Note pool publication race in Linux kernel watch_queue_set_size()
CVE-2026-99179 Published on October 28, 2026
watch_queue: Fix note pool publication race in watch_queue_set_size()
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.
Products Associated with CVE-2026-99179
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Affected Versions
Linux:- Version c73be61cede5882f9605a852414db559c0ebedfd and below 811fb6d0b07605e8e8d93bde8748be4b3028809a is affected.
- Version c73be61cede5882f9605a852414db559c0ebedfd and below 9e73a6754457ffed8399b835552013b9363e51d1 is affected.
- Version c73be61cede5882f9605a852414db559c0ebedfd and below 5e531d62f1f8834faf7a4eed0d41105cf6570a8f is affected.
- Version 5.8 is affected.
- Before 5.8 is unaffected.
- Version 6.18.59, <= 6.18.* is unaffected.
- Version 7.2.13, <= 7.2.* is unaffected.
- Version 7.3, <= * is unaffected.