CVE-2026-74544net/sched: cls_u32: validate offshift to prevent shift-out-of-bounds

Official description

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().

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/7fd5b2287e5cf33e114fb7f0cef781a546039757
• https://git.kernel.org/stable/c/724c8edbacf1259988829cb9967f751222121d8a
• https://git.kernel.org/stable/c/006a4598da9a6b02e0ddc3ca5042b97224774364
• https://git.kernel.org/stable/c/9990cac513e8b191de2ee589051ea7ebf3cee940
• https://git.kernel.org/stable/c/313cb9ffc4101a885d791facf4b5ea3d5e06144d
• https://git.kernel.org/stable/c/aef96eead2860cbfa371e4471d4f04412213b958