bpf/verifier: relax MUL range computation check

MUL instruction required that src_reg would be a known value (i.e.
src_reg would be a const value). The condition in this case can be
relaxed, since the range computation algorithm used in current code
already supports a proper range computation for any valid range value on
its operands.

Signed-off-by: Cupertino Miranda <cupertino.miranda@oracle.com>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Acked-by: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Cc: Yonghong Song <yonghong.song@linux.dev>
Cc: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: David Faust <david.faust@oracle.com>
Cc: Jose Marchesi <jose.marchesi@oracle.com>
Cc: Elena Zannoni <elena.zannoni@oracle.com>
Link: https://lore.kernel.org/r/20240506141849.185293-6-cupertino.miranda@oracle.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Author: cupermir

kernel/bpf/verifier.c

@@ -13902,12 +13902,8 @@ static bool is_safe_to_compute_dst_reg_range(struct bpf_insn *insn,
 	case BPF_AND:
 	case BPF_XOR:
 	case BPF_OR:
-		return true;
-
-	/* Compute range for the following only if the src_reg is const.
-	 */
 	case BPF_MUL:
-		return src_is_const;
+		return true;
 
 	/* Shift operators range is only computable if shift dimension operand
 	 * is a constant. Shifts greater than 31 or 63 are undefined. This