On Thu, 25 Nov 2021, Dan Carpenter wrote:
> On Thu, Nov 25, 2021 at 03:07:37PM +0000, Lee Jones wrote:
> > On Thu, 25 Nov 2021, Dan Carpenter wrote:
> >
> > > On Thu, Nov 25, 2021 at 02:20:04PM +0000, Lee Jones wrote:
> > > > Supply additional checks in order to prevent unexpected results.
> > > >
> > > > Fixes: b892bf75b2034 ("ion: Switch ion to use dma-buf")
> > > > Signed-off-by: Lee Jones <lee.jones@xxxxxxxxxx>
> > > > ---
> > > > Should be back-ported from v4.9 and earlier.
> > > >
> > > > drivers/staging/android/ion/ion.c | 5 +++++
> > > > 1 file changed, 5 insertions(+)
> > > >
> > > > diff --git a/drivers/staging/android/ion/ion.c b/drivers/staging/android/ion/ion.c
> > > > index 806e9b30b9dc8..402b74f5d7e69 100644
> > > > --- a/drivers/staging/android/ion/ion.c
> > > > +++ b/drivers/staging/android/ion/ion.c
> > > > @@ -29,6 +29,7 @@
> > > > #include <linux/export.h>
> > > > #include <linux/mm.h>
> > > > #include <linux/mm_types.h>
> > > > +#include <linux/overflow.h>
> > > > #include <linux/rbtree.h>
> > > > #include <linux/slab.h>
> > > > #include <linux/seq_file.h>
> > > > @@ -509,6 +510,10 @@ static void *ion_handle_kmap_get(struct ion_handle *handle)
> > > > void *vaddr;
> > > >
> > > > if (handle->kmap_cnt) {
> > > > + if (check_add_overflow(handle->kmap_cnt,
> > > > + (unsigned int) 1, &handle->kmap_cnt))
> > > ^^^^^^^^^^^^^^^^^
> > >
> > > > + return ERR_PTR(-EOVERFLOW);
> > > > +
> > > > handle->kmap_cnt++;
> > > ^^^^^^^^^^^^^^^^^^^
> > > This will not do what you want at all. It's a double increment on the
> > > success path and it leave handle->kmap_cnt overflowed on failure path.
> >
> > I read the helper to take copies of the original variables.
> >
> > #define __unsigned_add_overflow(a, b, d) ({ \
> > typeof(a) __a = (a); \
> > typeof(b) __b = (b); \
> > typeof(d) __d = (d); \
> > (void) (&__a == &__b); \
> > (void) (&__a == __d); \
> > *__d = __a + __b; \
> ^^^^^^^^^^^^^^^^
> This assignment sets handle->kmap_cnt to the overflowed value.
>
> > *__d < __a; \
> > })
> >
> > Maybe I misread it.
> >
> > So the original patch [0] was better?
> >
> > [0] https://lore.kernel.org/stable/20211125120234.67987-1-lee.jones@xxxxxxxxxx/
>
> The original at least worked. :P
>
> You're catching me right as I'm knocking off for the day so I'm not
> sure how to write this code. I had thought that ->kmap_cnt was a
> regular int and not an unsigned int, but I would have to pull a stable
> tree to see where I misread the code.
>
> I'll look at this tomorrow Nairobi time, but I expect by then you'll
> already have it all figured out.
There's no rush. This has been broken for a long time.
--
Lee Jones [李琼斯]
Senior Technical Lead - Developer Services
Linaro.org │ Open source software for Arm SoCs
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