CVE-2026-98040

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

bpf: Mark the zero register precise for a register-form NULL check

check_cond_jmp_op() accepts "if rA <op> rB" as a NULL check for a

nullable pointer rA when rB is a scalar known to be zero,

lifts PTR_MAYBE_NULL from rA in the corresponding branch and does not

mark rB precise. Consider the following program:

r0 = bpf_get_prandom_u32();

r6 = 1; /* the r6 == 0 path is explored first */

if (r0 == 0) goto 1f;

r6 = 0;

1:

r0 = bpf_map_lookup_elem(map, &0); /* absent, NULL at runtime */

if (r0 == r6) goto 2f; /* taken as a NULL check for r0 */

*(u8 *)(r0 + 0); /* verifier: map value; runtime: zero */

2:

return 0;

The r6 == 0 path is explored first and the dereference is accepted.

The r6 == 1 path is pruned at the checkpoint recorded for (1),

so the comparison is never verified with a non-zero r6. At runtime a

failed lookup returns NULL, NULL != 1 takes the non-NULL edge and the

program dereferences a pointer that is zero.