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 $dev_id" successfully in about 45 ms.
ublk: avoid teardown retry loop on xarray allocation failure
__ublk_shmem_remove_ranges() removes matching maple tree ranges in
batches, but first stores each range into a temporary xarray so that the
pages can be unpinned after dropping the maple tree lock.
That temporary xarray is filled under the maple tree lock with
xa_store(..., GFP_ATOMIC). If the store fails before mas_erase(), the
current range is left in the tree and the helper returns false. The
outer ublk_shmem_remove_ranges() loop then immediately retries the same
range. While the atomic allocation keeps failing, the teardown path has
no forward progress.
The issue can be reproduced with radix_tree_node failslab injection after
a SHMEM_ZC buffer has already been registered:
# Kernel config:
# CONFIG_BLK_DEV_UBLK=y
# CONFIG_DEBUG_FS=y
# CONFIG_FAULT_INJECTION=y
# CONFIG_FAULT_INJECTION_DEBUG_FS=y
# CONFIG_FAILSLAB=y
echo 10 > /proc/sys/vm/nr_hugepages
mkdir -p /tmp/htlb
mount -t hugetlbfs none /tmp/htlb
fallocate -l 4M /tmp/htlb/ublk_buf
dev_id=$(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 $dev_id" successfully in about 45 ms.
Metrics
Affected Vendors & Products
Advisories
No advisories yet.
Fixes
Solution
No solution given by the vendor.
Workaround
No workaround given by the vendor.
References
History
Thu, 17 Sep 2026 16:30:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Description | In the Linux kernel, the following vulnerability has been resolved: ublk: avoid teardown retry loop on xarray allocation failure __ublk_shmem_remove_ranges() removes matching maple tree ranges in batches, but first stores each range into a temporary xarray so that the pages can be unpinned after dropping the maple tree lock. That temporary xarray is filled under the maple tree lock with xa_store(..., GFP_ATOMIC). If the store fails before mas_erase(), the current range is left in the tree and the helper returns false. The outer ublk_shmem_remove_ranges() loop then immediately retries the same range. While the atomic allocation keeps failing, the teardown path has no forward progress. The issue can be reproduced with radix_tree_node failslab injection after a SHMEM_ZC buffer has already been registered: # Kernel config: # CONFIG_BLK_DEV_UBLK=y # CONFIG_DEBUG_FS=y # CONFIG_FAULT_INJECTION=y # CONFIG_FAULT_INJECTION_DEBUG_FS=y # CONFIG_FAILSLAB=y echo 10 > /proc/sys/vm/nr_hugepages mkdir -p /tmp/htlb mount -t hugetlbfs none /tmp/htlb fallocate -l 4M /tmp/htlb/ublk_buf dev_id=$(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. | |
| Title | ublk: avoid teardown retry loop on xarray allocation failure | |
| First Time appeared |
Linux
Linux linux Kernel |
|
| CPEs | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* | |
| Vendors & Products |
Linux
Linux linux Kernel |
|
| References |
|
Projects
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MITRE
Status: PUBLISHED
Assigner: Linux
Published:
Updated: 2026-09-17T16:07:05.725Z
Reserved: 2026-09-11T19:38:34.791Z
Link: CVE-2026-90181
Vulnrichment
No data.
NVD
Status : Received
Published: 2026-09-17T17:17:12.287
Modified: 2026-09-17T17:17:12.287
Link: CVE-2026-90181
Redhat
No data.
OpenCVE Enrichment
No data.
Weaknesses
No weakness.