CVE-2026-80808: Linux Vulnerability

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.

Affected Software

Source: CNA advisory (CVE.org). NVD analysis pending.

Vendor	Product	Versions
Linux	Linux	>= 1a56cd972ce121b6cf2517a47a578782bbd2ec95, < 119a2f053242ed75bdd2ebc95baf3ae7db6ccacf; >= 1be97463696c7291a3e1547614e96432b0bd3add, < 61631352a5b405c89be579de00903b72e6888aa4; >= 65f8b80053a1b2fd602daa6814e62d6fa90e5e9b, < 8865cd664484517703df5c18a965dc3227572b87; >= 65f8b80053a1b2fd602daa6814e62d6fa90e5e9b, < a40c45268f4358207aa9c53764fed2e05f62986a; >= 65f8b80053a1b2fd602daa6814e62d6fa90e5e9b, < 889ec86464d261f026f6c334040cfc6c58c99d58; >= 65f8b80053a1b2fd602daa6814e62d6fa90e5e9b, < 4902a5cba21aeaf91e6b29e20e0967a5f6abdcd9; >= 65f8b80053a1b2fd602daa6814e62d6fa90e5e9b, < 55ee6533c1db7f7656fa8dd19637f3f8b8c08dc5; >= 65f8b80053a1b2fd602daa6814e62d6fa90e5e9b, < dbd4aea175ad3c46436acb251e817b4374628072; >= 65f8b80053a1b2fd602daa6814e62d6fa90e5e9b, < 54b6bd40898de7906acb2bccc9a96d1b8e6b4323; 98953044b3cdb2cb7d82e7365b659e2ed4f4ca4d; af8ecc8d20e72130771cc076bce7fcf17ccda6c4; c6fac5cf5a5098732623bcd00a8a3eb9f5465144; 96fa141fa295ae9428da73c56c9852053b575c04; >= 5.10.163, < 5.10.267; >= 5.15.61, < 5.15.218; >= 4.19.270, < 4.20; >= 5.4.229, < 5.5; >= 5.18.18, < 5.19; >= 5.19.2, < 5.20
Linux	Linux	6.0

References

Timeline

Published: Sep 4, 2026
Last Modified: Sep 4, 2026
Status: Received

Frequently Asked Questions

What is CVE-2026-80808?

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.

How severe is CVE-2026-80808?

Severity scoring for CVE-2026-80808 is pending analysis.

How do I fix CVE-2026-80808?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

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