CVE-2026-90181 ublk: avoid teardown retry loop on xarray allocation failure

What is CVE-2026-90181?

CVE-2026-90181 is a denial of service vulnerability in Linux, published on 17 Sep 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:

ublk: avoid teardown retry loop on xarray allocation failure

__ublk_shmem_remove_ranges() removes matching maple tree ranges in batches, but first stores each range into a temporary xarray so that the pages can be unpinned after dropping the maple tree lock.

That temporary xarray is filled under the maple tree lock with xa_store(..., GFP_ATOMIC). If the store fails before mas_erase(), the current range is left in the tree and the helper returns false. The outer ublk_shmem_remove_ranges() loop then immediately retries the same range. While the atomic allocation keeps failing, the teardown path has no forward progress.

The issue can be reproduced with radix_tree_node failslab injection after a SHMEM_ZC buffer has already been registered:

# Kernel config: # CONFIG_BLK_DEV_UBLK=y # CONFIG_DEBUG_FS=y # CONFIG_FAULT_INJECTION=y # CONFIG_FAULT_INJECTION_DEBUG_FS=y # CONFIG_FAILSLAB=y

echo 10 > /proc/sys/vm/nr_hugepages mkdir -p /tmp/htlb mount -t hugetlbfs none /tmp/htlb fallocate -l 4M /tmp/htlb/ublk_buf

dev_id=$(kublk add -t null --shmem_zc \ --htlb /tmp/htlb/ublk_buf | awk -F '[ :]' '/dev id/ {print $3}')

echo 1 > /sys/kernel/slab/radix_tree_node/failslab echo Y > /sys/kernel/debug/failslab/cache-filter echo Y > /sys/kernel/debug/failslab/ignore-gfp-wait echo 1 > /sys/kernel/debug/failslab/interval echo -1 > /sys/kernel/debug/failslab/times echo 100 > /sys/kernel/debug/failslab/probability

kublk del -n "$dev_id"

On the unfixed kernel the delete command was still running after 3 seconds. Disabling failslab made it return. The fault-injection stack showed:

should_failslab kmem_cache_alloc_lru_noprof __xas_nomem __xa_store xa_store __ublk_shmem_remove_ranges ublk_cdev_rel ublk_ctrl_del_dev

Remove the allocation from the teardown loop. Keep the existing batch limit, but collect {base_pfn, nr_pages} pairs in a fixed-size stack array. Once a matching range is found, the range is erased from the maple tree before dropping the lock, so each successful scan makes progress without depending on any GFP_ATOMIC allocation.

With the same failslab settings, the fixed kernel completed "kublk del -n $dev_id" successfully in about 45 ms.

Which versions are affected by CVE-2026-90181?

How do I fix CVE-2026-90181?

Apply the vendor's patch.

Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.

Is CVE-2026-90181 being exploited?

There is no known exploitation of CVE-2026-90181 in the wild and no public exploit code.

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as DEBIAN-CVE-2026-90181, GHSA-6q49-r2pp-pjwc, UBUNTU-CVE-2026-90181.