efi_loader: fix off-by-one bug in efi_get_variable

efi_get_variable() always stores an extra zero byte after the output data.
When the returned data size matches the output buffer size, the extra zero
byte is stored past the end of the output buffer.
Signed-off-by: NIvan Gorinov <ivan.gorinov@intel.com>
Reviewed-by: NHeinrich Schuchardt <xypron.glpk@gmx.de>
Signed-off-by: NAlexander Graf <agraf@suse.de>

lib/efi_loader/efi_variable.c

@@ -49,7 +49,7 @@
 	(strlen("efi_xxxxxxxx-xxxx-xxxx-xxxxxxxxxxxxxxxx_") + \
 		(MAX_VAR_NAME * MAX_UTF8_PER_UTF16))
 
-static int hex(unsigned char ch)
+static int hex(int ch)
 {
 	if (ch >= 'a' && ch <= 'f')
 		return ch-'a'+10;
@@ -60,44 +60,32 @@ static int hex(unsigned char ch)
 	return -1;
 }
 
-static const char *hex2mem(u8 *mem, const char *hexstr, int count)
+static int hex2mem(u8 *mem, const char *hexstr, int size)
 {
-	memset(mem, 0, count/2);
+	int nibble;
+	int i;
 
-	do {
-		int nibble;
-
-		*mem = 0;
-
-		if (!count || !*hexstr)
+	for (i = 0; i < size; i++) {
+		if (*hexstr == '\0')
 			break;
 
 		nibble = hex(*hexstr);
 		if (nibble < 0)
-			break;
+			return -1;
 
 		*mem = nibble;
-		count--;
 		hexstr++;
 
-		if (!count || !*hexstr)
-			break;
-
 		nibble = hex(*hexstr);
 		if (nibble < 0)
-			break;
+			return -1;
 
 		*mem = (*mem << 4) | nibble;
-		count--;
 		hexstr++;
 		mem++;
+	}
 
-	} while (1);
-
-	if (*hexstr)
-		return hexstr;
-
-	return NULL;
+	return i;
 }
 
 static char *mem2hex(char *hexstr, const u8 *mem, int count)
@@ -209,8 +197,12 @@ efi_status_t EFIAPI efi_get_variable(u16 *variable_name, efi_guid_t *vendor,
 	if ((s = prefix(val, "(blob)"))) {
 		unsigned len = strlen(s);
 
+		/* number of hexadecimal digits must be even */
+		if (len & 1)
+			return EFI_EXIT(EFI_DEVICE_ERROR);
+
 		/* two characters per byte: */
-		len = DIV_ROUND_UP(len, 2);
+		len /= 2;
 		*data_size = len;
 
 		if (in_size < len)
@@ -219,7 +211,7 @@ efi_status_t EFIAPI efi_get_variable(u16 *variable_name, efi_guid_t *vendor,
 		if (!data)
 			return EFI_EXIT(EFI_INVALID_PARAMETER);
 
-		if (hex2mem(data, s, len * 2))
+		if (hex2mem(data, s, len) != len)
 			return EFI_EXIT(EFI_DEVICE_ERROR);
 
 		debug("%s: got value: \"%s\"\n", __func__, s);