CVE-2025-40138
Unknown Unknown - Not Provided
BaseFortify

Publication date: 2025-11-12

Last updated on: 2025-11-12

Assigner: kernel.org

Description
In the Linux kernel, the following vulnerability has been resolved: f2fs: fix to avoid NULL pointer dereference in f2fs_check_quota_consistency() syzbot reported a f2fs bug as below: Oops: gen[ 107.736417][ T5848] Oops: general protection fault, probably for non-canonical address 0xdffffc0000000000: 0000 [#1] SMP KASAN PTI KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007] CPU: 1 UID: 0 PID: 5848 Comm: syz-executor263 Tainted: G W 6.17.0-rc1-syzkaller-00014-g0e39a731820a #0 PREEMPT_{RT,(full)} RIP: 0010:strcmp+0x3c/0xc0 lib/string.c:284 Call Trace: <TASK> f2fs_check_quota_consistency fs/f2fs/super.c:1188 [inline] f2fs_check_opt_consistency+0x1378/0x2c10 fs/f2fs/super.c:1436 __f2fs_remount fs/f2fs/super.c:2653 [inline] f2fs_reconfigure+0x482/0x1770 fs/f2fs/super.c:5297 reconfigure_super+0x224/0x890 fs/super.c:1077 do_remount fs/namespace.c:3314 [inline] path_mount+0xd18/0xfe0 fs/namespace.c:4112 do_mount fs/namespace.c:4133 [inline] __do_sys_mount fs/namespace.c:4344 [inline] __se_sys_mount+0x317/0x410 fs/namespace.c:4321 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f The direct reason is f2fs_check_quota_consistency() may suffer null-ptr-deref issue in strcmp(). The bug can be reproduced w/ below scripts: mkfs.f2fs -f /dev/vdb mount -t f2fs -o usrquota /dev/vdb /mnt/f2fs quotacheck -uc /mnt/f2fs/ umount /mnt/f2fs mount -t f2fs -o usrjquota=aquota.user,jqfmt=vfsold /dev/vdb /mnt/f2fs mount -t f2fs -o remount,usrjquota=,jqfmt=vfsold /dev/vdb /mnt/f2fs umount /mnt/f2fs So, before old_qname and new_qname comparison, we need to check whether they are all valid pointers, fix it.
CVSS Scores
EPSS Scores
Probability:
Percentile:
Meta Information
Published
2025-11-12
Last Modified
2025-11-12
Generated
2026-05-07
AI Q&A
2025-11-13
EPSS Evaluated
2026-05-05
NVD
CVE-2025-40138
Affected Vendors & Products
Showing 1 associated CPE
Vendor Product Version / Range
linux linux_kernel 6.17.0-rc1
Helpful Resources
Exploitability
CWE
CWE Icon
KEV
KEV Icon
CWE ID Description
CWE-UNKNOWN
Attack-Flow Graph
AI Powered Q&A
Can you explain this vulnerability to me?

This vulnerability is a NULL pointer dereference in the Linux kernel's f2fs filesystem code, specifically in the function f2fs_check_quota_consistency(). It occurs because the code compares two quota name pointers (old_qname and new_qname) without verifying if they are valid, leading to a crash (general protection fault) when strcmp() is called on a NULL pointer.


How can this vulnerability impact me? :

This vulnerability can cause a system crash (kernel oops) when mounting or remounting an f2fs filesystem with quota options, potentially leading to denial of service by making the system unstable or unresponsive during these operations.


How can this vulnerability be detected on my network or system? Can you suggest some commands?

This vulnerability can be detected by reproducing the conditions that trigger the null pointer dereference in the f2fs_check_quota_consistency() function. The following commands can be used to test for the issue on a system with an f2fs filesystem and a block device (e.g., /dev/vdb): mkfs.f2fs -f /dev/vdb mount -t f2fs -o usrquota /dev/vdb /mnt/f2fs quotacheck -uc /mnt/f2fs/ umount /mnt/f2fs mount -t f2fs -o usrjquota=aquota.user,jqfmt=vfsold /dev/vdb /mnt/f2fs mount -t f2fs -o remount,usrjquota=,jqfmt=vfsold /dev/vdb /mnt/f2fs umount /mnt/f2fs If these commands cause a kernel oops or crash related to a null pointer dereference, the vulnerability is present.


What immediate steps should I take to mitigate this vulnerability?

Immediate mitigation involves applying the patch that fixes the null pointer dereference in f2fs_check_quota_consistency() by ensuring that pointers old_qname and new_qname are validated before comparison. Until the patch is applied, avoid mounting f2fs filesystems with quota options that trigger the vulnerable code paths, such as usrquota or usrjquota options. Monitoring for kernel oops related to f2fs quota consistency checks and avoiding quota operations on f2fs filesystems can reduce risk.


Ask Our AI Assistant
Need more information? Ask your question to get an AI reply (Powered by our expertise)
0/70
EPSS Chart