CVE-2026-89750tracing/user_events: Clear copied tracing state before fork duplication

Official description

In the Linux kernel, the following vulnerability has been resolved: tracing/user_events: Clear copied tracing state before fork duplication dup_task_struct() copies user_event_mm from the parent into the child, without grabbing a reference to it. user_event_mm_dup() should replace it, but it leaves that copied pointer unmodified if user_event_mm_alloc() fails. When the child exits, user_event_mm_remove() decrements a reference the child never owned, which ultimately frees user_event_mm, while the parent still as a stale pointer to it. This creates a UAF, which KASAN reports as: BUG: KASAN: slab-use-after-free in current_user_event_mm+0x51/0x1d0 Write of size 4 at addr ffff888005010d30 by task init/44 Call Trace: <TASK> kasan_report+0xce/0x100 kasan_check_range+0x10f/0x1e0 current_user_event_mm+0x51/0x1d0 user_events_ioctl+0x82e/0x15c0 __x64_sys_ioctl+0x139/0x1c0 do_syscall_64+0xce/0x450 entry_SYSCALL_64_after_hwframe+0x77/0x7f Allocated by task 44: __kasan_kmalloc+0x8f/0xa0 __kmalloc_cache_noprof+0x180/0x3a0 user_event_mm_alloc+0x3c/0x1f0 current_user_event_mm+0x88/0x1d0 Freed by task 42: __kasan_slab_free+0x43/0x70 kfree+0x13a/0x390 process_one_work+0x696/0xf90 worker_thread+0x420/0xba0 The fix simply clears the copied pointer before any possible failure. In case of failure, the child then has nothing to free.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/33ce55b368b64d65941867add00e7f288cbb8234
• https://git.kernel.org/stable/c/63b39e49a4c9d68e010e96b26fc7374f0864f2b1
• https://git.kernel.org/stable/c/25a0758cf6bdbfddac2be71124c9bd0692f4b0b1
• https://git.kernel.org/stable/c/b799f67119aff179719a0b1e12441ebbdaaf62f9
• https://git.kernel.org/stable/c/390f6bd8583d177029d9df4bea6667509e55a765