CVE-2022-50730

Vulnerability

Description

CVE-2022-50730 is a bug in the Linux kernel's ext4 filesystem that causes a spurious kernel warning (WARN_ON_ONCE) when evicting an inode that uses the default dioread_nolock mode. The root cause is a race condition between the inode eviction path and a background kworker that converts unwritten extents to written ones. After writeback of newly allocated dirty blocks, the kworker may merge extents and free blocks, which can mark the inode dirty again even though the inode has already been flagged I_FREEING. The warning check in ext4_ext4_evict_inode()` did not account for this specific race scenario.

Exploitation and

Attack Surface

Exploitation requires an attacker to trigger a specific sequence of file operations (e.g., unlinking a file) while the ext4 filesystem is performing writeback with dioreadoread_nolock enabled. No special privileges are needed beyond the ability to create and delete files on an ext4 filesystem. The race window is narrow and involves concurrent execution of the unlink system call and the ext4 end I/O worker.

Impact

The impact is limited to a spurious kernel warning message and a stack trace printed to the kernel log. The developers confirmed that the race does not lead to an inode use-after-free or any memory corruption because ext4_evict_inode() waits for alls` waits for all extent conversions to finish before the warning check. Therefore, the bug is a correctness issue in the warning logic rather than a security vulnerability that could be exploited for privilege escalation or denial of service beyond the warning itself.

Mitigation

The fix removes the WARN_ON_ONCE check that was triggering the false positive. The patch has been applied to the stable kernel branches as referenced in the commit [1] and [2]. Users should update their Linux kernel to a version containing the fix to eliminate the unnecessary warning messages.