scsi: libsas: Introduce struct smp_disc_resp

When compiling with gcc 12, several warnings are thrown by gcc when
compiling drivers/scsi/libsas/sas_expander.c, e.g.:

In function ‘sas_get_phy_change_count’,
inlined from ‘sas_find_bcast_phy.constprop’ at
drivers/scsi/libsas/sas_expander.c:1737:9:
drivers/scsi/libsas/sas_expander.c:1697:39: warning: array subscript
‘struct smp_resp[0]’ is partly outside array bounds of ‘unsigned
char[56]’ [-Warray-bounds]
1697 | *pcc = disc_resp->disc.change_count;
| ~~~~~~~~~~~~~~~^~~~~~~~~~~~~

This is due to the use of the struct smp_resp to aggregate all possible
response types using a union but allocating a response buffer with a size
exactly equal to the size of the response type needed. This leads to access
to fields of struct smp_resp from an allocated memory area that is smaller
than the size of struct smp_resp.

Fix this by defining struct smp_disc_resp for sas discovery operations.
Since this structure and the generic struct smp_resp are identical for
the little endian and big endian archs, move the definition of these
structures at the end of include/scsi/sas.h to avoid repeating their
definition.

Link: https://lore.kernel.org/r/[e-mail]
Reviewed-by: John Garry <[e-mail]>
Signed-off-by: Damien Le Moal <[e-mail]>
Signed-off-by: Martin K. Petersen <[e-mail]>

drivers/scsi/libsas/sas_expander.c

···
 		return dr->attached_dev_type;
 }
 
-static void sas_set_ex_phy(struct domain_device *dev, int phy_id, void *rsp)
+static void sas_set_ex_phy(struct domain_device *dev, int phy_id,
+			   struct smp_disc_resp *disc_resp)
 {
 	enum sas_device_type dev_type;
 	enum sas_linkrate linkrate;
 	u8 sas_addr[SAS_ADDR_SIZE];
-	struct smp_resp *resp = rsp;
-	struct discover_resp *dr = &resp->disc;
+	struct discover_resp *dr = &disc_resp->disc;
 	struct sas_ha_struct *ha = dev->port->ha;
 	struct expander_device *ex = &dev->ex_dev;
 	struct ex_phy *phy = &ex->ex_phy[phy_id];
···
 		BUG_ON(!phy->phy);
 	}
 
-	switch (resp->result) {
+	switch (disc_resp->result) {
 	case SMP_RESP_PHY_VACANT:
 		phy->phy_state = PHY_VACANT;
 		break;
···
 }
 
 #define DISCOVER_REQ_SIZE  16
-#define DISCOVER_RESP_SIZE 56
+#define DISCOVER_RESP_SIZE sizeof(struct smp_disc_resp)
 
 static int sas_ex_phy_discover_helper(struct domain_device *dev, u8 *disc_req,
-				      u8 *disc_resp, int single)
+				      struct smp_disc_resp *disc_resp,
+				      int single)
 {
-	struct discover_resp *dr;
+	struct discover_resp *dr = &disc_resp->disc;
 	int res;
 
 	disc_req[9] = single;
···
 			       disc_resp, DISCOVER_RESP_SIZE);
 	if (res)
 		return res;
-	dr = &((struct smp_resp *)disc_resp)->disc;
 	if (memcmp(dev->sas_addr, dr->attached_sas_addr, SAS_ADDR_SIZE) == 0) {
 		pr_notice("Found loopback topology, just ignore it!\n");
 		return 0;
···
 	struct expander_device *ex = &dev->ex_dev;
 	int  res = 0;
 	u8   *disc_req;
-	u8   *disc_resp;
+	struct smp_disc_resp *disc_resp;
 
 	disc_req = alloc_smp_req(DISCOVER_REQ_SIZE);
 	if (!disc_req)
···
 /* ---------- Domain revalidation ---------- */
 
 static int sas_get_phy_discover(struct domain_device *dev,
-				int phy_id, struct smp_resp *disc_resp)
+				int phy_id, struct smp_disc_resp *disc_resp)
 {
 	int res;
 	u8 *disc_req;
···
 			       disc_resp, DISCOVER_RESP_SIZE);
 	if (res)
 		goto out;
-	else if (disc_resp->result != SMP_RESP_FUNC_ACC) {
+	if (disc_resp->result != SMP_RESP_FUNC_ACC)
 		res = disc_resp->result;
-		goto out;
-	}
 out:
 	kfree(disc_req);
 	return res;
···
 				    int phy_id, int *pcc)
 {
 	int res;
-	struct smp_resp *disc_resp;
+	struct smp_disc_resp *disc_resp;
 
 	disc_resp = alloc_smp_resp(DISCOVER_RESP_SIZE);
 	if (!disc_resp)
···
 				    u8 *sas_addr, enum sas_device_type *type)
 {
 	int res;
-	struct smp_resp *disc_resp;
-	struct discover_resp *dr;
+	struct smp_disc_resp *disc_resp;
 
 	disc_resp = alloc_smp_resp(DISCOVER_RESP_SIZE);
 	if (!disc_resp)
 		return -ENOMEM;
-	dr = &disc_resp->disc;
 
 	res = sas_get_phy_discover(dev, phy_id, disc_resp);
 	if (res == 0) {
 		memcpy(sas_addr, disc_resp->disc.attached_sas_addr,
 		       SAS_ADDR_SIZE);
-		*type = to_dev_type(dr);
+		*type = to_dev_type(&disc_resp->disc);
 		if (*type == 0)
 			memset(sas_addr, 0, SAS_ADDR_SIZE);
 	}

include/scsi/sas.h

···
 	__be32 crc;
 } __attribute__ ((packed));
 
-struct smp_resp {
-	u8    frame_type;
-	u8    function;
-	u8    result;
-	u8    reserved;
-	union {
-		struct report_general_resp  rg;
-		struct discover_resp        disc;
-		struct report_phy_sata_resp rps;
-	};
-} __attribute__ ((packed));
-
 #elif defined(__BIG_ENDIAN_BITFIELD)
 struct sas_identify_frame {
 	/* Byte 0 */
···
 	__be32 crc;
 } __attribute__ ((packed));
 
+#else
+#error "Bitfield order not defined!"
+#endif
+
+struct smp_disc_resp {
+	u8    frame_type;
+	u8    function;
+	u8    result;
+	u8    reserved;
+	struct discover_resp disc;
+} __attribute__ ((packed));
+
 struct smp_resp {
 	u8    frame_type;
 	u8    function;
···
 		struct report_phy_sata_resp rps;
 	};
 } __attribute__ ((packed));
-
-#else
-#error "Bitfield order not defined!"
-#endif
 
 #endif /* _SAS_H_ */