scsi: zfcp: Replace strlcpy() with strscpy()

strlcpy() reads the entire source buffer first. This read may exceed the
destination size limit. This is both inefficient and can lead to linear
read overflows if a source string is not NUL-terminated[1].  Additionally,
it returns the size of the source string, not the resulting size of the
destination string. In an effort to remove strlcpy() completely[2], replace
strlcpy() here with strscpy().

Overflow should be impossible here, but actually check for buffer sizes
being identical with BUILD_BUG_ON(), and include a run-time check as well.

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strlcpy [1]
Link: https://github.com/KSPP/linux/issues/89 [2]
Cc: Martin K. Petersen <martin.petersen@oracle.com>
Cc: James E.J. Bottomley <jejb@linux.ibm.com>
Cc: Steffen Maier <maier@linux.ibm.com>
Cc: Benjamin Block <bblock@linux.ibm.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Azeem Shaikh <azeemshaikh38@gmail.com>
Cc: <linux-s390@vger.kernel.org>
Cc: <linux-scsi@vger.kernel.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20231130204056.it.978-kees@kernel.orgAcked-by: Benjamin Block <bblock@linux.ibm.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/s390/scsi/zfcp_fc.c

@@ -900,8 +900,19 @@ static void zfcp_fc_rspn(struct zfcp_adapter *adapter,
 	zfcp_fc_ct_ns_init(&rspn_req->ct_hdr, FC_NS_RSPN_ID,
 			   FC_SYMBOLIC_NAME_SIZE);
 	hton24(rspn_req->rspn.fr_fid.fp_fid, fc_host_port_id(shost));
-	len = strlcpy(rspn_req->rspn.fr_name, fc_host_symbolic_name(shost),
-		      FC_SYMBOLIC_NAME_SIZE);
+
+	BUILD_BUG_ON(sizeof(rspn_req->name) !=
+			sizeof(fc_host_symbolic_name(shost)));
+	BUILD_BUG_ON(sizeof(rspn_req->name) !=
+			type_max(typeof(rspn_req->rspn.fr_name_len)) + 1);
+	len = strscpy(rspn_req->name, fc_host_symbolic_name(shost),
+		      sizeof(rspn_req->name));
+	/*
+	 * It should be impossible for this to truncate (see BUILD_BUG_ON()
+	 * above), but be robust anyway.
+	 */
+	if (WARN_ON(len < 0))
+		len = sizeof(rspn_req->name) - 1;
 	rspn_req->rspn.fr_name_len = len;
 
 	sg_init_one(&fc_req->sg_req, rspn_req, sizeof(*rspn_req));