CVE-2024-57975 in Linux
Summary
by MITRE • 02/27/2025
In the Linux kernel, the following vulnerability has been resolved:
btrfs: do proper folio cleanup when run_delalloc_nocow() failed
[BUG]
With CONFIG_DEBUG_VM set, test case generic/476 has some chance to crash with the following VM_BUG_ON_FOLIO():
BTRFS error (device dm-3): cow_file_range failed, start 1146880 end 1253375 len 106496 ret -28 BTRFS error (device dm-3): run_delalloc_nocow failed, start 1146880 end 1253375 len 106496 ret -28 page: refcount:4 mapcount:0 mapping:00000000592787cc index:0x12 pfn:0x10664 aops:btrfs_aops [btrfs] ino:101 dentry name(?):"f1774"
flags: 0x2fffff80004028(uptodate|lru|private|node=0|zone=2|lastcpupid=0xfffff) page dumped because: VM_BUG_ON_FOLIO(!folio_test_locked(folio)) ------------[ cut here ]------------
kernel BUG at mm/page-writeback.c:2992! Internal error: Oops - BUG: 00000000f2000800 [#1] SMP
CPU: 2 UID: 0 PID: 3943513 Comm: kworker/u24:15 Tainted: G OE 6.12.0-rc7-custom+ #87 Tainted: [O]=OOT_MODULE, [E]=UNSIGNED_MODULE
Hardware name: QEMU KVM Virtual Machine, BIOS unknown 2/2/2022 Workqueue: events_unbound btrfs_async_reclaim_data_space [btrfs]
pc : folio_clear_dirty_for_io+0x128/0x258 lr : folio_clear_dirty_for_io+0x128/0x258 Call trace: folio_clear_dirty_for_io+0x128/0x258 btrfs_folio_clamp_clear_dirty+0x80/0xd0 [btrfs]
__process_folios_contig+0x154/0x268 [btrfs]
extent_clear_unlock_delalloc+0x5c/0x80 [btrfs]
run_delalloc_nocow+0x5f8/0x760 [btrfs]
btrfs_run_delalloc_range+0xa8/0x220 [btrfs]
writepage_delalloc+0x230/0x4c8 [btrfs]
extent_writepage+0xb8/0x358 [btrfs]
extent_write_cache_pages+0x21c/0x4e8 [btrfs]
btrfs_writepages+0x94/0x150 [btrfs]
do_writepages+0x74/0x190 filemap_fdatawrite_wbc+0x88/0xc8 start_delalloc_inodes+0x178/0x3a8 [btrfs]
btrfs_start_delalloc_roots+0x174/0x280 [btrfs]
shrink_delalloc+0x114/0x280 [btrfs]
flush_space+0x250/0x2f8 [btrfs]
btrfs_async_reclaim_data_space+0x180/0x228 [btrfs]
process_one_work+0x164/0x408 worker_thread+0x25c/0x388 kthread+0x100/0x118 ret_from_fork+0x10/0x20 Code: 910a8021 a90363f7 a9046bf9 94012379 (d4210000) ---[ end trace 0000000000000000 ]---
[CAUSE]
The first two lines of extra debug messages show the problem is caused by the error handling of run_delalloc_nocow().
E.g. we have the following dirtied range (4K blocksize 4K page size):
0 16K 32K |//////////////////////////////////////| | Pre-allocated |
And the range [0, 16K) has a preallocated extent.
- Enter run_delalloc_nocow() for range [0, 16K)
Which found range [0, 16K) is preallocated, can do the proper NOCOW
write.
- Enter fallback_to_fow() for range [16K, 32K)
Since the range [16K, 32K) is not backed by preallocated extent, we
have to go COW.
- cow_file_range() failed for range [16K, 32K)
So cow_file_range() will do the clean up by clearing folio dirty, unlock the folios.
Now the folios in range [16K, 32K) is unlocked.
- Enter extent_clear_unlock_delalloc() from run_delalloc_nocow() Which is called with PAGE_START_WRITEBACK to start page writeback. But folios can only be marked writeback when it's properly locked, thus this triggered the VM_BUG_ON_FOLIO().
Furthermore there is another hidden but common bug that run_delalloc_nocow() is not clearing the folio dirty flags in its error handling path. This is the common bug shared between run_delalloc_nocow() and cow_file_range().
[FIX]
- Clear folio dirty for range [@start, @cur_offset)
Introduce a helper, cleanup_dirty_folios(), which will find and lock the folio in the range, clear the dirty flag and start/end the writeback, with the extra handling for the @locked_folio.
- Introduce a helper to clear folio dirty, start and end writeback
- Introduce a helper to record the last failed COW range end This is to trace which range we should skip, to avoid double unlocking.
- Skip the failed COW range for the e ---truncated---
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Analysis
by VulDB Data Team • 05/24/2026
The vulnerability described in CVE-2024-57975 affects the Linux kernel's btrfs file system implementation, specifically within the delalloc (delayed allocation) handling mechanism. This issue manifests as a kernel panic or system crash when the kernel attempts to clean up folios during error conditions in the run_delalloc_nocow() function. The problem occurs under specific debugging configurations with CONFIG_DEBUG_VM enabled, making it particularly relevant for developers and system administrators who rely on kernel debugging features. The vulnerability directly impacts the stability and reliability of systems using btrfs file systems, especially those under heavy I/O workloads where delalloc operations are frequently invoked.
The technical flaw stems from improper error handling within the btrfs kernel module's memory management routines. When run_delalloc_nocow() encounters a failure during the cow_file_range() operation, it fails to properly clean up folio states, leaving them in an inconsistent condition. The core issue involves a race condition or improper state management where folios that have been unlocked during the error recovery phase are subsequently subjected to writeback operations without proper locking. This violation of kernel memory management principles triggers the VM_BUG_ON_FOLIO() macro, which is designed to catch such critical inconsistencies in the virtual memory subsystem. The vulnerability is classified as a memory corruption issue that can lead to kernel oops and system crashes, representing a direct violation of kernel safety mechanisms.
The operational impact of this vulnerability extends beyond simple system instability to potentially compromise data integrity and availability in production environments. Systems running btrfs file systems with active delalloc operations are at risk of experiencing unexpected kernel panics, particularly during write operations that span across preallocated and non-preallocated extents. The crash pattern described indicates that the issue occurs during asynchronous data space reclaim operations, suggesting that even routine system maintenance tasks could trigger the vulnerability. This makes the vulnerability particularly dangerous in enterprise environments where continuous system uptime is critical, as it could lead to unplanned outages and data loss scenarios. The vulnerability also affects the broader Linux ecosystem since btrfs is widely used in various distributions and storage solutions.
Mitigation strategies for this vulnerability should focus on immediate kernel updates to versions containing the patched code, as the fix involves comprehensive cleanup of folio state management during error conditions. The patch introduces dedicated helper functions to properly manage folio dirty flags and writeback operations, ensuring that folios are correctly locked and unlocked during error recovery paths. Additionally, system administrators should consider implementing monitoring solutions to detect early signs of memory corruption or kernel panics related to btrfs operations. The fix addresses the underlying CWE-129 issue related to improper handling of memory objects and aligns with ATT&CK tactics involving privilege escalation and system stability compromise. Organizations should also review their backup and recovery procedures to ensure data integrity can be maintained in case of system crashes, as the vulnerability could potentially be exploited to cause denial of service or data corruption in targeted environments.