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

First published: Mon Oct 21 2024(Updated: )

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.

Credit: 416baaa9-dc9f-4396-8d5f-8c081fb06d67

Never miss a vulnerability like this again

Sign up to SecAlerts for real-time vulnerability data matched to your software, aggregated from hundreds of sources.

Read MoreStart Free Trial

• agent/title
• agent/type
• agent/description
• agent/first-publish-date
• agent/author
• agent/event
• agent/severity
• agent/remedy
• agent/weakness
• collector/mitre-cve
• source/MITRE
• agent/references
• agent/last-modified-date
• agent/source
• collector/nvd-api
• source/NVD
• agent/software-canonical-lookup
• agent/software-canonical-lookup-request
• agent/softwarecombine
• agent/tags
• collector/usn-cve
• source/Ubuntu
• collector/launchpad-cve
• source/Launchpad
• collector/security-tracker-debian
• source/Debian
• vendor/linux
• canonical/linux kernel
• version/linux kernel/5.13
• version/linux kernel/6.11
• package-manager/debian