In the Linux kernel, the following vulnerability has been resolved: net/sched: cls_u32: validate offshift to prevent shift-out-of-bounds u32_change() copies the user-provided tc_u32_sel.offshift (unsigned char, 0-255) into the kernel k…

Overview

In the Linux kernel, the following vulnerability has been resolved:

net/sched: cls_u32: validate offshift to prevent shift-out-of-bounds

u32_change() copies the user-provided tc_u32_sel.offshift (unsigned char, 0-255) into the kernel knode object without bounds validation. When a packet later hits u32_classify() with TC_U32_VAROFFSET set, it evaluates ntohs(offmask & *data) >> offshift where the left operand is a 16-bit value promoted to a 32-bit int. Any offshift >= 32 is undefined behavior per C11 6.5.7p3, triggerable by an unprivileged user via user/network namespaces.

UBSAN: shift-out-of-bounds in net/sched/cls_u32.c:236:43 shift exponent 32 is too large for 32-bit type int

Fix this by rejecting offshift >= 16 during filter creation in u32_change().

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.