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Date:   Sat, 26 Oct 2019 12:40:10 +0900
From:   Suwan Kim <suwan.kim027@gmail.com>
To:     shuah <shuah@kernel.org>
Cc:     Dan Carpenter <dan.carpenter@oracle.com>, kbuild@lists.01.org,
        kbuild-all@lists.01.org, linux-kernel@vger.kernel.org,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-usb@vger.kernel.org
Subject: Re: drivers/usb/usbip/stub_rx.c:505 stub_recv_cmd_submit() error:
 uninitialized symbol 'nents'.
Message-ID: <20191026034010.GA6411@localhost.localdomain>
References: <20191022092839.GD10833@kadam>
 <20191023071120.GA3061@localhost.localdomain>
 <20191024194500.GD23523@kadam>
 <ce76c90b-3431-9342-8b75-882d582c6366@kernel.org>
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On Thu, Oct 24, 2019 at 04:52:52PM -0600, shuah wrote:
> On 10/24/19 1:45 PM, Dan Carpenter wrote:
> > On Wed, Oct 23, 2019 at 04:11:20PM +0900, Suwan Kim wrote:
> > > On Tue, Oct 22, 2019 at 12:28:39PM +0300, Dan Carpenter wrote:
> > > > tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> > > > head:   7d194c2100ad2a6dded545887d02754948ca5241
> > > > commit: ea44d190764b4422af4d1c29eaeb9e69e353b406 usbip: Implement SG support to vhci-hcd and stub driver
> > > > date:   7 weeks ago
> > > > 
> > > > If you fix the issue, kindly add following tag
> > > > Reported-by: kbuild test robot <lkp@intel.com>
> > > > Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
> > > > 
> > > > New smatch warnings:
> > > > drivers/usb/usbip/stub_rx.c:505 stub_recv_cmd_submit() error: uninitialized symbol 'nents'.
> > > > 
> > > > Old smatch warnings:
> > > > drivers/usb/usbip/stub_rx.c:450 stub_recv_xbuff() error: uninitialized symbol 'ret'.
> > > > 
> > > > # https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=ea44d190764b4422af4d1c29eaeb9e69e353b406
> > > > git remote add linus https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
> > > > git remote update linus
> > > > git checkout ea44d190764b4422af4d1c29eaeb9e69e353b406
> > > > vim +/nents +505 drivers/usb/usbip/stub_rx.c
> > > > 
> > > > 4d7b5c7f8ad49b drivers/staging/usbip/stub_rx.c Takahiro Hirofuchi 2008-07-09  453  static void stub_recv_cmd_submit(struct stub_device *sdev,
> > > > 4d7b5c7f8ad49b drivers/staging/usbip/stub_rx.c Takahiro Hirofuchi 2008-07-09  454  				 struct usbip_header *pdu)
> > > > 4d7b5c7f8ad49b drivers/staging/usbip/stub_rx.c Takahiro Hirofuchi 2008-07-09  455  {
> > > > 4d7b5c7f8ad49b drivers/staging/usbip/stub_rx.c Takahiro Hirofuchi 2008-07-09  456  	struct stub_priv *priv;
> > > > 4d7b5c7f8ad49b drivers/staging/usbip/stub_rx.c Takahiro Hirofuchi 2008-07-09  457  	struct usbip_device *ud = &sdev->ud;
> > > > 2d8f4595d1f275 drivers/staging/usbip/stub_rx.c Max Vozeler        2011-01-12  458  	struct usb_device *udev = sdev->udev;
> > > > ea44d190764b44 drivers/usb/usbip/stub_rx.c     Suwan Kim          2019-08-28  459  	struct scatterlist *sgl = NULL, *sg;
> > > > ea44d190764b44 drivers/usb/usbip/stub_rx.c     Suwan Kim          2019-08-28  460  	void *buffer = NULL;
> > > > ea44d190764b44 drivers/usb/usbip/stub_rx.c     Suwan Kim          2019-08-28  461  	unsigned long long buf_len;
> > > > ea44d190764b44 drivers/usb/usbip/stub_rx.c     Suwan Kim          2019-08-28  462  	int nents;
