HIGH Introduced in 6.14
fanotify PermEvent UAF
CVE-2026-89600
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
KernelScan AI6.0MEDIUM
01Description
In the Linux kernel, the following vulnerability has been resolved: fanotify: fix use-after-free of file range info fsnotify_pre_content() builds its file_range on the triggering task's stack. fanotify_alloc_perm_event() saves a pointer to range.pos in the heap-allocated permission event so copy_range_info_to_user() can report the offset later. The event reader can set the event state to FAN_EVENT_REPORTED and then sleep while preparing the file descriptor. If a signal interrupts the triggering task at that point, fanotify_get_response() changes the state to FAN_EVENT_CANCELED and returns. This unwinds the file_range stack frame while the reader still owns the event. The reader then dereferences pevent->ppos and copies the stale stack value to userspace. KASAN reported: BUG: KASAN: use-after-free in fanotify_read+0x293e/0x2970 Read of size 8 at addr ffff88811434fc50 by task fanotify_inotif/95 Call Trace: fanotify_read+0x293e/0x2970 vfs_read+0x177/0xa20 ksys_read+0xf7/0x1c0 do_syscall_64+0xf9/0x540 entry_SYSCALL_64_after_hwframe+0x77/0x7f Store the range position directly in the permission event and use FANOTIFY_NO_RANGE when range information is unavailable. The event remains alive until the reader finishes, so the reported offset no longer depends on the triggering task's stack.
02KernelScan AI Analysis
Risk summary
A local user who can set up a fanotify pre-content watch and trigger file access events can exploit a race between the event reader and the triggering task to read a stale stack pointer, resulting in a use-after-free. The bug requires the fanotify pre-content event feature (introduced in 6.14) and a carefully timed signal to cancel the triggering task while the reader still holds the event. The impact is memory corruption that could lead to information disclosure or data integrity violations.
Vulnerability analysis
A race condition in fanotify pre-content events lets the event reader hold a pointer to an offset that lives on the triggering task’s stack. If the triggering task is interrupted by a signal while the reader is still preparing the response, the stack frame is unwound and the reader later follows the stale pointer, copying an out-of-scope stack value to userspace. The fix copies the offset directly into the heap-allocated event structure rather than keeping a pointer to the trigger’s stack, and uses a sentinel value when no range information is present. A local process that can set up a fanotify pre-content watch and access files on watched paths can reach this; no special privileges are needed beyond creating the watch.
Lifecycle
03Fix Versions
| Branch | Introduced | Fixed in | Patch commit |
|---|---|---|---|
| 6.18 | 6.14 | 6.18.50 | 66aa9a9e6481 |
| 7.2 | 6.14 | 7.2.4 | b8f73b163b64 |
| mainline | 6.14 | 7.3 | d7f1cf5be33e |