megasas: do not read DCMD opcode more than once from frame

Avoid TOC-TOU bugs by storing the DCMD opcode in the MegasasCmd
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

hw/scsi/megasas.c

@@ -63,6 +63,7 @@ typedef struct MegasasCmd {
 
     hwaddr pa;
     hwaddr pa_size;
+    uint32_t dcmd_opcode;
     union mfi_frame *frame;
     SCSIRequest *req;
     QEMUSGList qsg;
@@ -513,6 +514,7 @@ static MegasasCmd *megasas_enqueue_frame(MegasasState *s,
         cmd->context &= (uint64_t)0xFFFFFFFF;
     }
     cmd->count = count;
+    cmd->dcmd_opcode = -1;
     s->busy++;
 
     if (s->consumer_pa) {
@@ -1562,22 +1564,21 @@ static const struct dcmd_cmd_tbl_t {
 
 static int megasas_handle_dcmd(MegasasState *s, MegasasCmd *cmd)
 {
-    int opcode;
     int retval = 0;
     size_t len;
     const struct dcmd_cmd_tbl_t *cmdptr = dcmd_cmd_tbl;
 
-    opcode = le32_to_cpu(cmd->frame->dcmd.opcode);
-    trace_megasas_handle_dcmd(cmd->index, opcode);
+    cmd->dcmd_opcode = le32_to_cpu(cmd->frame->dcmd.opcode);
+    trace_megasas_handle_dcmd(cmd->index, cmd->dcmd_opcode);
     if (megasas_map_dcmd(s, cmd) < 0) {
         return MFI_STAT_MEMORY_NOT_AVAILABLE;
     }
-    while (cmdptr->opcode != -1 && cmdptr->opcode != opcode) {
+    while (cmdptr->opcode != -1 && cmdptr->opcode != cmd->dcmd_opcode) {
         cmdptr++;
     }
     len = cmd->iov_size;
     if (cmdptr->opcode == -1) {
-        trace_megasas_dcmd_unhandled(cmd->index, opcode, len);
+        trace_megasas_dcmd_unhandled(cmd->index, cmd->dcmd_opcode, len);
         retval = megasas_dcmd_dummy(s, cmd);
     } else {
         trace_megasas_dcmd_enter(cmd->index, cmdptr->desc, len);
@@ -1592,13 +1593,11 @@ static int megasas_handle_dcmd(MegasasState *s, MegasasCmd *cmd)
 static int megasas_finish_internal_dcmd(MegasasCmd *cmd,
                                         SCSIRequest *req)
 {
-    int opcode;
     int retval = MFI_STAT_OK;
     int lun = req->lun;
 
-    opcode = le32_to_cpu(cmd->frame->dcmd.opcode);
-    trace_megasas_dcmd_internal_finish(cmd->index, opcode, lun);
-    switch (opcode) {
+    trace_megasas_dcmd_internal_finish(cmd->index, cmd->dcmd_opcode, lun);
+    switch (cmd->dcmd_opcode) {
     case MFI_DCMD_PD_GET_INFO:
         retval = megasas_pd_get_info_submit(req->dev, lun, cmd);
         break;
@@ -1606,7 +1605,7 @@ static int megasas_finish_internal_dcmd(MegasasCmd *cmd,
         retval = megasas_ld_get_info_submit(req->dev, lun, cmd);
         break;
     default:
-        trace_megasas_dcmd_internal_invalid(cmd->index, opcode);
+        trace_megasas_dcmd_internal_invalid(cmd->index, cmd->dcmd_opcode);
         retval = MFI_STAT_INVALID_DCMD;
         break;
     }
@@ -1827,7 +1826,6 @@ static void megasas_xfer_complete(SCSIRequest *req, uint32_t len)
 {
     MegasasCmd *cmd = req->hba_private;
     uint8_t *buf;
-    uint32_t opcode;
 
     trace_megasas_io_complete(cmd->index, len);
 
@@ -1837,8 +1835,7 @@ static void megasas_xfer_complete(SCSIRequest *req, uint32_t len)
     }
 
     buf = scsi_req_get_buf(req);
-    opcode = le32_to_cpu(cmd->frame->dcmd.opcode);
-    if (opcode == MFI_DCMD_PD_GET_INFO && cmd->iov_buf) {
+    if (cmd->dcmd_opcode == MFI_DCMD_PD_GET_INFO && cmd->iov_buf) {
         struct mfi_pd_info *info = cmd->iov_buf;
 
         if (info->inquiry_data[0] == 0x7f) {
@@ -1849,7 +1846,7 @@ static void megasas_xfer_complete(SCSIRequest *req, uint32_t len)
             memcpy(info->vpd_page83, buf, len);
         }
         scsi_req_continue(req);
-    } else if (opcode == MFI_DCMD_LD_GET_INFO) {
+    } else if (cmd->dcmd_opcode == MFI_DCMD_LD_GET_INFO) {
         struct mfi_ld_info *info = cmd->iov_buf;
 
         if (cmd->iov_buf) {