HIGH Introduced in 6.4
tracing UserEvents UAF
CVE-2026-89750
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
KernelScan AI7.0HIGH
01Description
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.
02KernelScan AI Analysis
Risk summary
A local unprivileged user can trigger a use-after-free in the user_events tracing subsystem by forking a process under memory pressure that causes user_event_mm_alloc() to fail during task duplication. This leads to a dangling pointer that, when the child exits, frees memory still referenced by the parent, potentially enabling kernel code execution or denial of service.
Vulnerability analysis
When a process that has active tracing state forks, the kernel copies a pointer to that data into the child without ensuring the child has its own independent claim on the memory. The child is supposed to receive a separate copy, but if the system runs out of memory during that setup, the copied pointer remains in place. Later, when the child exits, its teardown frees memory on behalf of the parent, leaving the parent pointing to freed space. The parent then triggers a use-after-free when it next touches its own tracing state. The fix wipes the copied pointer before the allocation is attempted, so a failed setup leaves the child with no pointer to mistakenly release. Any local user who can reach the user_events interface through a standard ioctl can trigger this.
Lifecycle
03Fix Versions
| Branch | Introduced | Fixed in | Patch commit |
|---|---|---|---|
| 6.12 | 6.4 | 6.12.109 | 63b39e49a4c9 |
| 6.18 | 6.4 | 6.18.50 | 25a0758cf6bd |
| 6.6 | 6.4 | 6.6.157 | 33ce55b368b6 |
| 7.2 | 6.4 | 7.2.4 | b799f67119af |
| mainline | 6.4 | 7.3 | 390f6bd8583d |
| cip/6.12 | 6.4 | 6.12.111-cip32 | 63b39e49a4c9 |
04CIP Kernels
State of the newest release of each Civil Infrastructure Platform SLTS tree, from CIP's own fix records.
| CIP tree | State |
|---|---|
| cip/6.12 | Fixed in 6.12.111-cip32 |