CVE-2022-50009 in Linux
Summary
by MITRE • 06/18/2025
In the Linux kernel, the following vulnerability has been resolved:
f2fs: fix null-ptr-deref in f2fs_get_dnode_of_data
There is issue as follows when test f2fs atomic write: F2FS-fs (loop0): Can't find valid F2FS filesystem in 2th superblock F2FS-fs (loop0): invalid crc_offset: 0 F2FS-fs (loop0): f2fs_check_nid_range: out-of-range nid=1, run fsck to fix. F2FS-fs (loop0): f2fs_check_nid_range: out-of-range nid=2, run fsck to fix. ================================================================== BUG: KASAN: null-ptr-deref in f2fs_get_dnode_of_data+0xac/0x16d0 Read of size 8 at addr 0000000000000028 by task rep/1990
CPU: 4 PID: 1990 Comm: rep Not tainted 5.19.0-rc6-next-20220715 #266 Call Trace: <TASK> dump_stack_lvl+0x6e/0x91 print_report.cold+0x49a/0x6bb kasan_report+0xa8/0x130 f2fs_get_dnode_of_data+0xac/0x16d0 f2fs_do_write_data_page+0x2a5/0x1030 move_data_page+0x3c5/0xdf0 do_garbage_collect+0x2015/0x36c0 f2fs_gc+0x554/0x1d30 f2fs_balance_fs+0x7f5/0xda0 f2fs_write_single_data_page+0xb66/0xdc0 f2fs_write_cache_pages+0x716/0x1420 f2fs_write_data_pages+0x84f/0x9a0 do_writepages+0x130/0x3a0 filemap_fdatawrite_wbc+0x87/0xa0 file_write_and_wait_range+0x157/0x1c0 f2fs_do_sync_file+0x206/0x12d0 f2fs_sync_file+0x99/0xc0 vfs_fsync_range+0x75/0x140 f2fs_file_write_iter+0xd7b/0x1850 vfs_write+0x645/0x780 ksys_write+0xf1/0x1e0 do_syscall_64+0x3b/0x90 entry_SYSCALL_64_after_hwframe+0x63/0xcd
As 3db1de0e582c commit changed atomic write way which new a cow_inode for atomic write file, and also mark cow_inode as FI_ATOMIC_FILE. When f2fs_do_write_data_page write cow_inode will use cow_inode's cow_inode which is NULL. Then will trigger null-ptr-deref. To solve above issue, introduce FI_COW_FILE flag for COW inode.
Fiexes: 3db1de0e582c("f2fs: change the current atomic write way")
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Analysis
by VulDB Data Team • 11/30/2025
The vulnerability described in CVE-2022-50009 represents a critical null pointer dereference issue within the F2FS (Flash-Friendly File System) implementation in the Linux kernel. This flaw occurs specifically during atomic write operations when the system attempts to access a null pointer in the f2fs_get_dnode_of_data function. The issue manifests when the kernel tries to process data pages for files that have been modified using atomic write mechanisms, leading to a kernel oops and potential system instability. The error trace indicates that the problem originates from a read operation of size 8 at address 0x0000000000000028, which corresponds to a null pointer access during the execution of f2fs_get_dnode_of_data.
The root cause of this vulnerability stems from changes introduced in commit 3db1de0e582c which modified the atomic write implementation in F2FS. This commit introduced a new approach where atomic write operations create a copy-on-write inode (cow_inode) for the file being written to, and marks this cow_inode with the FI_ATOMIC_FILE flag. However, the implementation fails to properly handle cases where the cow_inode's cow_inode field remains NULL during data page write operations. When f2fs_do_write_data_page attempts to process writes to these cow inodes, it incorrectly references the NULL pointer, resulting in the kernel panic. This represents a classic null pointer dereference vulnerability that can be exploited to cause system crashes or potentially more severe consequences depending on the execution context.
The operational impact of this vulnerability is significant for systems utilizing F2FS filesystems, particularly those employing atomic write operations. The vulnerability can lead to complete system crashes during normal file write operations, causing data loss and service interruption. The error messages indicate that the filesystem becomes corrupted and requires manual intervention via fsck to repair. Additionally, the vulnerability affects the kernel's memory management and can potentially be exploited to gain unauthorized access to kernel memory spaces, representing a potential privilege escalation vector. The presence of KASAN (Kernel Address Sanitizer) reporting indicates that this is a well-documented kernel memory safety issue that could be leveraged by attackers to cause system instability or execute arbitrary code in kernel space.
The technical flaw aligns with CWE-476, which describes null pointer dereference vulnerabilities in software systems. This vulnerability also relates to the ATT&CK technique T1068, which involves exploitation of privileges through kernel vulnerabilities. The fix implemented addresses this by introducing a new FI_COW_FILE flag specifically designed to handle copy-on-write inodes properly. This solution ensures that when processing cow inodes, the system properly checks for valid inode references before attempting to access them, preventing the null pointer dereference condition. The fix maintains backward compatibility while addressing the specific edge case that occurs during atomic write operations in F2FS filesystems. The resolution follows best practices for kernel security by implementing proper null checks and flag-based state management for different inode types in the filesystem implementation.