scsi: libsas: Introduce struct smp_rg_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_ex_change_count’,
inlined from ‘sas_find_bcast_dev’ at
drivers/scsi/libsas/sas_expander.c:1816:8:
drivers/scsi/libsas/sas_expander.c:1781:20: warning: array subscript
‘struct smp_resp[0]’ is partly outside array bounds of ‘unsigned
char[32]’ [-Warray-bounds]
1781 | if (rg_resp->result != SMP_RESP_FUNC_ACC) {
| ~~~~~~~^~~~~~~~

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_rg_resp for sas report general responses.

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

···
 
 #define MAX_EXPANDER_PHYS 128
 
-static void ex_assign_report_general(struct domain_device *dev,
-					    struct smp_resp *resp)
-{
-	struct report_general_resp *rg = &resp->rg;
-
-	dev->ex_dev.ex_change_count = be16_to_cpu(rg->change_count);
-	dev->ex_dev.max_route_indexes = be16_to_cpu(rg->route_indexes);
-	dev->ex_dev.num_phys = min(rg->num_phys, (u8)MAX_EXPANDER_PHYS);
-	dev->ex_dev.t2t_supp = rg->t2t_supp;
-	dev->ex_dev.conf_route_table = rg->conf_route_table;
-	dev->ex_dev.configuring = rg->configuring;
-	memcpy(dev->ex_dev.enclosure_logical_id, rg->enclosure_logical_id, 8);
-}
-
 #define RG_REQ_SIZE   8
-#define RG_RESP_SIZE 32
+#define RG_RESP_SIZE  sizeof(struct smp_rg_resp)
 
 static int sas_ex_general(struct domain_device *dev)
 {
 	u8 *rg_req;
-	struct smp_resp *rg_resp;
+	struct smp_rg_resp *rg_resp;
+	struct report_general_resp *rg;
 	int res;
 	int i;
 
···
 			goto out;
 		}
 
-		ex_assign_report_general(dev, rg_resp);
+		rg = &rg_resp->rg;
+		dev->ex_dev.ex_change_count = be16_to_cpu(rg->change_count);
+		dev->ex_dev.max_route_indexes = be16_to_cpu(rg->route_indexes);
+		dev->ex_dev.num_phys = min(rg->num_phys, (u8)MAX_EXPANDER_PHYS);
+		dev->ex_dev.t2t_supp = rg->t2t_supp;
+		dev->ex_dev.conf_route_table = rg->conf_route_table;
+		dev->ex_dev.configuring = rg->configuring;
+		memcpy(dev->ex_dev.enclosure_logical_id,
+		       rg->enclosure_logical_id, 8);
 
 		if (dev->ex_dev.configuring) {
 			pr_debug("RG: ex %016llx self-configuring...\n",
···
 {
 	int res;
 	u8  *rg_req;
-	struct smp_resp  *rg_resp;
+	struct smp_rg_resp  *rg_resp;
 
 	rg_req = alloc_smp_req(RG_REQ_SIZE);
 	if (!rg_req)

include/scsi/sas.h

···
 #error "Bitfield order not defined!"
 #endif
 
+struct smp_rg_resp {
+	u8    frame_type;
+	u8    function;
+	u8    result;
+	u8    reserved;
+	struct report_general_resp rg;
+} __attribute__ ((packed));
+
 struct smp_disc_resp {
 	u8    frame_type;
 	u8    function;