scsi: qla2xxx: Fix memcpy() field-spanning write issue

purex_item.iocb is defined as a 64-element u8 array, but 64 is the
minimum size and it can be allocated larger. This makes it a standard
empty flex array.

This was motivated by field-spanning write warnings during FPIN testing:

https://lore.kernel.org/linux-nvme/20250709211919.49100-1-bgurney@redhat.com/

  >  kernel: memcpy: detected field-spanning write (size 60) of single field
  >  "((uint8_t *)fpin_pkt + buffer_copy_offset)"
  >  at drivers/scsi/qla2xxx/qla_isr.c:1221 (size 44)

I removed the outer wrapper from the iocb flex array, so that it can be
linked to 'purex_item.size' with '__counted_by'.

These changes remove the default minimum 64-byte allocation, requiring
further changes.

  In 'struct scsi_qla_host' the embedded 'default_item' is now followed
  by '__default_item_iocb[QLA_DEFAULT_PAYLOAD_SIZE]' to reserve space
  that will be used as 'default_item.iocb'. This is wrapped using the
  'TRAILING_OVERLAP()' macro helper, which effectively creates a union
  between flexible-array member 'default_item.iocb' and
  '__default_item_iocb'.

  Since 'struct pure_item' now contains a flexible-array member, the
  helper must be placed at the end of 'struct scsi_qla_host' to prevent
  a '-Wflex-array-member-not-at-end' warning.

  'qla24xx_alloc_purex_item()' is adjusted to no longer expect the
  default minimum size to be part of 'sizeof(struct purex_item)', the
  entire flexible array size is added to the structure size for
  allocation.

This also slightly changes the layout of the purex_item struct, as
2-bytes of padding are added between 'size' and 'iocb'. The resulting
size is the same, but iocb is shifted 2-bytes (the original 'purex_item'
structure was padded at the end, after the 64-byte defined array size).
I don't think this is a problem.

Tested-by: Bryan Gurney <bgurney@redhat.com>
Co-developed-by: Chris Leech <cleech@redhat.com>
Signed-off-by: Chris Leech <cleech@redhat.com>
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Link: https://lore.kernel.org/r/20250813200744.17975-10-bgurney@redhat.com
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

Author: GustavoARSilva

drivers/scsi/qla2xxx/qla_def.h

@@ -4890,9 +4890,7 @@ struct purex_item {
 			     struct purex_item *pkt);
 	atomic_t in_use;
 	uint16_t size;
-	struct {
-		uint8_t iocb[64];
-	} iocb;
+	uint8_t iocb[] __counted_by(size);
 };
 
 #include "qla_edif.h"
@@ -5101,7 +5099,6 @@ typedef struct scsi_qla_host {
 		struct list_head head;
 		spinlock_t lock;
 	} purex_list;
-	struct purex_item default_item;
 
 	struct name_list_extended gnl;
 	/* Count of active session/fcport */
@@ -5130,6 +5127,11 @@ typedef struct scsi_qla_host {
 #define DPORT_DIAG_IN_PROGRESS                 BIT_0
 #define DPORT_DIAG_CHIP_RESET_IN_PROGRESS      BIT_1
 	uint16_t dport_status;
+
+	/* Must be last --ends in a flexible-array member. */
+	TRAILING_OVERLAP(struct purex_item, default_item, iocb,
+		uint8_t __default_item_iocb[QLA_DEFAULT_PAYLOAD_SIZE];
+	);
 } scsi_qla_host_t;
 
 struct qla27xx_image_status {

drivers/scsi/qla2xxx/qla_isr.c

@@ -1077,17 +1077,17 @@ static struct purex_item *
 qla24xx_alloc_purex_item(scsi_qla_host_t *vha, uint16_t size)
 {
 	struct purex_item *item = NULL;
-	uint8_t item_hdr_size = sizeof(*item);
 
 	if (size > QLA_DEFAULT_PAYLOAD_SIZE) {
-		item = kzalloc(item_hdr_size +
-		    (size - QLA_DEFAULT_PAYLOAD_SIZE), GFP_ATOMIC);
+		item = kzalloc(struct_size(item, iocb, size), GFP_ATOMIC);
 	} else {
 		if (atomic_inc_return(&vha->default_item.in_use) == 1) {
 			item = &vha->default_item;
 			goto initialize_purex_header;
 		} else {
-			item = kzalloc(item_hdr_size, GFP_ATOMIC);
+			item = kzalloc(
+				struct_size(item, iocb, QLA_DEFAULT_PAYLOAD_SIZE),
+				GFP_ATOMIC);
 		}
 	}
 	if (!item) {
@@ -1127,17 +1127,16 @@ qla24xx_queue_purex_item(scsi_qla_host_t *vha, struct purex_item *pkt,
  * @vha: SCSI driver HA context
  * @pkt: ELS packet
  */
-static struct purex_item
-*qla24xx_copy_std_pkt(struct scsi_qla_host *vha, void *pkt)
+static struct purex_item *
+qla24xx_copy_std_pkt(struct scsi_qla_host *vha, void *pkt)
 {
 	struct purex_item *item;
 
-	item = qla24xx_alloc_purex_item(vha,
-					QLA_DEFAULT_PAYLOAD_SIZE);
+	item = qla24xx_alloc_purex_item(vha, QLA_DEFAULT_PAYLOAD_SIZE);
 	if (!item)
 		return item;
 
-	memcpy(&item->iocb, pkt, sizeof(item->iocb));
+	memcpy(&item->iocb, pkt, QLA_DEFAULT_PAYLOAD_SIZE);
 	return item;
 }
 

drivers/scsi/qla2xxx/qla_nvme.c

@@ -1308,7 +1308,7 @@ void qla2xxx_process_purls_iocb(void **pkt, struct rsp_que **rsp)
 
 	ql_dbg(ql_dbg_unsol, vha, 0x2121,
 	       "PURLS OP[%01x] size %d xchg addr 0x%x portid %06x\n",
-	       item->iocb.iocb[3], item->size, uctx->exchange_address,
+	       item->iocb[3], item->size, uctx->exchange_address,
 	       fcport->d_id.b24);
 	/* +48    0  1  2  3  4  5  6  7  8  9  A  B  C  D  E  F
 	 * ----- -----------------------------------------------

drivers/scsi/qla2xxx/qla_os.c

@@ -6459,9 +6459,10 @@ void qla24xx_process_purex_rdp(struct scsi_qla_host *vha,
 void
 qla24xx_free_purex_item(struct purex_item *item)
 {
-	if (item == &item->vha->default_item)
+	if (item == &item->vha->default_item) {
 		memset(&item->vha->default_item, 0, sizeof(struct purex_item));
-	else
+		memset(&item->vha->__default_item_iocb, 0, QLA_DEFAULT_PAYLOAD_SIZE);
+	} else
 		kfree(item);
 }