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SubjectRe: [PATCH] uverbs: prevent potential underflow
On Tue, Oct 08, 2019 at 04:44:25PM -0300, Jason Gunthorpe wrote:
> On Sat, Oct 05, 2019 at 08:23:37AM +0300, Dan Carpenter wrote:
> > The issue is in drivers/infiniband/core/uverbs_std_types_cq.c in the
> > UVERBS_HANDLER(UVERBS_METHOD_CQ_CREATE) function. We check that:
> >
> > if (attr.comp_vector >= attrs->ufile->device->num_comp_vectors) {
> >
> > But we don't check that "attr.comp_vector" whether negative. It
> > could potentially lead to an array underflow. My concern would be where
> > cq->vector is used in the create_cq() function from the cxgb4 driver.
> >
> > Fixes: 9ee79fce3642 ("IB/core: Add completion queue (cq) object actions")
> > Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> > ---
> > drivers/infiniband/core/uverbs.h | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
>
>
> > diff --git a/drivers/infiniband/core/uverbs.h b/drivers/infiniband/core/uverbs.h
> > index 1e5aeb39f774..63f7f7db5902 100644
> > --- a/drivers/infiniband/core/uverbs.h
> > +++ b/drivers/infiniband/core/uverbs.h
> > @@ -98,7 +98,7 @@ ib_uverbs_init_udata_buf_or_null(struct ib_udata *udata,
> >
> > struct ib_uverbs_device {
> > atomic_t refcount;
> > - int num_comp_vectors;
> > + u32 num_comp_vectors;
> > struct completion comp;
> > struct device dev;
> > /* First group for device attributes, NULL terminated array */
>
> I would have expected you to change struct ib_cq_init_attr ? Or at
> least both..
>
> This is actually a bug as the type of
> UVERBS_ATTR_CREATE_CQ_COMP_VECTOR for userspace is u32:
>
> UVERBS_ATTR_PTR_IN(UVERBS_ATTR_CREATE_CQ_COMP_VECTOR,
> UVERBS_ATTR_TYPE(u32),
> UA_MANDATORY),
>
> But we are stuffing it into a int:
>
> ret = uverbs_copy_from(&attr.comp_vector, attrs,
> UVERBS_ATTR_CREATE_CQ_COMP_VECTOR);
>
> So very large values will become negative and switching
> num_comp_vectors to u32 won't help??

Yeah. You're right. I should have changed both. I'm not sure what I
was thinking.

My patch does fix the bug because of type promotion, but we should
change both to u32.

regards,
dan carpenter

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