Re: KMSAN: uninit-value in alauda_check_media

[Christophe JAILLET]

Le 28/12/2021 à 23:49, Alan Stern a écrit :
> On Tue, Dec 28, 2021 at 08:47:15AM +0100, Christophe JAILLET wrote:
> > Hi,
> >
> > (2nd try - text only format - sorry for the noise)
> >
> >
> > first try to use syzbot. I hope I do it right.
> > Discussion about the syz report can be found at
> > https://lore.kernel.org/linux-kernel/0000000000007d25ff059457342d@xxxxxxxxxx/
> >
> > This patch only test if alauda_get_media_status() (and its embedded
> > usb_stor_ctrl_transfer()) before using the data.
> > In case of error, it returns USB_STOR_TRANSPORT_ERROR as done elsewhere.
> >
> > #syz test: git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git
> > master
> >
> > CJ
>
> > diff --git a/drivers/usb/storage/alauda.c b/drivers/usb/storage/alauda.c
> > index 20b857e97e60..6c486d964911 100644
> > --- a/drivers/usb/storage/alauda.c
> > +++ b/drivers/usb/storage/alauda.c
> > @@ -318,7 +318,8 @@ static int alauda_get_media_status(struct us_data *us, unsigned char *data)
> >   	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]);
>
> Instead of adding this test, you could initialize data[0] and data[1]
> to zero before the call to usb_stor_ctrl_transfer.

Well, having the test is cleaner, IMHO.
If usb_stor_ctrl_transfer() fails, a message explaining the reason is 
already generated by the same usb_stor_dbg(). Having an error message 
followed by another one stating that the Media Status is 0x00 0x00 could 
be confusing I think.

Let me know if you have a real preference for a memset(data, 0, 2).
If so, I'll add it.

> >   
> >   	return rc;
> >   }
> > @@ -453,8 +454,11 @@ static int alauda_check_media(struct us_data *us)
> >   {
> >   	struct alauda_info *info = (struct alauda_info *) us->extra;
> >   	unsigned char status[2];
> > +	int rc;
> >   
> > -	alauda_get_media_status(us, status);
> > +	rc = alauda_get_media_status(us, status);
> > +	if (rc != USB_STOR_TRANSPORT_GOOD)
> > +		return USB_STOR_TRANSPORT_ERROR;
> >   
> >   	/* Check for no media or door open */
> >   	if ((status[0] & 0x80) || ((status[0] & 0x1F) == 0x10)
>
> In general this looks fine.  Let us know when you are ready to submit
> the patch.

I was unsure that this patch would get any interest because the driver 
looks old. That's why I first tried to play with syzbot :)

In the syzbot history, you also mentioned that 'unsigned char status[2]' 
should be 'unsigned char *status = us->iobuf;'

This is more a blind fix for me, but it looks consistent with other 
places that call alauda_get_media_status().

So, once you confirm if you prefer my 'if' or a 'memset', I'll resend a 
small serie for fixing both issues.

CJ


> Alan Stern