CVE-2024-47736

Summary

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.

Affected Software

VendorProductVersion RangeStatus
LinuxLinux8e6c8fa9f2e95c88a642521a5da19a8e31748846 < c1172e65aad4b115392ea4c6e61e56e5b9b69df4affected
LinuxLinux8e6c8fa9f2e95c88a642521a5da19a8e31748846 < 1bf7e414cac303c9aec1be67872e19be8b64980caffected
LinuxLinux8e6c8fa9f2e95c88a642521a5da19a8e31748846 < b9b30af0e86ffb485301ecd83b9129c9dfb7ebf8affected
LinuxLinux8e6c8fa9f2e95c88a642521a5da19a8e31748846 < 9cfa199bcbbbba31cbf97b2786f44f4464f3f29aaffected
LinuxLinux8e6c8fa9f2e95c88a642521a5da19a8e31748846 < 9e2f9d34dd12e6e5b244ec488bcebd0c2d566c50affected
LinuxLinux5.13affected
LinuxLinux0 < 5.13unaffected
LinuxLinux6.1.168 <= 6.1.*unaffected
LinuxLinux6.6.72 <= 6.6.*unaffected
LinuxLinux6.10.13 <= 6.10.*unaffected
LinuxLinux6.11.2 <= 6.11.*unaffected
LinuxLinux6.12 <= *unaffected

Weaknesses

ADP Enrichment

CISA ADP Vulnrichment

  • SSVC:
  • Exploitation: none
    • Automatable: no
    • Technical Impact: partial

References