CVE-2026-99179watch_queue: Fix note pool publication race in watch_queue_set_size()

Official description

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.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/2137d487b25eefa862be70de489b64f4c679fe1f
• https://git.kernel.org/stable/c/6aaa6c1a1b61aae332d6e7e0083140b86ea51e14
• https://git.kernel.org/stable/c/4b20867d80e7e91fb7db531f34035d91591ba405
• https://git.kernel.org/stable/c/da52e5fcb2cae6acdc0d5722ff83499f8232b9d1
• https://git.kernel.org/stable/c/f94c45f83e688e41dfe1b3a589806a0a25567260
• https://git.kernel.org/stable/c/811fb6d0b07605e8e8d93bde8748be4b3028809a
• https://git.kernel.org/stable/c/9e73a6754457ffed8399b835552013b9363e51d1
• https://git.kernel.org/stable/c/5e531d62f1f8834faf7a4eed0d41105cf6570a8f