CVE-2024-49859: Linux Kernel F2FS Atomic Write Race Condition Resolution and Exploit Details

Recently, in the Linux kernel, a critical vulnerability CVE-2024-49859 has been resolved. This vulnerability specifically affects the f2fs (Flash-Friendly File System) ioctl interfaces. The absence of atomic_write checks in certain f2fs ioctl operations may lead to a potential race condition problem. In this post, we will discuss the details of this vulnerability, relevant code snippets, and the necessary steps needed to address this issue.

Vulnerability Description

The f2fs (Flash-Friendly File System) is a modern file system designed specifically for NAND-based storage devices such as Solid State Drives (SSDs), eMMC, UFS, and SD cards. Among its many features, f2fs supports file pinning and file defragmentation using its ioctl interfaces. The three operations involved in this vulnerability are f2fs_ioc_set_pin_file(), f2fs_move_file_range(), and f2fs_defragment_range(). These ioctl interfaces missed atomic_write checks, potentially leading to race conditions.

Exploit Details

As described above, the absence of atomic_write checks in f2fs_ioc_set_pin_file(), f2fs_move_file_range(), and f2fs_defragment_range() may cause race conditions. This vulnerability may eventually result in unfortunate incidents like data corruption, storage failure, or even loss of critical data stored in the f2fs file system.

The following code snippet demonstrates the missing atomic_file check in these operations

// Before fix
int f2fs_ioc_set_pin_file(struct file *filp, unsigned long arg){
    ...
    // Missing atomic_file check here
}

To fix this vulnerability, Linux Kernel developers proposed a patch to add the missing atomic_file checks in these ioctl interfaces. The following code snippet shows the correct implementation after the fix:

// After fix
int f2fs_ioc_set_pin_file(struct file *filp, unsigned long arg){
    ...
    // Adding atomic_file check
    if (!file_check_policy_atomic(filp, F2FS_IO_ATOMIC_REQUEST))
        return -EFAULT;
}

Original References

The vulnerability information was originally reported in the Linux kernel mailing list by Yunlei He, as well as the vulnerability fix. You can find the original patch and discussion in these links:
1. Patch 1/2: Add atomic_file checks in f2fs_ioc_set_pin_file()
2. Patch 2/2: Add atomic_file checks in f2fs_move_file_range() and f2fs_defragment_range()

Conclusion

CVE-2024-49859 is a serious vulnerability affecting the Linux kernel's f2fs ioctl interfaces. By addressing the missing atomic_file checks, this issue has been successfully resolved. Users and developers with systems running on f2fs are recommended to update their kernel to the latest version, including the patch for this vulnerability. Additional research on load_ctl and f2fs is an ongoing effort to reassure the security and stability of the Linux file system.

For further information on the f2fs, you can visit the official Linux Kernel Documentation.

Timeline

Published on: 10/21/2024 13:15:06 UTC
Last modified on: 10/22/2024 16:13:03 UTC