Messages in this thread | | | Date | Wed, 30 Sep 2009 15:20:11 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH 8/9] Add explicit bound checks in mm/migrate.c |
| |
On Sat, 26 Sep 2009 20:54:06 +0200 Arjan van de Ven <arjan@infradead.org> wrote:
> From: Arjan van de Ven <arjan@linux.intel.com> > Subject: [PATCH 8/9] Add explicit bound checks in mm/migrate.c > CC: akpm@linux-foundation.org > > The memory migration code has some curious copy_from_user bounds, > that are likely ok, but are not immediately obvious to me or to GCC. > > This patch adds a simple explicit bound check; this allows GCC > and me to be more assured that the copy_from_user will never overwrite > its destination buffer.
I don't really see what's being fixed here. The original code seems straightforward and safe enough?
The identifier `chunk_nr' is a bit ambiguous. Is it "number of chunks" or is it "index of this chunk"?
> > diff --git a/mm/migrate.c b/mm/migrate.c > index 1a4bf48..5b9ebc5 100644 > --- a/mm/migrate.c > +++ b/mm/migrate.c > @@ -1044,11 +1044,15 @@ static int do_pages_stat(struct mm_struct *mm, unsigned long nr_pages, > int err; > > for (i = 0; i < nr_pages; i += chunk_nr) { > + unsigned int copy; > if (chunk_nr + i > nr_pages) > chunk_nr = nr_pages - i;
A newline after end-of-locals is conventional.
`i' and `chunk_nr' have type `unsigned long' and you're mixing that up with `unsigned int'.
> - err = copy_from_user(chunk_pages, &pages[i], > - chunk_nr * sizeof(*chunk_pages));
And we mix it up with size_t as well.
The type choices are a bit confused and sloppy. Converting it all to `unsigned int' should be OK.
> + copy = chunk_nr * sizeof(*chunk_pages); > + if (copy > DO_PAGES_STAT_CHUNK_NR) > + return -EFAULT; > + > + err = copy_from_user(chunk_pages, &pages[i], copy); > if (err) { > err = -EFAULT; > goto out;
| |