[SCSI] libfc: fix lun reset failure bugs in fc_fcp_resp handling of FCP_RSP_INFO

In LUN RESET testing involving NetApp targets, it is observed that LUN
RESET is failing. The fc_fcp_resp() is not completing the completion
for the LUN RESET task since fc_fcp_resp assumes that the FCP_RSP_INFO
is 8 bytes with the 4 byte reserved field, where in case of NetApp targets
the FCP_RSP to LUN RESET only has 4 bytes of FCP_RSP_INFO. This leads
fc_fcp_resp to error out w/o completing the task completion, eventually
causing LUN RESET to be escalated to host reset, which is not very nice.

Per FCP-3 r04, clause 9.5.15 and Table 23, the FCP_RSP_INFO field can be either
4 bytes or 8 bytes, with the last 4 bytes as "Reserved (if any)". Therefore it
is valid to have 4 bytes FCP_RSP_INFO like some of the NetApp targets behave.
Fixing this by validating the FCP_RSP_INFO against both the two spec allowed
length.

Reported-by: Frank Zhang <[e-mail]>
Signed-off-by: Yi Zou <[e-mail]>
Tested-by: Ross Brattain <[e-mail]>
Signed-off-by: Robert Love <[e-mail]>
Signed-off-by: James Bottomley <[e-mail]>

drivers/scsi/libfc/fc_fcp.c

···
 			fc_rp_info = (struct fcp_resp_rsp_info *)(rp_ex + 1);
 			if (flags & FCP_RSP_LEN_VAL) {
 				respl = ntohl(rp_ex->fr_rsp_len);
-				if (respl != sizeof(*fc_rp_info))
+				if ((respl != FCP_RESP_RSP_INFO_LEN4) &&
+				    (respl != FCP_RESP_RSP_INFO_LEN8))
 					goto len_err;
 				if (fsp->wait_for_comp) {
 					/* Abuse cdb_status for rsp code */

include/scsi/fc/fc_fcp.h

···
  *
  * All response frames will always contain the fcp_resp template.  Some
  * will also include the fcp_resp_len template.
+ *
+ * From Table 23, the FCP_RSP_INFO can either be 4 bytes or 8 bytes, both
+ * are valid length.
  */
 struct fcp_resp {
 	__u8		_fr_resvd[8];	/* reserved */
···
     __u8      rsp_code;           /* Response Info Code */
     __u8      _fr_resvd2[4];      /* reserved */
 };
+
+#define FCP_RESP_RSP_INFO_LEN4    4 /* without reserved field */
+#define FCP_RESP_RSP_INFO_LEN8    8 /* with reserved field */
 
 struct fcp_resp_with_ext {
 	struct fcp_resp resp;