CVE-2026-98043bpf: Don't infer non-NULL from a pointer with an unbounded offset

Official description

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().

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/8b414dbe97fcefd116e5a620c3bd9993014aa4ce
• https://git.kernel.org/stable/c/019d845a08b8ccfe8eefaaf4bca6870f2b8c58ae
• https://git.kernel.org/stable/c/65bea674f43c09c0eda033a140dfac6a2842a19f
• https://git.kernel.org/stable/c/cb6642048739bf4ee5aa09fe465511f1e87caa63
• https://git.kernel.org/stable/c/67b529f521a6676cdfc78b91b0217d7eaa84216b