scsi: libfc: replace deprecated strncpy() with memcpy()

strncpy() is deprecated [1] and as such we should use different apis to
copy string data.

We can see that ct is NUL-initialized with fc_ct_hdr_fill:
|       ct = fc_ct_hdr_fill(fp, op, sizeof(struct fc_ns_rspn) + len,
...

In fc_ct_hdr_fill():
|       memset(ct, 0, ct_plen);

We also calculate the length of the source string:
|       len = strnlen(fc_host_symbolic_name(lport->host), 255);

...then this argument is used in strncpy(), which is bad because the
pattern of (dest, src, strlen(src)) usually leaves the destination
buffer without NUL-termination. However, it looks as though we do not
require NUL-termination since fr_name is part of a seq_buf-like
structure wherein its length is monitored:
|       struct fc_ns_rspn {
|       	struct fc_ns_fid fr_fid;	/* port ID object */
|       	__u8		fr_name_len;
|       	char		fr_name[];
|       } __attribute__((__packed__));

So, this is really just a byte copy into a length-bounded buffer. Let's use
memcpy().

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
Link: KSPP#90
Cc: linux-hardening@vger.kernel.org
Signed-off-by: Justin Stitt <justinstitt@google.com>
Link: https://lore.kernel.org/r/20240221-strncpy-drivers-scsi-libfc-fc_encode-h-v2-1-019a0889c5ca@google.com
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

Author: JustinStitt

drivers/scsi/libfc/fc_encode.h

@@ -136,22 +136,24 @@ static inline int fc_ct_ns_fill(struct fc_lport *lport,
 		break;
 
 	case FC_NS_RSPN_ID:
-		len = strnlen(fc_host_symbolic_name(lport->host), 255);
+		len = strnlen(fc_host_symbolic_name(lport->host),
+			      FC_SYMBOLIC_NAME_SIZE);
 		ct = fc_ct_hdr_fill(fp, op, sizeof(struct fc_ns_rspn) + len,
 				    FC_FST_DIR, FC_NS_SUBTYPE);
 		hton24(ct->payload.spn.fr_fid.fp_fid, lport->port_id);
-		strncpy(ct->payload.spn.fr_name,
-			fc_host_symbolic_name(lport->host), len);
+		memcpy(ct->payload.spn.fr_name,
+		       fc_host_symbolic_name(lport->host), len);
 		ct->payload.spn.fr_name_len = len;
 		break;
 
 	case FC_NS_RSNN_NN:
-		len = strnlen(fc_host_symbolic_name(lport->host), 255);
+		len = strnlen(fc_host_symbolic_name(lport->host),
+			      FC_SYMBOLIC_NAME_SIZE);
 		ct = fc_ct_hdr_fill(fp, op, sizeof(struct fc_ns_rsnn) + len,
 				    FC_FST_DIR, FC_NS_SUBTYPE);
 		put_unaligned_be64(lport->wwnn, &ct->payload.snn.fr_wwn);
-		strncpy(ct->payload.snn.fr_name,
-			fc_host_symbolic_name(lport->host), len);
+		memcpy(ct->payload.snn.fr_name,
+		       fc_host_symbolic_name(lport->host), len);
 		ct->payload.snn.fr_name_len = len;
 		break;