On Wed, 4 Oct 2006 10:14:05 -0400
Joe Korty <[email protected]> wrote:
> On Tue, Oct 03, 2006 at 04:39:36PM -0700, Andrew Morton wrote:
> > On Tue, 3 Oct 2006 08:16:27 -0700
> > Reinette Chatre <[email protected]> wrote:
> >
> > > lib/bitmap.c:bitmap_parse() is a library function that received as
> > > input a user buffer. This seemed to have originated from the way the
> > > write_proc function of the /proc filesystem operates.
> > >
> > > This function will be useful for other uses as well;
> > > for example, taking input for /sysfs instead of /proc,
> > > so it was changed to accept kernel buffers. We have this
> > > use for the Linux UWB project, as part as the upcoming
> > > bandwidth allocator code.
> > >
> > > Only a few routines used this function and they were changed too.
> >
> > Fair enough. But this: [ ... ] is sending us a message ;)
> >
> > How about adding a new bitmap_parse_user() (and cpumask_parse_user())
> > which does the above?
>
>
> I am slightly concerned about using a kmalloc where 'count' is specified
> by userspace. There might be a DoS attack in here somewhere.....
spose so. It would allow an unprivileged app to force lots of order-3
allocations, which can make page reclaim do a lot of work. Still...
> Perhaps we can reverse Andrew's idea: rename the existing bitmap_parse
> to bitmap_parse_user, then make the kernel-buffer version, bitmap_parse,
> be a wrapper around that.
>
I think we can do a version which omits the kmalloc altogether:
/*
* insert suitable comment here
*/
int bitmap_parse_kernel(const char *ubuf, unsigned int ubuflen,
unsigned long *maskp, int nmaskbits)
{
int c, old_c, totaldigits, ndigits, nchunks, nbits;
u32 chunk;
bitmap_zero(maskp, nmaskbits);
nchunks = nbits = totaldigits = c = 0;
do {
chunk = ndigits = 0;
/* Get the next chunk of the bitmap */
while (ubuflen) {
old_c = c;
if (__get_user(c, ubuf++))
return -EFAULT;
(Note the s/get_user/__get_user/)
int bitmap_parse_user(const char __user *ubuf, unsigned int ubuflen,
unsigned long *maskp, int nmaskbits)
{
if (!access_ok(VERIFY_READ, ubuf, ubuflen))
return -EFAULT;
return bitmap_parse_kernel((const char *)ubuf, ubuflen,
maskp, nmaskbits);
}
(Does typecasting a __user char * to a char * make sparse happy?)
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