CVE-2026-80808
ext4: stop retrying saturated xattr cache entries
Published Sep 4, 2026
CVSS n/a
EPSS < 1%
KEV · Not listed
Description
In the Linux kernel, the following vulnerability has been resolved:
ext4: stop retrying saturated xattr cache entries
ext4_xattr_block_set() retries when a cache entry selected for reuse
has a saturated reference count after taking the buffer lock. The retry
returns to the mbcache lookup without making that entry ineligible, so
it can select the same unusable entry indefinitely. A task spinning
there can hold the parent directory's i_rwsem and leave concurrent
rmdir callers blocked.
Normally a reusable entry has a reference count below
EXT4_XATTR_REFCOUNT_MAX because the count and MBE_REUSABLE_B are
updated under the same buffer lock. A corrupted filesystem can violate
that invariant. The syzbot reproducer reports allocator and xattr
corruption before triggering this retry loop.
Check the untrusted on-disk count before incrementing it, avoiding
overflow, and clear MBE_REUSABLE_B when it is already saturated. The
next lookup then skips the entry that was just proven unusable. This
mirrors the normal transition at EXT4_XATTR_REFCOUNT_MAX; the release
path marks the entry reusable again on the exact 1024-to-1023
transition.
Using the same QEMU harness and guest parameters, current unpatched
Linux hung in 6 of 8 420-second trials with the do_rmdir signature;
representative NMI backtraces caught the owner spinning in
ext4_xattr_block_set(). The patched kernel completed 28 of 28 trials
without a hung-task report; the final twelve trials exercised the
reviewed overflow-safe form of the change. syzbot's patch testing also
completed without reproducing the hang.
ext4: stop retrying saturated xattr cache entries
ext4_xattr_block_set() retries when a cache entry selected for reuse
has a saturated reference count after taking the buffer lock. The retry
returns to the mbcache lookup without making that entry ineligible, so
it can select the same unusable entry indefinitely. A task spinning
there can hold the parent directory's i_rwsem and leave concurrent
rmdir callers blocked.
Normally a reusable entry has a reference count below
EXT4_XATTR_REFCOUNT_MAX because the count and MBE_REUSABLE_B are
updated under the same buffer lock. A corrupted filesystem can violate
that invariant. The syzbot reproducer reports allocator and xattr
corruption before triggering this retry loop.
Check the untrusted on-disk count before incrementing it, avoiding
overflow, and clear MBE_REUSABLE_B when it is already saturated. The
next lookup then skips the entry that was just proven unusable. This
mirrors the normal transition at EXT4_XATTR_REFCOUNT_MAX; the release
path marks the entry reusable again on the exact 1024-to-1023
transition.
Using the same QEMU harness and guest parameters, current unpatched
Linux hung in 6 of 8 420-second trials with the do_rmdir signature;
representative NMI backtraces caught the owner spinning in
ext4_xattr_block_set(). The patched kernel completed 28 of 28 trials
without a hung-task report; the final twelve trials exercised the
reviewed overflow-safe form of the change. syzbot's patch testing also
completed without reproducing the hang.
Affected Products
-
CVE record
-
NVD configurations
No data
-
Red Hat packages
No data
-
OpenCVE enrichment
Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).
| Vendor | Product | Default status | Versions | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Linux | Linux | unaffected |
|
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| Linux | Linux | affected |
|
No data.
No data.
| Vendor | Product | Versions | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Linux | Linux Kernel |
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| Linux | Linux Kernel |
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Remediation
Tracking
Advisories
| Source | ID | Title |
|---|---|---|
 Debian DLA |
DLA-4777-1 | linux security update |
| Debian DLA |
DLA-4788-1 | linux-6.12 security update |
 Ubuntu USN |
USN-8961-1 | Linux kernel vulnerabilities |
| Ubuntu USN |
USN-9019-1 | Linux kernel (Azure) vulnerabilities |
| Ubuntu USN |
USN-9020-1 | Linux kernel vulnerabilities |
| Ubuntu USN |
USN-9022-1 | Linux kernel vulnerabilities |
| Ubuntu USN |
USN-9023-1 | Linux kernel vulnerabilities |
| Ubuntu USN |
USN-9024-1 | Linux kernel vulnerabilities |
| Ubuntu USN |
USN-9025-1 | Linux kernel vulnerabilities |
| Ubuntu USN |
USN-9026-1 | Linux kernel (Azure) vulnerabilities |
| Ubuntu USN |
USN-9029-1 | Linux kernel (Raspberry Pi) vulnerabilities |
| Ubuntu USN |
USN-9039-1 | Linux kernel (Azure CVM) vulnerabilities |
| Ubuntu USN |
USN-9040-1 | Linux kernel (Low Latency NVIDIA) vulnerabilities |
| Ubuntu USN |
USN-9066-1 | Linux kernel (HWE) vulnerabilities |
| Ubuntu USN |
USN-9091-1 | Linux kernel (NVIDIA Tegra) vulnerabilities |
Metrics
No CVSS v4.0
No CVSS v3.1
No CVSS v3.0
No CVSS v2
This CVE is not in the KEV list.
Exploit prediction score: < 1% (0.195% probability within 30 days)
Exploitation none
Automatable no
Technical Impact partial
References
History
Nov 7, 2026 7:30 AM
Scoring metrics updated
View changes
| Type | Values Removed | Values Added |
|---|---|---|
| Metrics |
ssvc
|
Sep 4, 2026 9:45 PM
Weaknesses updated
View changes
| Type | Values Removed | Values Added |
|---|---|---|
| Weaknesses | CWE-665 |
Sep 4, 2026 3:30 PM
Description updated. Title updated. First appearance in the feed. Affected versions updated. Affected vendors updated. Added references
View changes
| Type | Values Removed | Values Added |
|---|---|---|
| Description | In the Linux kernel, the following vulnerability has been resolved: ext4: stop retrying saturated xattr cache entries ext4_xattr_block_set() retries when a cache entry selected for reuse has a saturated reference count after taking the buffer lock. The retry returns to the mbcache lookup without making that entry ineligible, so it can select the same unusable entry indefinitely. A task spinning there can hold the parent directory's i_rwsem and leave concurrent rmdir callers blocked. Normally a reusable entry has a reference count below EXT4_XATTR_REFCOUNT_MAX because the count and MBE_REUSABLE_B are updated under the same buffer lock. A corrupted filesystem can violate that invariant. The syzbot reproducer reports allocator and xattr corruption before triggering this retry loop. Check the untrusted on-disk count before incrementing it, avoiding overflow, and clear MBE_REUSABLE_B when it is already saturated. The next lookup then skips the entry that was just proven unusable. This mirrors the normal transition at EXT4_XATTR_REFCOUNT_MAX; the release path marks the entry reusable again on the exact 1024-to-1023 transition. Using the same QEMU harness and guest parameters, current unpatched Linux hung in 6 of 8 420-second trials with the do_rmdir signature; representative NMI backtraces caught the owner spinning in ext4_xattr_block_set(). The patched kernel completed 28 of 28 trials without a hung-task report; the final twelve trials exercised the reviewed overflow-safe form of the change. syzbot's patch testing also completed without reproducing the hang. | |
| Title | ext4: stop retrying saturated xattr cache entries | |
| First Time appeared |
Linux
Linux linux Kernel |
|
| CPEs | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* | |
| Vendors & Products |
Linux
Linux linux Kernel |
|
| References |
|
|
Subscriptions
Weaknesses
