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Date: Thu, 11 Mar 2010 14:20:34 +1100
From: Simon Horman <horms@...ge.net.au>
To: H Hartley Sweeten <hartleys@...ionengravers.com>
Cc: Linux Kernel <linux-kernel@...r.kernel.org>,
"greg@...ah.com" <greg@...ah.com>, "ss@....gov.au" <ss@....gov.au>
Subject: Re: [PATCH] staging/dt3155: make copy_{to/from}_user and put_user
typesafe
On Wed, Mar 10, 2010 at 06:19:32PM -0600, H Hartley Sweeten wrote:
> On Wednesday, March 10, 2010 5:01 PM, Simon Horman wrote:
> > On Thu, Mar 04, 2010 at 10:20:18AM -0700, H Hartley Sweeten wrote:
> >> This makes the kernel to user space data transfers typesafe and removes
> >> a number of unnecessary (void *) casts.
> >
> > Could you be more specific about what you mean by typesafe?
> > There still seem to be casts in there. Although fewer than before :-)
>
> >From include/asm-generic/uaccess.h
>
> static inline long copy_from_user(void *to,
> const void __user * from, unsigned long n)
> {
> might_sleep();
> if (access_ok(VERIFY_READ, from, n))
> return __copy_from_user(to, from, n);
> else
> return n;
> }
>
> static inline long copy_to_user(void __user *to,
> const void *from, unsigned long n)
> {
> might_sleep();
> if (access_ok(VERIFY_WRITE, to, n))
> return __copy_to_user(to, from, n);
> else
> return n;
> }
>
> >> Signed-off-by: H Hartley Sweeten <hsweeten@...ionengravers.com>
> >> Cc: Greg Kroah-Hartman <greg@...ah.com>
> >> Cc: Scott Smedley <ss@....gov.au>
> >>
> >> ---
> >>
> >> diff --git a/drivers/staging/dt3155/dt3155_drv.c b/drivers/staging/dt3155/dt3155_drv.c
> >> index a67c622..76c9d94 100644
> >> --- a/drivers/staging/dt3155/dt3155_drv.c
> >> +++ b/drivers/staging/dt3155/dt3155_drv.c
> >> @@ -528,6 +528,7 @@ static int dt3155_ioctl(struct inode *inode,
> >> unsigned long arg)
> >> {
> >> int minor = MINOR(inode->i_rdev); /* What device are we ioctl()'ing? */
> >> + void __user *up = (void __user *)arg;
>
> This cast is needed, and common, since 'arg' is passed as an unsigned long.
> The cast to __user memory space does not produce a sparse error.
>
> >>
> >> if ( minor >= MAXBOARDS || minor < 0 )
> >> return -ENODEV;
> >> @@ -554,7 +555,7 @@ static int dt3155_ioctl(struct inode *inode,
> >>
> >> {
> >> struct dt3155_config_s tmp;
> >> - if (copy_from_user((void *)&tmp, (void *) arg, sizeof(tmp)))
>
> The fist void * cast is unnecessary, the second produces a sparse warning
> since copy_from_user expects 'arg' to be a __user space pointer.
>
> >> + if (copy_from_user(&tmp, up, sizeof(tmp)))
>
> Using the 'up' (user pointer) variable quiets the warning and makes the
> function call typesafe (ok maybe that's the wrong term...).
>
> >> return -EFAULT;
> >> /* check for valid settings */
> >> if (tmp.rows > DT3155_MAX_ROWS ||
> >> @@ -572,8 +573,7 @@ static int dt3155_ioctl(struct inode *inode,
> >> }
> >> case DT3155_GET_CONFIG:
> >> {
> >> - if (copy_to_user((void *) arg, (void *) &dt3155_status[minor],
> >> - sizeof(dt3155_status_t) ))
>
> Here 'arg' should be a __user space pointer and the second cast is not
> necessary.
>
> >> + if (copy_to_user(up, &dt3155_status[minor], sizeof(dt3155_status_t)))
>
> Again, using 'up' fixes the sparse warning.
>
> The two below are the same.
>
> >> return -EFAULT;
> >> return 0;
> >> }
> >> @@ -593,8 +593,7 @@ static int dt3155_ioctl(struct inode *inode,
> >> return 0;
> >>
> >> quick_stop(minor);
> >> - if (copy_to_user((void *) arg, (void *) &dt3155_status[minor],
> >> - sizeof(dt3155_status_t)))
> >> + if (copy_to_user(up, &dt3155_status[minor], sizeof(dt3155_status_t)))
> >> return -EFAULT;
> >> return 0;
> >> }
> >> @@ -617,8 +616,7 @@ static int dt3155_ioctl(struct inode *inode,
> >> }
> >>
> >> dt3155_init_isr(minor);
> >> - if (copy_to_user( (void *) arg, (void *) &dt3155_status[minor],
> >> - sizeof(dt3155_status_t)))
> >> + if (copy_to_user(up, &dt3155_status[minor], sizeof(dt3155_status_t)))
> >> return -EFAULT;
> >> return 0;
> >> }
> >> @@ -819,11 +817,11 @@ static ssize_t dt3155_read(struct file *filep, char __user *buf,
> >> /* make this an offset */
> >> offset = frame_info_p->addr - dt3155_status[minor].mem_addr;
> >>
> >> - put_user(offset, (unsigned int *) buf);
> >> + put_user(offset, (unsigned int __user *)buf);
>
> For put_user, the second argument should be a __user pointer. 'buf' comes into the
> function correctly (char __user *) but needs the cast here so that the correct
> 'size' of data is copied to __user space. Same below.
>
> >> buf += sizeof(u32);
> >> - put_user( dt3155_status[minor].fbuffer.frame_count, (unsigned int *) buf);
> >> + put_user( dt3155_status[minor].fbuffer.frame_count, (unsigned int __user *)buf);
> >> buf += sizeof(u32);
> >> - put_user(dt3155_status[minor].state, (unsigned int *) buf);
> >> + put_user(dt3155_status[minor].state, (unsigned int __user *)buf);
> >> buf += sizeof(u32);
> >> if (copy_to_user(buf, frame_info_p, sizeof(frame_info_t)))
> >> return -EFAULT;
>
> All of this seems pretty common in other kernel code. And it removes a
> number of the sparse warnings generated by this file.
Hi,
thanks for the clarification. I agree that your patch is an improvement
and I don't see any problems with it (other than typesafe possibly being the
wrong term).
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