usb-storage: alauda: Fix uninit-value in alauda_check_media()

Syzbot got KMSAN to complain about access to an uninitialized value in
the alauda subdriver of usb-storage:

BUG: KMSAN: uninit-value in alauda_transport+0x462/0x57f0
drivers/usb/storage/alauda.c:1137
CPU: 0 PID: 12279 Comm: usb-storage Not tainted 5.3.0-rc7+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x191/0x1f0 lib/dump_stack.c:113
kmsan_report+0x13a/0x2b0 mm/kmsan/kmsan_report.c:108
__msan_warning+0x73/0xe0 mm/kmsan/kmsan_instr.c:250
alauda_check_media+0x344/0x3310 drivers/usb/storage/alauda.c:460

The problem is that alauda_check_media() doesn't verify that its USB
transfer succeeded before trying to use the received data. What
should happen if the transfer fails isn't entirely clear, but a
reasonably conservative approach is to pretend that no media is
present.

A similar problem exists in a usb_stor_dbg() call in
alauda_get_media_status(). In this case, when an error occurs the
call is redundant, because usb_stor_ctrl_transfer() already will print
a debugging message.

Finally, unrelated to the uninitialized memory access, is the fact
that alauda_check_media() performs DMA to a buffer on the stack.
Fortunately usb-storage provides a general purpose DMA-able buffer for
uses like this. We'll use it instead.

Reported-and-tested-by: [e-mail]
Closes: https://lore.kernel.org/all/[e-mail]/T/
Suggested-by: Christophe JAILLET <[e-mail]>
Signed-off-by: Alan Stern <[e-mail]>
Fixes: e80b0fade09e ("[PATCH] USB Storage: add alauda support")
Cc: <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/usb/storage/alauda.c

···
 	rc = usb_stor_ctrl_transfer(us, us->recv_ctrl_pipe,
 		command, 0xc0, 0, 1, data, 2);
 
-	usb_stor_dbg(us, "Media status %02X %02X\n", data[0], data[1]);
+	if (rc == USB_STOR_XFER_GOOD)
+		usb_stor_dbg(us, "Media status %02X %02X\n", data[0], data[1]);
 
 	return rc;
 }
···
 static int alauda_check_media(struct us_data *us)
 {
 	struct alauda_info *info = (struct alauda_info *) us->extra;
-	unsigned char status[2];
+	unsigned char *status = us->iobuf;
+	int rc;
 
-	alauda_get_media_status(us, status);
+	rc = alauda_get_media_status(us, status);
+	if (rc != USB_STOR_XFER_GOOD) {
+		status[0] = 0xF0;	/* Pretend there's no media */
+		status[1] = 0;
+	}
 
 	/* Check for no media or door open */
 	if ((status[0] & 0x80) || ((status[0] & 0x1F) == 0x10)