CVE-2026-98821 block: reject polled dio with user integrity metadata
A local attacker can trigger a kernel crash via null pointer dereference in the block layer when using polled direct I/O with integrity metadata.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-98821?
CVE-2026-98821 is a vulnerability in Linux, published on 18 Oct 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
block: reject polled dio with user integrity metadata
IOCB_HAS_METADATA leaves iocb->private as a uio_meta, while iocb_bio_iopoll() expects a bio. Since 2729a60bbfb9, metadata I/O always uses __blkdev_direct_IO(), which never publishes the bio for polling, so IOPOLL calls bio_poll() on the uio_meta.
Reproducer: io_uring IOPOLL plus a PI attribute on an integrity device (scsi_debug dif=1 dix=1). KASAN reports:
Oops: general protection fault, probably for non-canonical address 0xdffffc0000000004 KASAN: null-ptr-deref in range [0x0000000000000020-0x0000000000000027] RIP: 0010:bio_poll+0x9d/0x4b0 Call Trace: iocb_bio_iopoll+0x5b/0x80 io_uring_classic_poll+0xf3/0x140 io_do_iopoll+0x4e3/0xc00 io_iopoll_check+0x275/0x560 __do_sys_io_uring_enter+0x2e5/0x720
Return -EOPNOTSUPP when HIPRI is combined with user metadata.
Which versions are affected by CVE-2026-98821?
How do I fix CVE-2026-98821?
Apply the vendor's patch.
Is CVE-2026-98821 being exploited?
There is no known exploitation of CVE-2026-98821 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-98821, DEBIAN-CVE-2026-98821, GHSA-4mqf-mrhr-h3rh, UBUNTU-CVE-2026-98821.