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: https://github.com/KSPP/linux/issues/90
Cc: [e-mail]
Signed-off-by: Justin Stitt <[e-mail]>
Link: https://lore.kernel.org/r/2[e-mail]
Reviewed-by: Kees Cook <[e-mail]>
Signed-off-by: Martin K. Petersen <[e-mail]>

drivers/scsi/libfc/fc_encode.h

···
 		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;