CVE-2026-64556

In the Linux kernel, the following vulnerability has been resolved:

perf/core: Detach event groups during removeonexec

perfeventremoveonexec() removes events by calling perfeventexitevent(). For top-level events, this removes the event from the context with DETACHEXIT only.

This can leave inconsistent group state when a removed event is a group leader and the group contains siblings without removeonexec. If the group was active, the surviving siblings can remain active and attached to the removed leader's sibling list, but are no longer represented by a valid group leader on the PMU context active lists.

A later close of the removed leader uses DETACHGROUP and can promote the still-active siblings from this stale group state. The next schedule-in can then add an already-linked activelist entry again, corrupting the PMU context active list.

With DEBUGLIST enabled, this is caught as a listadd double-add in mergeschedin().

Fix this by detaching group relationships when removeonexec removes an event. This preserves the existing task-exit and revoke behavior, while ensuring surviving siblings are ungrouped before the removed event leaves the context.