CVE-2026-98043

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

bpf: Don't infer non-NULL from a pointer with an unbounded offset

reg_not_null() decides that a register holds a non-NULL value by

looking at its type alone. For pointer types that allow arithmetic the

type only guarantees a non-NULL base, in case of an unbound offset

the runtime offset value might still add up to NULL.

Consider the followng program:

r6 = bpf_map_lookup_elem(map, &0); /* present */

if (r6 == 0) return 0;

r7 = bpf_map_lookup_elem(map, &1); /* absent, NULL at runtime */

r8 = r7;

r8 -= r6; /* pointer - pointer: unknown scalar, -r6 */

r8 <<= 1;

r8 >>= 1; /* any non-negative offset is accepted by */

/* check_reg_sane_offset_ptr() */

r6 += r8; /* verifier: map value; runtime: zero */

if (r7 != r6) return 0;

*(u8 *)(r7 + 0); /* r7 is inferred non-NULL, both are zero */

At runtime both registers are zero, the comparison is true and the

load faults with NULL pointer dereference.

Require the offset to be within +-BPF_MAX_VAR_OFF in reg_not_null().