On Tue, 2020-10-27 at 17:58 +0100, Bartosz Golaszewski wrote:
> On Tue, Oct 27, 2020 at 5:50 PM Joe Perches <joe@xxxxxxxxxxx> wrote:
> >
> > On Tue, 2020-10-27 at 11:28 -0400, Michael S. Tsirkin wrote:
> > > On Tue, Oct 27, 2020 at 01:17:20PM +0100, Bartosz Golaszewski wrote:
> > > > From: Bartosz Golaszewski <bgolaszewski@xxxxxxxxxxxx>
> > > >
> > > > Use the helper that checks for overflows internally instead of manually
> > > > calculating the size of the new array.
> > > >
> > > > Signed-off-by: Bartosz Golaszewski <bgolaszewski@xxxxxxxxxxxx>
> > >
> > > No problem with the patch, it does introduce some symmetry in the code.
> >
> > Perhaps more symmetry by using kmemdup
> > ---
> > drivers/vhost/vringh.c | 23 ++++++++++-------------
> > 1 file changed, 10 insertions(+), 13 deletions(-)
> >
> > diff --git a/drivers/vhost/vringh.c b/drivers/vhost/vringh.c
> > index 8bd8b403f087..99222a3651cd 100644
> > --- a/drivers/vhost/vringh.c
> > +++ b/drivers/vhost/vringh.c
> > @@ -191,26 +191,23 @@ static int move_to_indirect(const struct vringh *vrh,
> > static int resize_iovec(struct vringh_kiov *iov, gfp_t gfp)
> > {
> > struct kvec *new;
> > - unsigned int flag, new_num = (iov->max_num & ~VRINGH_IOV_ALLOCATED) * 2;
> > + size_t new_num = (iov->max_num & ~VRINGH_IOV_ALLOCATED) * 2;
> > + size_t size;
> >
> > if (new_num < 8)
> > new_num = 8;
> >
> > - flag = (iov->max_num & VRINGH_IOV_ALLOCATED);
> > - if (flag)
> > - new = krealloc(iov->iov, new_num * sizeof(struct iovec), gfp);
> > - else {
> > - new = kmalloc_array(new_num, sizeof(struct iovec), gfp);
> > - if (new) {
> > - memcpy(new, iov->iov,
> > - iov->max_num * sizeof(struct iovec));
> > - flag = VRINGH_IOV_ALLOCATED;
> > - }
> > - }
> > + if (unlikely(check_mul_overflow(new_num, sizeof(struct iovec), &size)))
> > + return -ENOMEM;
> > +
>
> The whole point of using helpers such as kmalloc_array() is not doing
> these checks manually.
Tradeoffs for in readability for overflow and not mistyping or doing
the multiplication of iov->max_num * sizeof(struct iovec) twice.
Just fyi:
the realloc doesn't do a multiplication overflow test as written so the
suggestion is slightly more resistant to defect.
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