CVE-2026-89600

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 tasks 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 tasks stack.

Affected Software

References

• https://git.kernel.org/stable/c/66aa9a9e6481bfa512ee5b6380eaaec455a954d2
• https://git.kernel.org/stable/c/b8f73b163b646bc56d4dce9c697a578e333f4894
• https://git.kernel.org/stable/c/d7f1cf5be33ef0175a4e8ed8687aeb98fb00a851