EUVD-2026-38886
GHSA-xw4w-5xc6-fwjx
Severity by source
AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Local access and low privilege required to trigger f2fs GC; impact is kernel panic only, with no confidentiality or integrity effect.
Primary rating from NVD.
CVSS VectorNVD
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Lifecycle Timeline
5DescriptionNVD
In the Linux kernel, the following vulnerability has been resolved:
f2fs: avoid reading already updated pages during GC
We found the following issue during fuzz testing:
page: refcount:3 mapcount:0 mapping:00000000b6e89c65 index:0x18b2dc pfn:0x161ba9 memcg:f8ffff800e269c00 aops:f2fs_meta_aops ino:2 flags: 0x52880000000080a9(locked|waiters|uptodate|lru|private|zone=1|kasantag=0x4a) raw: 52880000000080a9 fffffffec6e17588 fffffffec0ccc088 a7ffff8067063618 raw: 000000000018b2dc 0000000000000009 00000003ffffffff f8ffff800e269c00 page dumped because: VM_BUG_ON_FOLIO(folio_test_uptodate(folio)) page_owner tracks the page as allocated post_alloc_hook+0x58c/0x5ec prep_new_page+0x34/0x284 get_page_from_freelist+0x2dcc/0x2e8c __alloc_pages_noprof+0x280/0x76c __folio_alloc_noprof+0x18/0xac __filemap_get_folio+0x6bc/0xdc4 pagecache_get_page+0x3c/0x104 do_garbage_collect+0x5c78/0x77a4 f2fs_gc+0xd74/0x25f0 gc_thread_func+0xb28/0x2930 kthread+0x464/0x5d8 ret_from_fork+0x10/0x20 ------------[ cut here ]------------ kernel BUG at mm/filemap.c:1563! folio_end_read+0x140/0x168 f2fs_finish_read_bio+0x5c4/0xb80 f2fs_read_end_io+0x64c/0x708 bio_endio+0x85c/0x8c0 blk_update_request+0x690/0x127c scsi_end_request+0x9c/0xb8c scsi_io_completion+0xf0/0x250 scsi_finish_command+0x430/0x45c scsi_complete+0x178/0x6d4 blk_mq_complete_request+0xcc/0x104 scsi_done_internal+0x214/0x454 scsi_done+0x24/0x34
which is similar to the problem reported by syzbot: https://syzkaller.appspot.com/bug?extid=3686758660f980b402dc
This case is consistent with the description in commit 9bf1a3f ("f2fs: avoid GC causing encrypted file corrupted"): Page 1 is moved from blkaddr A to blkaddr B by move_data_block, and after being written it is marked as uptodate. Then, Page 1 is moved from blkaddr B to blkaddr C, VM_BUG_ON_FOLIO was triggered in the endio initiated by ra_data_block.
There is no need to read Page 1 again from blkaddr B, since it has already been updated. Therefore, avoid initiating I/O in this case.
AnalysisAI
Kernel panic in the Linux f2fs garbage collector allows a local low-privileged user to crash the system by triggering a VM_BUG_ON_FOLIO assertion when GC attempts to re-read a page already marked uptodate after multiple block relocations. The affected subsystem is f2fs (Flash-Friendly File System); systems using ext4, XFS, or other filesystems are not impacted. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Exploitation requires: (1) the target system must have an f2fs-formatted volume mounted (non-default on most server and desktop Linux; common on Android and embedded flash devices); (2) the GC thread must be active, which occurs automatically under write pressure or can be triggered via the f2fs sysfs interface accessible to low-privileged local users; (3) a data block must be relocated more than once within a GC pass, a condition that arises naturally under heavy fragmentation or during fuzz testing. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | Real-world risk is moderate-to-low. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | A local user on a Linux system with an f2fs-formatted partition creates and modifies files at a rate that drives the GC thread to relocate blocks; with a sufficiently fragmented flash volume, a page may be moved twice in a single GC cycle. When the GC thread's ra_data_block submits I/O on the already-uptodate page, the kernel hits VM_BUG_ON_FOLIO and panics, crashing the system. … |
| Remediation | The primary fix is to upgrade to a patched kernel release: Linux 7.0.10, 6.18.33, or Linux 7.1 (patch 0), which include the upstream stable commits that prevent GC from initiating I/O on already-uptodate pages. … Detailed patch versions, workarounds, and compensating controls in full report. |
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