usb/msd: add usb_msd_fatal_error() and fix guest-triggerable assert

Add handler for fatal errors.  Moves device into error state where it
stops responding until the guest resets it.

Guest can send illegal requests where scsi command and usb packet
transfer directions are inconsistent.  Use the new usb_msd_fatal_error()
function instead of assert() in that case.

Reported-by: Qiang Liu <cyruscyliu@gmail.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Tested-by: Qiang Liu <cyruscyliu@gmail.com>
Message-Id: <20220830063827.813053-3-kraxel@redhat.com>

hw/usb/dev-storage.c

@@ -191,6 +191,23 @@ static void usb_msd_packet_complete(MSDState *s)
     usb_packet_complete(&s->dev, p);
 }
 
+static void usb_msd_fatal_error(MSDState *s)
+{
+    trace_usb_msd_fatal_error();
+
+    if (s->packet) {
+        s->packet->status = USB_RET_STALL;
+        usb_msd_packet_complete(s);
+    }
+
+    /*
+     * Guest messed up up device state with illegal requests.  Go
+     * ignore any requests until the guests resets the device (and
+     * brings it into a known state that way).
+     */
+    s->needs_reset = true;
+}
+
 static void usb_msd_copy_data(MSDState *s, USBPacket *p)
 {
     uint32_t len;
@@ -227,7 +244,11 @@ void usb_msd_transfer_data(SCSIRequest *req, uint32_t len)
     MSDState *s = DO_UPCAST(MSDState, dev.qdev, req->bus->qbus.parent);
     USBPacket *p = s->packet;
 
-    assert((s->mode == USB_MSDM_DATAOUT) == (req->cmd.mode == SCSI_XFER_TO_DEV));
+    if ((s->mode == USB_MSDM_DATAOUT) != (req->cmd.mode == SCSI_XFER_TO_DEV)) {
+        usb_msd_fatal_error(s);
+        return;
+    }
+
     s->scsi_len = len;
     s->scsi_off = 0;
     if (p) {
@@ -317,6 +338,8 @@ void usb_msd_handle_reset(USBDevice *dev)
 
     memset(&s->csw, 0, sizeof(s->csw));
     s->mode = USB_MSDM_CBW;
+
+    s->needs_reset = false;
 }
 
 static void usb_msd_handle_control(USBDevice *dev, USBPacket *p,
@@ -382,6 +405,11 @@ static void usb_msd_handle_data(USBDevice *dev, USBPacket *p)
     SCSIDevice *scsi_dev;
     uint32_t len;
 
+    if (s->needs_reset) {
+        p->status = USB_RET_STALL;
+        return;
+    }
+
     switch (p->pid) {
     case USB_TOKEN_OUT:
         if (devep != 2)

hw/usb/trace-events

@@ -263,6 +263,7 @@ usb_msd_packet_complete(void) ""
 usb_msd_cmd_submit(unsigned lun, unsigned tag, unsigned flags, unsigned len, unsigned data_len) "lun %u, tag 0x%x, flags 0x%08x, len %d, data-len %d"
 usb_msd_cmd_complete(unsigned status, unsigned tag) "status %d, tag 0x%x"
 usb_msd_cmd_cancel(unsigned tag) "tag 0x%x"
+usb_msd_fatal_error(void) ""
 
 # dev-uas.c
 usb_uas_reset(int addr) "dev %d"

include/hw/usb/msd.h

@@ -40,6 +40,7 @@ struct MSDState {
     bool removable;
     bool commandlog;
     SCSIDevice *scsi_dev;
+    bool needs_reset;
 };
 
 typedef struct MSDState MSDState;