ksmbd: fix -Wstringop-truncation warnings

Kernel test bot reports the following warnings:

   In function 'ndr_write_string',
       inlined from 'ndr_encode_dos_attr' at fs/ksmbd/ndr.c:136:3:
>> fs/ksmbd/ndr.c:70:2: warning: 'strncpy' destination unchanged after
copying no bytes [-Wstringop-truncation]
      70 |  strncpy(PAYLOAD_HEAD(n), value, sz);
         |  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   In function 'ndr_write_string',
       inlined from 'ndr_encode_dos_attr' at fs/ksmbd/ndr.c:134:3:
>> fs/ksmbd/ndr.c:70:2: warning: 'strncpy' output truncated before
terminating nul copying as many bytes from a string as its length
[-Wstringop-truncation]
      70 |  strncpy(PAYLOAD_HEAD(n), value, sz);
         |  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   fs/ksmbd/ndr.c: In function 'ndr_encode_dos_attr':
   fs/ksmbd/ndr.c:134:3: note: length computed here
     134 |   ndr_write_string(n, hex_attr, strlen(hex_attr));
         |   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Hyunchul Lee <hyc.lee@gmail.com>
Signed-off-by: Namjae Jeon <namjae.jeon@samsung.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/ksmbd/ndr.c

@@ -65,13 +65,15 @@ static int ndr_write_bytes(struct ndr *n, void *value, size_t sz)
 	return 0;
 }
 
-static int ndr_write_string(struct ndr *n, void *value, size_t sz)
+static int ndr_write_string(struct ndr *n, char *value)
 {
+	size_t sz;
+
+	sz = strlen(value) + 1;
 	if (n->length <= n->offset + sz)
 		try_to_realloc_ndr_blob(n, sz);
 
-	strncpy(ndr_get_field(n), value, sz);
-	sz++;
+	memcpy(ndr_get_field(n), value, sz);
 	n->offset += sz;
 	n->offset = ALIGN(n->offset, 2);
 	return 0;
@@ -134,9 +136,9 @@ int ndr_encode_dos_attr(struct ndr *n, struct xattr_dos_attrib *da)
 
 	if (da->version == 3) {
 		snprintf(hex_attr, 10, "0x%x", da->attr);
-		ndr_write_string(n, hex_attr, strlen(hex_attr));
+		ndr_write_string(n, hex_attr);
 	} else {
-		ndr_write_string(n, "", strlen(""));
+		ndr_write_string(n, "");
 	}
 	ndr_write_int16(n, da->version);
 	ndr_write_int32(n, da->version);