Linux Kernel ext4 Inline Data Handling Vulnerability Leading to Kernel Panic

A vulnerability in the Linux kernel's ext4 file system has been identified, related to the management of inline data. Under certain conditions, the kernel can encounter a bug that leads to a crash. This issue arises when inline data is converted to extent format, but the conversion process is not properly synchronized with the file system's write operations. As a result, a kernel bug is triggered, indicating an invalid operation, and the system may become unstable.

Impact

Exploitation of this vulnerability causes a kernel panic, abruptly terminating all processes and potentially leading to data loss.

Reproduction

The vulnerability can be reproduced by writing inline data to an inode using the VFS write operation. If the inline data size is too small, the file system will allocate a block for writing, leaving the mapping with a dirty page. Following this, the 'fallocate' command can be used to preallocate space, which triggers the conversion of inline data to extent format. If this process is not properly managed, the 'writepages' operation can cause a kernel bug due to the inconsistent state of the inode.