CVE-2026-68174tracing: Fix union collision of module and refcnt for dynamic events

Official description

In the Linux kernel, the following vulnerability has been resolved: tracing: Fix union collision of module and refcnt for dynamic events In 'struct trace_event_call', the 'module' pointer and the 'refcnt' atomic variable share the same memory space in a union. For dynamic events, the union member is 'refcnt', which acts as an active reference counter. When a dynamic event (such as kprobe, uprobe, fprobe, eprobe, or wprobe) has a non-zero reference count (e.g. due to active event triggers or perf attachments), its 'call->module' evaluates to a small non-zero integer instead of NULL. When filtering or setting events for a specific module (e.g., writing ':mod:<module>' to 'set_event'), the code in '__ftrace_set_clr_event_nolock()' and 'update_event_fields()' reads 'call->module' directly without checking whether the event is dynamic. This causes the kernel to treat the small integer (refcnt) as a 'struct module' pointer, leading to a NULL/invalid pointer dereference (Oops) when dereferencing the module name. Fix this by ensuring that the 'TRACE_EVENT_FL_DYNAMIC' flag is checked before treating 'call->module' as a valid pointer in these code paths.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/b6a4575f22925da7e6aa00171e9fc0e5029c0bc9
• https://git.kernel.org/stable/c/43a23dfe0024afd3d2b0232e987d0292919a9b24
• https://git.kernel.org/stable/c/b4eb07bde606c2096b24252be589e735eff6d413