Linux Kernel f2fs Filesystem Read COW Data from Original Inode During Atomic Write Vulnerability

A vulnerability in the Linux kernel's f2fs filesystem allows for a general protection fault due to improper handling of copy-on-write (COW) data during atomic write operations. When an atomic-write file is updated, the f2fs_write_begin() function may inadvertently read data from the COW inode using the original inode's encryption context. This issue arises because the COW inode, created as a temporary file, inherits an encryption policy that can differ from that of pre-existing files. As a result, the decryption process may encounter a null pointer, leading to a crash. The vulnerability affects the Linux kernel's stable branch.

Impact

Exploitation of this vulnerability causes a general protection fault, likely due to a null pointer dereference, disrupting kernel operations and potentially leading to a system crash.

Reproduction

To reproduce this vulnerability, create a file in the f2fs filesystem and apply an encryption policy. Then, initiate an atomic write operation on the file. The f2fs_write_begin() function will read from the COW inode, but the decryption process will fail, causing a null pointer dereference and a general protection fault.

Remediation

The vulnerability has been addressed in the Linux kernel. Users should upgrade to the latest version.