From: Aditya Chillara <aditya.chillara@oss.qualcomm.com> stable inclusion from stable-v7.2 commit 42c5ca1f0a288a52878bd72a5595b08261057438 category: bugfix bugzilla: https://atomgit.com/src-openeuler/kernel/issues/18309 CVE: CVE-2026-74637 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=... ---------------------------------------------------------------------- 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@oss.qualcomm.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Dapeng Mi <dapeng1.mi@linux.intel.com> Cc: stable@vger.kernel.org Link: https://patch.msgid.link/20260807-fix-group-leader-uaf-v3-1-b0c2310c9a0d@oss... Conflicts: kernel/events/core.c [Fix simple ctx diff.] Signed-off-by: Luo Gengkun <luogengkun2@huawei.com> --- kernel/events/core.c | 66 +++++++++++++++++++++++++------------------- 1 file changed, 37 insertions(+), 29 deletions(-) diff --git a/kernel/events/core.c b/kernel/events/core.c index 6916dc78b0e7..9a779ca76798 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -2163,6 +2163,34 @@ 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; @@ -2186,8 +2214,9 @@ 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; } @@ -2197,32 +2226,14 @@ 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) @@ -2389,12 +2400,8 @@ __perf_remove_from_context(struct perf_event *event, if (flags & DETACH_DEAD) state = PERF_EVENT_STATE_DEAD; - event_sched_out(event, ctx); + __event_disable(event, ctx, state); - if (event->state > PERF_EVENT_STATE_OFF) - perf_cgroup_event_disable(event, ctx); - - perf_event_set_state(event, min(event->state, state)); if (flags & DETACH_GROUP) perf_group_detach(event); if (flags & DETACH_CHILD) @@ -2463,8 +2470,9 @@ 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)); } /* -- 2.34.1