bpf: reset id on CONST_IMM transition

Whenever we set the register to the type CONST_IMM, we currently don't
reset the id to 0. id member is not used in CONST_IMM case, so don't
let it become stale, where pruning won't be able to match later on.
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>
Acked-by: NAlexei Starovoitov <ast@kernel.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

kernel/bpf/verifier.c

@@ -1952,6 +1952,7 @@ static int check_alu_op(struct bpf_verifier_env *env, struct bpf_insn *insn)
 			 */
 			regs[insn->dst_reg].type = CONST_IMM;
 			regs[insn->dst_reg].imm = insn->imm;
+			regs[insn->dst_reg].id = 0;
 			regs[insn->dst_reg].max_value = insn->imm;
 			regs[insn->dst_reg].min_value = insn->imm;
 			regs[insn->dst_reg].min_align = calc_align(insn->imm);
@@ -2409,6 +2410,7 @@ static int check_ld_imm(struct bpf_verifier_env *env, struct bpf_insn *insn)
 
 		regs[insn->dst_reg].type = CONST_IMM;
 		regs[insn->dst_reg].imm = imm;
+		regs[insn->dst_reg].id = 0;
 		return 0;
 	}