> > > > ea44d190764b44 drivers/usb/usbip/stub_rx.c     Suwan Kim          2019-08-28  463  	int num_urbs = 1;
> > > > c6688ef9f29762 drivers/usb/usbip/stub_rx.c     Shuah Khan         2017-12-07  464  	int pipe = get_pipe(sdev, pdu);
> > > > ea44d190764b44 drivers/usb/usbip/stub_rx.c     Suwan Kim          2019-08-28  465  	int use_sg = pdu->u.cmd_submit.transfer_flags & URB_DMA_MAP_SG;
> > > > ea44d190764b44 drivers/usb/usbip/stub_rx.c     Suwan Kim          2019-08-28  466  	int support_sg = 1;
> > > > ea44d190764b44 drivers/usb/usbip/stub_rx.c     Suwan Kim          2019-08-28  467  	int np = 0;
> > > > ea44d190764b44 drivers/usb/usbip/stub_rx.c     Suwan Kim          2019-08-28  468  	int ret, i;
> > > > 4d7b5c7f8ad49b drivers/staging/usbip/stub_rx.c Takahiro Hirofuchi 2008-07-09  469
> > > > 635f545a7e8be7 drivers/usb/usbip/stub_rx.c     Shuah Khan         2017-12-07  470  	if (pipe == -1)
> > > > 635f545a7e8be7 drivers/usb/usbip/stub_rx.c     Shuah Khan         2017-12-07  471  		return;
> > > > 4d7b5c7f8ad49b drivers/staging/usbip/stub_rx.c Takahiro Hirofuchi 2008-07-09  472
> > > > 4d7b5c7f8ad49b drivers/staging/usbip/stub_rx.c Takahiro Hirofuchi 2008-07-09  473  	priv = stub_priv_alloc(sdev, pdu);
> > > > 4d7b5c7f8ad49b drivers/staging/usbip/stub_rx.c Takahiro Hirofuchi 2008-07-09  474  	if (!priv)
> > > > 4d7b5c7f8ad49b drivers/staging/usbip/stub_rx.c Takahiro Hirofuchi 2008-07-09  475  		return;
> > > > 4d7b5c7f8ad49b drivers/staging/usbip/stub_rx.c Takahiro Hirofuchi 2008-07-09  476
> > > > ea44d190764b44 drivers/usb/usbip/stub_rx.c     Suwan Kim          2019-08-28  477  	buf_len = (unsigned long long)pdu->u.cmd_submit.transfer_buffer_length;
> > > > ea44d190764b44 drivers/usb/usbip/stub_rx.c     Suwan Kim          2019-08-28  478
> > > > ea44d190764b44 drivers/usb/usbip/stub_rx.c     Suwan Kim          2019-08-28  479  	/* allocate urb transfer buffer, if needed */
> > > > ea44d190764b44 drivers/usb/usbip/stub_rx.c     Suwan Kim          2019-08-28  480  	if (buf_len) {
> > > > ea44d190764b44 drivers/usb/usbip/stub_rx.c     Suwan Kim          2019-08-28  481  		if (use_sg) {
> > > > ea44d190764b44 drivers/usb/usbip/stub_rx.c     Suwan Kim          2019-08-28  482  			sgl = sgl_alloc(buf_len, GFP_KERNEL, &nents);
> > > > ea44d190764b44 drivers/usb/usbip/stub_rx.c     Suwan Kim          2019-08-28  483  			if (!sgl)
> > > > ea44d190764b44 drivers/usb/usbip/stub_rx.c     Suwan Kim          2019-08-28  484  				goto err_malloc;
> > > > ea44d190764b44 drivers/usb/usbip/stub_rx.c     Suwan Kim          2019-08-28  485  		} else {
> > > > ea44d190764b44 drivers/usb/usbip/stub_rx.c     Suwan Kim          2019-08-28  486  			buffer = kzalloc(buf_len, GFP_KERNEL);
> > > > ea44d190764b44 drivers/usb/usbip/stub_rx.c     Suwan Kim          2019-08-28  487  			if (!buffer)
> > > > ea44d190764b44 drivers/usb/usbip/stub_rx.c     Suwan Kim          2019-08-28  488  				goto err_malloc;
> > > > ea44d190764b44 drivers/usb/usbip/stub_rx.c     Suwan Kim          2019-08-28  489  		}
> > > > ea44d190764b44 drivers/usb/usbip/stub_rx.c     Suwan Kim          2019-08-28  490  	}
> > > > ea44d190764b44 drivers/usb/usbip/stub_rx.c     Suwan Kim          2019-08-28  491
> > > > ea44d190764b44 drivers/usb/usbip/stub_rx.c     Suwan Kim          2019-08-28  492  	/* Check if the server's HCD supports SG */
