CVE-2025-38164 in Linux
Summary
by MITRE • 07/03/2025
In the Linux kernel, the following vulnerability has been resolved:
f2fs: zone: fix to avoid inconsistence in between SIT and SSA
w/ below testcase, it will cause inconsistence in between SIT and SSA.
create_null_blk 512 2 1024 1024 mkfs.f2fs -m /dev/nullb0 mount /dev/nullb0 /mnt/f2fs/ touch /mnt/f2fs/file f2fs_io pinfile set /mnt/f2fs/file fallocate -l 4GiB /mnt/f2fs/file
F2FS-fs (nullb0): Inconsistent segment (0) type [1, 0] in SSA and SIT
CPU: 5 UID: 0 PID: 2398 Comm: fallocate Tainted: G O 6.13.0-rc1 #84 Tainted: [O]=OOT_MODULE
Hardware name: innotek GmbH VirtualBox/VirtualBox, BIOS VirtualBox 12/01/2006 Call Trace: <TASK> dump_stack_lvl+0xb3/0xd0 dump_stack+0x14/0x20 f2fs_handle_critical_error+0x18c/0x220 [f2fs]
f2fs_stop_checkpoint+0x38/0x50 [f2fs]
do_garbage_collect+0x674/0x6e0 [f2fs]
f2fs_gc_range+0x12b/0x230 [f2fs]
f2fs_allocate_pinning_section+0x5c/0x150 [f2fs]
f2fs_expand_inode_data+0x1cc/0x3c0 [f2fs]
f2fs_fallocate+0x3c3/0x410 [f2fs]
vfs_fallocate+0x15f/0x4b0 __x64_sys_fallocate+0x4a/0x80 x64_sys_call+0x15e8/0x1b80 do_syscall_64+0x68/0x130 entry_SYSCALL_64_after_hwframe+0x67/0x6f RIP: 0033:0x7f9dba5197ca F2FS-fs (nullb0): Stopped filesystem due to reason: 4
The reason is f2fs_gc_range() may try to migrate block in curseg, however, its SSA block is not uptodate due to the last summary block data is still in cache of curseg.
In this patch, we add a condition in f2fs_gc_range() to check whether section is opened or not, and skip block migration for opened section.
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Analysis
by VulDB Data Team • 07/31/2026
This vulnerability exists within the F2FS (Flash-Friendly File System) implementation in the Linux kernel, specifically addressing inconsistencies between the Segment Information Table (SIT) and the Segment Summary Area (SSA). The flaw manifests when the f2fs_gc_range() function attempts to migrate blocks from the current segment while the corresponding SSA block remains stale due to cached data in the current segment's summary block. This condition creates a critical inconsistency where the SIT and SSA maintain conflicting information about segment types, leading to filesystem corruption and potential system instability.
The technical root cause stems from improper synchronization between the segment management structures in F2FS. When f2fs_gc_range() is invoked during block allocation operations, it attempts to migrate blocks from the current segment without verifying whether the segment's summary information is up-to-date. The current segment maintains cached summary data that hasn't been flushed to the SSA, creating a temporal inconsistency where the SIT reflects one state while the SSA contains outdated information. This discrepancy triggers the kernel's critical error handling mechanism, resulting in filesystem shutdown to prevent further corruption.
The operational impact of this vulnerability extends beyond simple filesystem corruption to potentially compromise system stability and data integrity. The vulnerability can be triggered through standard file system operations involving large file allocations and pinning mechanisms, making it particularly dangerous in production environments where continuous file system operations occur. The error manifests as a kernel panic with the specific message indicating inconsistent segment types between SIT and SSA, accompanied by a stack trace showing the call path through the garbage collection and allocation functions. According to CWE classification, this represents a CWE-129: Improper Validation of Array Index vulnerability, as the inconsistency arises from improper validation of segment state information during critical file system operations.
The attack scenario involves executing a sequence of file system operations that force the kernel into a state where stale segment information can cause the critical inconsistency. The test case demonstrates this through creating a null block device, formatting it with F2FS, mounting it, creating a file, pinning it, and then performing a large file allocation that triggers the garbage collection path. This sequence exploits the timing window where segment summary data is cached but not yet committed to the SSA, creating the conditions necessary for the inconsistency to occur. The vulnerability aligns with ATT&CK technique T1490: Inhibit System Recovery, as it can cause filesystem shutdown and potential data loss through improper error handling.
Mitigation strategies should focus on ensuring proper synchronization between segment summary information and the SIT structures. The patch addresses this by adding a condition check in f2fs_gc_range() to verify whether a section is opened before attempting block migration. This prevents migration operations on segments with stale summary data, ensuring that only properly committed segment information is used during garbage collection. System administrators should ensure their kernels are updated with the patched version to prevent exploitation, while monitoring for filesystem errors related to segment consistency. The fix represents a defensive programming approach that prevents the problematic code path rather than attempting to resolve the inconsistency after it occurs, aligning with security best practices for preventing critical system errors.