ctx);
>>>
>>> + if ((flags & DETACH_GROUP) && event->group_leader != event) {
>>> + /*
>>> + * list_del_event() needed the old group_leader to tell a real
>>> + * leader from a sibling. That's done now, so make the detached
>>> + * sibling self-contained.
>>> + */
>>> + event->group_leader = event;
>>> + event->group_caps = event->event_caps;
>>> +
>>> + /*
>>> + * PERF_EV_CAP_SIBLING event requires being part of a group, so move
>>> + * the event to ERROR state if it is still alive.
>>> + */
>>> + if ((event->event_caps & PERF_EV_CAP_SIBLING) &&
>>> + event->state > PERF_EVENT_STATE_ERROR)
>>> + perf_event_set_state(event, PERF_EVENT_STATE_ERROR);
>>> +
>>> + perf_event__header_size(event);
>>> + }
>>> +
>> Why not move this part of fixing code into perf_group_detach()? It seems a
>> better place to fix the issue. Thanks.
> Because list_del_event() just above my change does:
>
> if (event->group_leader == event)
> del_event_from_groups(event, ctx);
>
> so resetting the group leader in perf_group_detach() would attempt removing sibling
> event->group_node from a group rb-tree it was never added to (only leader gets added
> in list_add_event()).
Yeah, but I don't see why we can't do same thing for the sibling event
detaching in perf_group_detach(). Just like the group leader detaching,
each sibling event would be re-added into ctx groups by calling
add_event_to_groups(). Suppose we can do same thing for the sibling event
detaching, call add_event_to_groups() to add the standalone event into ctx
groups, right?
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));
}
>
> Thank you,
> Aditya
>
>>
>>> if (!pmu_ctx->nr_events) {
>>> pmu_ctx->rotate_necessary = 0;
>>>
>>>
>>> ---
>>> base-commit: ab9de95c9cf952332ab79453b4b5d1bfca8e514f
>>> change-id: 20260626-fix-group-leader-uaf-c46960e525e0
>>>
>>> Best regards,
>>> --
>>> Aditya Chillara <aditya.chillara@oss.qualcomm.com>
>>>
>>>
>
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] perf/core: Fix group leader use-after-free after sibling detach
2026-06-29 7:06 ` Mi, Dapeng
@ 2026-06-29 19:15 ` Aditya Chillara
0 siblings, 0 replies; 5+ messages in thread
From: Aditya Chillara @ 2026-06-29 19:15 UTC (permalink / raw)
To: Mi, Dapeng, Peter Zijlstra, Ingo Molnar, Arnaldo Carvalho de Melo,
Namhyung Kim, Mark Rutland, Alexander Shishkin, Jiri Olsa,
Ian Rogers, Adrian Hunter, James Clark
Cc: Peter Zijlstra, Ingo Molnar, linux-perf-users, linux-kernel,
stable
On 6/29/2026 12:36 PM, Mi, Dapeng wrote:
>
> On 6/29/2026 12:00 PM, Aditya Chillara wrote:
>> On 6/29/2026 8:28 AM, Mi, Dapeng wrote:
>>> On 6/26/2026 5:54 PM, Aditya Chillara wrote:
>>>> 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.
>>>>
>>>> Fixes: 8a49542c0554 ("perf_events: Fix races in group composition")
>>>> Assisted-by: PatchWise:gpt-5.5
>>>> Signed-off-by: Aditya Chillara <aditya.chillara@oss.qualcomm.com>
>>>> ---
>>>> kernel/events/core.c | 20 ++++++++++++++++++++
>>>> 1 file changed, 20 insertions(+)
>>>>
>>>> diff --git a/kernel/events/core.c b/kernel/events/core.c
>>>> index 954c36e28101..dd9892040ab2 100644
>>>> --- a/kernel/events/core.c
>>>> +++ b/kernel/events/core.c
>>>> @@ -2605,6 +2605,26 @@ __perf_remove_from_context(struct perf_event *event,
>>>> perf_child_detach(event);
>>>> list_del_event(event, ctx);
>>>>
>>>> + if ((flags & DETACH_GROUP) && event->group_leader != event) {
>>>> + /*
>>>> + * list_del_event() needed the old group_leader to tell a real
>>>> + * leader from a sibling. That's done now, so make the detached
>>>> + * sibling self-contained.
>>>> + */
>>>> + event->group_leader = event;
>>>> + event->group_caps = event->event_caps;
>>>> +
>>>> + /*
>>>> + * PERF_EV_CAP_SIBLING event requires being part of a group, so move
>>>> + * the event to ERROR state if it is still alive.
>>>> + */
>>>> + if ((event->event_caps & PERF_EV_CAP_SIBLING) &&
>>>> + event->state > PERF_EVENT_STATE_ERROR)
>>>> + perf_event_set_state(event, PERF_EVENT_STATE_ERROR);
>>>> +
>>>> + perf_event__header_size(event);
>>>> + }
>>>> +
>>> Why not move this part of fixing code into perf_group_detach()? It seems a
>>> better place to fix the issue. Thanks.
>> Because list_del_event() just above my change does:
>>
>> if (event->group_leader == event)
>> del_event_from_groups(event, ctx);
>>
>> so resetting the group leader in perf_group_detach() would attempt removing sibling
>> event->group_node from a group rb-tree it was never added to (only leader gets added
>> in list_add_event()).
>
> Yeah, but I don't see why we can't do same thing for the sibling event
> detaching in perf_group_detach(). Just like the group leader detaching,
> each sibling event would be re-added into ctx groups by calling
> add_event_to_groups(). Suppose we can do same thing for the sibling event
> detaching, call add_event_to_groups() to add the standalone event into ctx
> groups, right?
Yup, that's a cleaner fix, sent v2!
Thank you,
Aditya
>
>
> 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));
> }
>
>
>>>
>>>> if (!pmu_ctx->nr_events) {
>>>> pmu_ctx->rotate_necessary = 0;
>>>>
>>>>
>>>> ---
>>>> base-commit: ab9de95c9cf952332ab79453b4b5d1bfca8e514f
>>>> change-id: 20260626-fix-group-leader-uaf-c46960e525e0
>>>>
>>>> Best regards,
>>>> --
>>>> Aditya Chillara <aditya.chillara@oss.qualcomm.com>
>>>>
>>>>
>>
^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2026-06-29 19:15 UTC | newest]
Thread overview: 5+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2026-06-26 9:54 [PATCH] perf/core: Fix group leader use-after-free after sibling detach Aditya Chillara
2026-06-29 2:58 ` Mi, Dapeng
2026-06-29 4:00 ` Aditya Chillara
2026-06-29 7:06 ` Mi, Dapeng
2026-06-29 19:15 ` Aditya Chillara
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