> > > > ea44d190764b44 drivers/usb/usbip/stub_rx.c     Suwan Kim          2019-08-28  493  	if (use_sg && !udev->bus->sg_tablesize) {
> > > > 
> > > > Smatch thinks "use_sg" can be true when "buf_len" is zero.  It's hard
> > > > to tell if Smatch is right or wrong without more context...
> > > 
> > > This is a bit strange. The meaning of "use_sg" is that client will
> > > use scatter-gather and client's urb->num_sgs is not zero. And buffer
> > > length should not be zero.
> > > 
> > > usb_sg and buf_len are both client-dependent variables, so I think
> > > if they have wrong value in the server side, the client must have
> > > sent use_sg and buf_len with incorrect values.
> > > 
> > > Did this error occur when compiling?
> > 
> > Smatch is doing static analysis, yes.
> > 
> > > If then, Did Smatch also consider vhci tx side?
> > 
> > I'm not really sure...  I can't reproduce the warning because on my
> > system Smatch doesn't parse usbip_recv() correctly so it ends up
> > silencing that warning.  :/
> > 
> 
> Hi Suwan,
> 
> This is a problem that needs fixing. nents
> 
>        /* allocate urb transfer buffer, if needed */
>         if (buf_len) {
>                 if (use_sg) {
>                         sgl = sgl_alloc(buf_len, GFP_KERNEL, &nents);
> 
> nents gets initialized here by sgl_alloc()
> 
>                         if (!sgl)
>                                 goto err_malloc;
>                 } else {
>                         buffer = kzalloc(buf_len, GFP_KERNEL);
>                         if (!buffer)
>                                 goto err_malloc;
>                 }
>         }
> 
>         /* Check if the server's HCD supports SG */
>         if (use_sg && !udev->bus->sg_tablesize) {
>                 /*
>                  * If the server's HCD doesn't support SG, break a single SG
>                  * request into several URBs and map each SG list entry to
>                  * corresponding URB buffer. The previously allocated SG
>                  * list is stored in priv->sgl (If the server's HCD support
> SG,
>                  * SG list is stored only in urb->sg) and it is used as an
>                  * indicator that the server split single SG request into
>                  * several URBs. Later, priv->sgl is used by stub_complete()
> and
>                  * stub_send_ret_submit() to reassemble the divied URBs.
>                  */
>                 support_sg = 0;
>                 num_urbs = nents;
> 
> I think nents will be valid here. Is there need for this additional
> check here? You can fold this into the previous use_sg check, right
> after the sg_alloc() success, I would think.

Or Is it your intention to check as follows?
I think this looks good.

	...
	int nents = 0

	...

	/* allocate urb transfer buffer, if needed */
	if (buf_len) {
		if (use_sg) {
			sgl = sgl_alloc(buf_len, GFP_KERNEL, &nents);
			if (!sgl)
				goto err_malloc;
		} else {
			buffer = kzalloc(buf_len, GFP_KERNEL);
			if (!buffer)
				goto err_malloc;
		}
	}

	/* Additional check here */
	if (use_sg && !nents) {
		err_message;
		goto err_urbs;
	}

	/* Check if the server's HCD supports SG */
	if (use_sg && !udev->bus->sg_tablesize) {

Regards,
Suwan Kim