Linux Kernel Undefined Behavior Vulnerability in ext4 Bit Shift Operation

A vulnerability in the Linux kernel's ext4 file system has been addressed, which involved undefined behavior due to shifting a signed 32-bit value by 31 bits. This issue was resolved by changing the significant bit to unsigned. The vulnerability triggered a 'shift-out-of-bounds' warning from Undefined Behavior Sanitizer (UBSAN), indicating that the left shift operation could not be represented within the 'int' data type. This vulnerability affects several versions of the Linux kernel.

Impact

Exploitation of this vulnerability could lead to undefined behavior in the kernel, potentially causing instability or unexpected behavior in the system.

Reproduction

The vulnerability can be reproduced by initializing the ext4 file system in a version of the Linux kernel that is affected by this issue. During the initialization process, the undefined behavior in the bit shift operation will trigger a UBSAN warning, indicating that a shift operation has gone out of bounds. This warning can be seen in the call trace, which shows the sequence of function calls leading up to the warning.

Remediation

Users can upgrade to the latest version of the Linux kernel where this vulnerability has been fixed.