CVE-2024-47736 Information

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 (rofs: tidy up struct z_erofs_bvec) for simplicity although it shouldn’t be any difference.

CVSS Vector

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Reference

https://git.kernel.org/stable/c/b9b30af0e86ffb485301ecd83b9129c9dfb7ebf8 https://git.kernel.org/stable/c/9cfa199bcbbbba31cbf97b2786f44f4464f3f29a https://git.kernel.org/stable/c/9e2f9d34dd12e6e5b244ec488bcebd0c2d566c50

Attack Complexity

LOW

Privileges Required

LOW

User Interaction Required

LOW

Scope

NONE

Confidentiality Impact

UNCHANGED

Integrity Impact

NONE

Availability Impact

NONE

Base Score

HIGH

Base Severity

5.5