Re: drivers/usb/usbip/stub_rx.c:505 stub_recv_cmd_submit() error: uninitialized symbol 'nents'.

From: Suwan Kim
Date: Fri Nov 01 2019 - 10:34:48 EST

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On Tue, Oct 29, 2019 at 05:07:58AM -0600, shuah wrote:
> On 10/25/19 9:40 PM, Suwan Kim wrote:
> > 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@xxxxxxxxx>
> > > > > > Reported-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
> > > > > >
> > > > > > 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;
>
> Why can't we move the
> > /* Check if the server's HCD supports SG */
> > if (use_sg && !udev->bus->sg_tablesize) {
> >
>
> under this check?

I understood. Moving this check after sgl_alloc() does not seem to
require any additional checks on nents.

But I think we need to check for the case that Smatch reported that
use_sg is true and buf_len is zero.

If there is no error check and an error condition occurs, the URB
will be passed to the next step without a buffer.

I attached the code. If you are okay, I will send a patch.

Regards,
Suwan Kim

---
diff --git a/drivers/usb/usbip/stub_rx.c b/drivers/usb/usbip/stub_rx.c
index 66edfeea68fe..0b6c4736ffd6 100644
--- a/drivers/usb/usbip/stub_rx.c
+++ b/drivers/usb/usbip/stub_rx.c
@@ -476,12 +476,39 @@ static void stub_recv_cmd_submit(struct stub_device *sdev,

buf_len = (unsigned long long)pdu->u.cmd_submit.transfer_buffer_length;

+ if (use_sg && !buf_len) {
+ dev_err(&udev->dev, "sg buffer with zero length\n");
+ goto err_malloc;
+ }
+
/* 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;
+
+ /* Check if the server's HCD supports SG */
+ if (!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;
+ priv->completed_urbs = 0;
+ pdu->u.cmd_submit.transfer_flags &=
+ ~URB_DMA_MAP_SG;
+ }
} else {
buffer = kzalloc(buf_len, GFP_KERNEL);
if (!buffer)
@@ -489,24 +516,6 @@ static void stub_recv_cmd_submit(struct stub_device *sdev,
}
}

- /* 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;
- priv->completed_urbs = 0;
- pdu->u.cmd_submit.transfer_flags &= ~URB_DMA_MAP_SG;
- }
-
/* allocate urb array */
priv->num_urbs = num_urbs;
priv->urbs = kmalloc_array(num_urbs, sizeof(*priv->urbs), GFP_KERNEL);

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