scsi: target: Handle short iSIDs

SPC4 has:

The first ISCSI INITIATOR SESSION ID field byte containing an ASCII null
character terminates the ISCSI INITIATOR SESSION ID field without regard
for the specified length of the iSCSI TransportID or the contents of the
ADDITIONAL LENGTH field.
----------------------------------------

which sounds like we can get an iSID shorter than 12 chars. SPC and the
iSCSI RFC do not say how to handle that case other than just cutting off
the iSID. This patch just makes sure that if we get an iSID like that, we
only copy/send that string.

There is no OS that does this right now, so there was no test case.  I did
test with sg utils to check it works as expected and nothing breaks.

Link: https://lore.kernel.org/r/1593654203-12442-8-git-send-email-michael.christie@oracle.comSigned-off-by: Mike Christie <michael.christie@oracle.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/target/target_core_fabric_lib.c

@@ -132,6 +132,7 @@ static int iscsi_get_pr_transport_id(
 	unsigned char *buf)
 {
 	u32 off = 4, padding = 0;
+	int isid_len;
 	u16 len = 0;
 
 	spin_lock_irq(&se_nacl->nacl_sess_lock);
@@ -184,11 +185,11 @@ static int iscsi_get_pr_transport_id(
 		buf[off++] = 0x2c; /* ASCII Character: "," */
 		buf[off++] = 0x30; /* ASCII Character: "0" */
 		buf[off++] = 0x78; /* ASCII Character: "x" */
+		len += 5;
 
-		memcpy(buf + off, pr_reg->pr_reg_isid, 12);
-		off += 12;
-
-		len += 17;
+		isid_len = sprintf(buf + off, "%s", pr_reg->pr_reg_isid);
+		off += isid_len;
+		len += isid_len;
 	}
 	buf[off] = '\0';
 	len += 1;
@@ -234,7 +235,7 @@ static int iscsi_get_pr_transport_id_len(
 	 */
 	if (pr_reg->isid_present_at_reg) {
 		len += 5; /* For ",i,0x" ASCII separator */
-		len += 12; /* For iSCSI Initiator Session ID */
+		len += strlen(pr_reg->pr_reg_isid);
 		*format_code = 1;
 	} else
 		*format_code = 0;
@@ -318,6 +319,16 @@ static char *iscsi_parse_pr_out_transport_id(
 		 * iscsi_target.c:lio_sess_get_initiator_sid()
 		 */
 		for (i = 0; i < 12; i++) {
+			/*
+			 * The first ISCSI INITIATOR SESSION ID field byte
+			 * containing an ASCII null character terminates the
+			 * ISCSI INITIATOR SESSION ID field without regard for
+			 * the specified length of the iSCSI TransportID or the
+			 * contents of the ADDITIONAL LENGTH field.
+			 */
+			if (*p == '\0')
+				break;
+
 			if (isdigit(*p)) {
 				p++;
 				continue;