bpf: Fix overflow of jump offset in constant blinding

In the Linux kernel, the following vulnerability has been resolved: bpf: Fix overflow of jump offset in constant blinding bpf_jit_blind_insn() rewrites 'if rX op imm goto off' into: AX = imm ^ rnd AX ^= rnd if rX op AX goto off and subtracts 2 from off when the jump is backward. off is s16, so -32767 and -32768 wrap and the jump goes 32767 insns forward, past the end of the prog. The jump is inside the patch, hence bpf_adj_branches() doesn't check it. The kernel crashes when such prog runs with bpf_jit_harden=2. Return -ERANGE in such case. bpf_jit_blind_constants() fails the same way when blinding of other insns moves a jump out of range.