On Mon, Dec 03, 2012 at 05:34:07PM +0100, Stefan Hajnoczi wrote:
> On Mon, Dec 3, 2012 at 2:20 PM, Laurent Navet <laurent.navet@xxxxxxxxx> wrote:
> > staging: line6: driver.c
> > The semantic patch that makes this output is available
> > in scripts/coccinelle/api/memdup.cocci.
> >
> > Signed-off-by: Laurent Navet <laurent.navet@xxxxxxxxx>
> > ---
> > drivers/staging/line6/driver.c | 5 ++---
> > 1 file changed, 2 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/staging/line6/driver.c b/drivers/staging/line6/driver.c
> > index f5c19b2..e1d6241 100644
> > --- a/drivers/staging/line6/driver.c
> > +++ b/drivers/staging/line6/driver.c
> > @@ -331,14 +331,13 @@ int line6_version_request_async(struct usb_line6 *line6)
> > char *buffer;
> > int retval;
> >
> > - buffer = kmalloc(sizeof(line6_request_version), GFP_ATOMIC);
> > + buffer = kmemdup(line6_request_version,
> > + sizeof(line6_request_version), GFP_ATOMIC);
> > if (buffer == NULL) {
> > dev_err(line6->ifcdev, "Out of memory");
> > return -ENOMEM;
> > }
> >
> > - memcpy(buffer, line6_request_version, sizeof(line6_request_version));
> > -
> > retval = line6_send_raw_message_async(line6, buffer,
> > sizeof(line6_request_version));
> > kfree(buffer);
> > --
> > 1.7.10.4
>
> Your change is fine but I'm not sure whether we should allocate memory
> in the first place:
>
> line6_send_raw_message_async() returns before the transfer is
> complete. It submits one or more URBs but I cannot see a guarantee
> that the buffer is no longer needed. It seems unsafe to kfree(buffer)
> before the request is complete.
>
As Greg pointed out we do need to allocate the memory to make DMA
work. But you're right that it is a use after free bug. We should
move the kfree(msg->buffer) to inside line6_async_request_sent().
I can send a fix for this tomorrow or if someone else wants to do it
while I'm sleeping that's fine too. :)
regards,
dan carpenter
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