inet_diag: fix inet_diag_bc_audit()

A malicious user or buggy application can inject code and trigger an
infinite loop in inet_diag_bc_audit()

Also make sure each instruction is aligned on 4 bytes boundary, to avoid
unaligned accesses.
Reported-by: Dan Rosenberg <drosenberg@vsecurity.com>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/inet_diag.c

@@ -437,7 +437,7 @@ static int valid_cc(const void *bc, int len, int cc)
 			return 0;
 		if (cc == len)
 			return 1;
-		if (op->yes < 4)
+		if (op->yes < 4 || op->yes & 3)
 			return 0;
 		len -= op->yes;
 		bc  += op->yes;
@@ -447,11 +447,11 @@ static int valid_cc(const void *bc, int len, int cc)
 
 static int inet_diag_bc_audit(const void *bytecode, int bytecode_len)
 {
-	const unsigned char *bc = bytecode;
+	const void *bc = bytecode;
 	int  len = bytecode_len;
 
 	while (len > 0) {
-		struct inet_diag_bc_op *op = (struct inet_diag_bc_op *)bc;
+		const struct inet_diag_bc_op *op = bc;
 
 //printk("BC: %d %d %d {%d} / %d\n", op->code, op->yes, op->no, op[1].no, len);
 		switch (op->code) {
@@ -462,22 +462,20 @@ static int inet_diag_bc_audit(const void *bytecode, int bytecode_len)
 		case INET_DIAG_BC_S_LE:
 		case INET_DIAG_BC_D_GE:
 		case INET_DIAG_BC_D_LE:
-			if (op->yes < 4 || op->yes > len + 4)
-				return -EINVAL;
 		case INET_DIAG_BC_JMP:
-			if (op->no < 4 || op->no > len + 4)
+			if (op->no < 4 || op->no > len + 4 || op->no & 3)
 				return -EINVAL;
 			if (op->no < len &&
 			    !valid_cc(bytecode, bytecode_len, len - op->no))
 				return -EINVAL;
 			break;
 		case INET_DIAG_BC_NOP:
-			if (op->yes < 4 || op->yes > len + 4)
-				return -EINVAL;
 			break;
 		default:
 			return -EINVAL;
 		}
+		if (op->yes < 4 || op->yes > len + 4 || op->yes & 3)
+			return -EINVAL;
 		bc  += op->yes;
 		len -= op->yes;
 	}