CVE-2024-47736: erofs: handle overlapped pclusters out of crafted images properly
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 pag...
Classification
CVE ID: CVE-2024-47736
Affected Products
Vendor: Linux
Product: Linux
Exploit Prediction Scoring System (EPSS)
EPSS Score: 0.04% (probability of being exploited)
EPSS Percentile: 5.03% (scored less or equal to compared to others)
EPSS Date: 2025-02-15 (when was this score calculated)
References
https://git.kernel.org/stable/c/1bf7e414cac303c9aec1be67872e19be8b64980chttps://git.kernel.org/stable/c/b9b30af0e86ffb485301ecd83b9129c9dfb7ebf8
https://git.kernel.org/stable/c/9cfa199bcbbbba31cbf97b2786f44f4464f3f29a
https://git.kernel.org/stable/c/9e2f9d34dd12e6e5b244ec488bcebd0c2d566c50