linux-kernel - Re: KMSAN: uninit-value in alauda_check

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Date:   Wed, 29 Dec 2021 11:45:24 -0500
From:   Alan Stern <stern@...land.harvard.edu>
To:     Christophe JAILLET <christophe.jaillet@...adoo.fr>
Cc:     glider@...gle.com, gregkh@...uxfoundation.org,
        linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
        syzkaller-bugs@...glegroups.com,
        usb-storage@...ts.one-eyed-alien.net,
        Kernel Janitors <kernel-janitors@...r.kernel.org>
Subject: Re: KMSAN: uninit-value in alauda_check_media

On Wed, Dec 29, 2021 at 10:16:22AM +0100, Christophe JAILLET wrote:
> 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@google.com/
> > > 
> > > 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 :)

It is indeed old.  I doubt very many devices of this type are still in 
use.

> 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.

"if" and "memset" are both acceptable.  You can use either one.

Alan Stern