Avoid undefined behaviour with the ctype(3) functions.

As defined in the C standard:

	In all cases the argument is an int, the value of which shall
	be representable as an unsigned char or shall equal the value
	of the macro EOF.  If the argument has any other value, the
	behavior is undefined.

This is because they're designed to work with the int values returned
by getc or fgetc; they need extra work to handle a char value.

If EOF is -1 (as it almost always is), with 8-bit bytes, the allowed
inputs to the ctype(3) functions are:

	{-1, 0, 1, 2, 3, ..., 255}.

However, on platforms where char is signed, such as x86 with the
usual ABI, code like

	char *arg = ...;
	... isspace(*arg) ...

may pass in values in the range:

	{-128, -127, -126, ..., -2, -1, 0, 1, ..., 127}.

This has two problems:

1. Inputs in the set {-128, -127, -126, ..., -2} are forbidden.

2. The non-EOF byte 0xff is conflated with the value EOF = -1, so
   even though the input is not forbidden, it may give the wrong
   answer.

Casting char to int first before passing the result to ctype(3)
doesn't help: inputs like -128 are unchanged by this cast.  It is
necessary to cast char inputs to unsigned char first; you can then
cast to int if you like but there's no need because the functions
will always convert the argument to int by definition.  So the above
fragment needs to be:

	char *arg = ...;
	... isspace((unsigned char)*arg) ...

This patch inserts unsigned char casts where necessary, and changes
int casts to unsigned char casts where the input is char.

I left alone int casts where the input is unsigned char already --
they're not immediately harmful, although they would have the effect
of suppressing some compiler warnings if the input is ever changed to
be char instead of unsigned char, so it might be better to remove
those casts too.

I also left alone calls where the input is int to begin with because
it came from getc; casting to unsigned char here would be wrong, of
course.

Signed-off-by: DL6ER <dl6er@dl6er.de>

src/dnsmasq/dhcp-common.c

@@ -838,7 +838,7 @@ char *option_string(int prot, unsigned int opt, unsigned char *val, int opt_len,
 		for (i = 0, j = 0; i < opt_len && j < buf_len ; i++)
 		  {
 		    char c = val[i];
-		    if (isprint((int)c))
+		    if (isprint((unsigned char)c))
 		      buf[j++] = c;
 		  }
 #ifdef HAVE_DHCP6
@@ -852,7 +852,7 @@ char *option_string(int prot, unsigned int opt, unsigned char *val, int opt_len,
 		    for (k = i + 1; k < opt_len && k < l && j < buf_len ; k++)
 		     {
 		       char c = val[k];
-		       if (isprint((int)c))
+		       if (isprint((unsigned char)c))
 			 buf[j++] = c;
 		     }
 		    i = l;
@@ -873,7 +873,7 @@ char *option_string(int prot, unsigned int opt, unsigned char *val, int opt_len,
 		    for (k = 0; k < len && j < buf_len; k++)
 		      {
 		       char c = *p++;
-		       if (isprint((int)c))
+		       if (isprint((unsigned char)c))
 			 buf[j++] = c;
 		     }
 		    i += len +2;

src/dnsmasq/dhcp.c

@@ -916,14 +916,14 @@ void dhcp_read_ethers(void)
       
       lineno++;
       
-      while (strlen(buff) > 0 && isspace((int)buff[strlen(buff)-1]))
+      while (strlen(buff) > 0 && isspace((unsigned char)buff[strlen(buff)-1]))
 	buff[strlen(buff)-1] = 0;
       
       if ((*buff == '#') || (*buff == '+') || (*buff == 0))
 	continue;
       
-      for (ip = buff; *ip && !isspace((int)*ip); ip++);
-      for(; *ip && isspace((int)*ip); ip++)
+      for (ip = buff; *ip && !isspace((unsigned char)*ip); ip++);
+      for(; *ip && isspace((unsigned char)*ip); ip++)
 	*ip = 0;
       if (!*ip || parse_hex(buff, hwaddr, ETHER_ADDR_LEN, NULL, NULL) != ETHER_ADDR_LEN)
 	{

src/dnsmasq/loop.c

@@ -92,7 +92,7 @@ int detect_loop(char *query, int type)
     return 0;
 
   for (i = 0; i < 8; i++)
-    if (!isxdigit(query[i]))
+    if (!isxdigit((unsigned char)query[i]))
       return 0;
 
   uid = strtol(query, NULL, 16);

src/dnsmasq/option.c

@@ -2755,7 +2755,7 @@ static int one_opt(int option, char *arg, char *errstr, char *gen_err, int comma
 		ret_err(gen_err);
 	      
 	      for (p = arg; *p; p++)
-		if (!isxdigit((int)*p))
+		if (!isxdigit((unsigned char)*p))
 		  ret_err(gen_err);
 	      
 	      set_option_bool(OPT_UMBRELLA_DEVID);
@@ -4840,7 +4840,7 @@ err:
 	    new->target = target;
 	    new->ttl = ttl;
 
-	    for (arg += arglen+1; *arg && isspace(*arg); arg++);
+	    for (arg += arglen+1; *arg && isspace((unsigned char)*arg); arg++);
 	  }
       
 	break;
@@ -5231,7 +5231,7 @@ err:
 	unhide_metas(keyhex);
 	/* 4034: "Whitespace is allowed within digits" */
 	for (cp = keyhex; *cp; )
-	  if (isspace(*cp))
+	  if (isspace((unsigned char)*cp))
 	    for (cp1 = cp; *cp1; cp1++)
 	      *cp1 = *(cp1+1);
 	  else
@@ -5319,7 +5319,7 @@ static void read_file(char *file, FILE *f, int hard_opt, int from_script)
 	      memmove(p, p+1, strlen(p+1)+1);
 	    }
 
-	  if (isspace(*p))
+	  if (isspace((unsigned char)*p))
 	    {
 	      *p = ' ';
 	      white = 1;

src/dnsmasq/rfc1035.c

@@ -520,7 +520,7 @@ static int print_txt(struct dns_header *header, const size_t qlen, char *name,
       /* make counted string zero-term and sanitise */
       for (i = 0; i < len; i++)
 	{
-	  if (!isprint((int)*(p3+1)))
+	  if (!isprint((unsigned char)*(p3+1)))
 	    break;
 	  *p3 = *(p3+1);
 	  p3++;

src/dnsmasq/rfc2131.c

@@ -1678,7 +1678,7 @@ static int sanitise(unsigned char *opt, char *buf)
   for (i = option_len(opt); i > 0; i--)
     {
       char c = *p++;
-      if (isprint((int)c))
+      if (isprint((unsigned char)c))
 	*buf++ = c;
     }
   *buf = 0; /* add terminator */

src/dnsmasq/tftp.c

@@ -405,7 +405,7 @@ void tftp_request(struct listener *listen, time_t now)
 	if (*p == '\\')
 	  *p = '/';
 	else if (option_bool(OPT_TFTP_LC))
-	  *p = tolower(*p);
+	  *p = tolower((unsigned char)*p);
 		
       strcpy(daemon->namebuff, "/");
       if (prefix)