lib: add error checking to hex2bin

hex2bin converts a hexadecimal string to its binary representation.
The original version of hex2bin did not do any error checking.  This
patch adds error checking and returns the result.

Changelog v1:
- removed unpack_hex_byte()
- changed return code from boolean to int

Changelog:
- use the new unpack_hex_byte()
- add __must_check compiler option (Andy Shevchenko's suggestion)
- change function API to return error checking result
  (based on Tetsuo Handa's initial patch)
Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
Acked-by: Andy Shevchenko <andy.shevchenko@gmail.com>

include/linux/kernel.h

@@ -382,7 +382,7 @@ static inline char *pack_hex_byte(char *buf, u8 byte)
 }
 
 extern int hex_to_bin(char ch);
-extern void hex2bin(u8 *dst, const char *src, size_t count);
+extern int __must_check hex2bin(u8 *dst, const char *src, size_t count);
 
 /*
  * General tracing related utility functions - trace_printk(),

lib/hexdump.c

@@ -38,14 +38,21 @@ EXPORT_SYMBOL(hex_to_bin);
  * @dst: binary result
  * @src: ascii hexadecimal string
  * @count: result length
+ *
+ * Return 0 on success, -1 in case of bad input.
  */
-void hex2bin(u8 *dst, const char *src, size_t count)
+int hex2bin(u8 *dst, const char *src, size_t count)
 {
 	while (count--) {
-		*dst = hex_to_bin(*src++) << 4;
-		*dst += hex_to_bin(*src++);
-		dst++;
+		int hi = hex_to_bin(*src++);
+		int lo = hex_to_bin(*src++);
+
+		if ((hi < 0) || (lo < 0))
+			return -1;
+
+		*dst++ = (hi << 4) | lo;
 	}
+	return 0;
 }
 EXPORT_SYMBOL(hex2bin);