watch_queue: Fix note pool publication race in watch_queue_set_size()

Summary

In the Linux kernel, the following vulnerability has been resolved: watch_queue: Fix note pool publication race in watch_queue_set_size() There is a race between watch_queue_set_size() and post_one_notification(). watch_queue_set_size() publishes wqueue->notes, notes_bitmap, nr_pages and nr_notes with plain stores, and post_one_notification() reads them with plain loads under a different lock, so nothing orders the four stores against the poster's loads: depending on the build, notes can be stored last (gcc 14 on x86-64 does this). Since keyctl_watch_key() lets a watch attach to a queue before it is sized, post_one_notification() can already be running on another CPU at that moment: it reads nr_notes > 0, passes its bounds check, and then reads notes while it is still NULL, dereferencing notes[0]. An unprivileged user triggers this reliably by watching one of its own keys through a notification pipe and racing ioctl(IOC_WATCH_QUEUE_SET_SIZE) on that pipe against keyctl(KEYCTL_SETPERM) on the key from another CPU, triggering: BUG: kernel NULL pointer dereference, address: 0000000000000000 RIP: 0010:post_one_notification.isra.0+0xa2/0x1e0 Call Trace: __post_watch_notification+0x148/0x180 keyctl_setperm_key+0x119/0x130 do_syscall_64+0x108/0x4c0 entry_SYSCALL_64_after_hwframe+0x77/0x7f Kernel panic - not syncing: Fatal exception in interrupt Fix this by publishing nr_notes last with smp_store_release(), and by reading it once with smp_load_acquire() in post_one_notification() before the bitmap and the page array are touched. A poster that observes a non-zero nr_notes then also observes the pool behind it; one that observes zero drops the notification as before.

Timeline

1. Oct 28, 2026, 10:35 AM UTCCVE published
2. Oct 28, 2026, 10:41 AM UTCFirst seen by cve.now
3. Oct 30, 2026, 12:42 PM UTCRecord last updated

Affected versions

• Linux Linux

  Version range not reported

• Linux Linux

  5.8

• KernelLinux

  From 5.8.0 · fixed in 6.18.59; From 6.19.0 · fixed in 7.2.13

References 8