Re: [PATCH] udmabuf: Fix a potential (and unlikely) access to unallocated memory

[Christophe JAILLET]

Le 18/09/2023 à 05:10, Gustavo A. R. Silva a écrit :
> On 9/18/23 12:46, Christophe JAILLET wrote:
> > If 'list_limit' is set to a very high value, 'lsize' computation could
> > overflow if 'head.count' is big enough.
> >
> > In such a case, udmabuf_create() will access to memory beyond 'list'.
> >
> > Use size_mul() to saturate the value, and have memdup_user() fail.
> >
> > Fixes: fbb0de795078 ("Add udmabuf misc device")
> > Signed-off-by: Christophe JAILLET <christophe.jaillet@xxxxxxxxxx>
> > ---
> >   drivers/dma-buf/udmabuf.c | 4 ++--
> >   1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
> > index c40645999648..fb4c4b5b3332 100644
> > --- a/drivers/dma-buf/udmabuf.c
> > +++ b/drivers/dma-buf/udmabuf.c
> > @@ -314,13 +314,13 @@ static long udmabuf_ioctl_create_list(struct 
> > file *filp, unsigned long arg)
> >       struct udmabuf_create_list head;
> >       struct udmabuf_create_item *list;
> >       int ret = -EINVAL;
> > -    u32 lsize;
> > +    size_t lsize;
> >       if (copy_from_user(&head, (void __user *)arg, sizeof(head)))
> >           return -EFAULT;
> >       if (head.count > list_limit)
> >           return -EINVAL;
> > -    lsize = sizeof(struct udmabuf_create_item) * head.count;
> > +    lsize = size_mul(sizeof(struct udmabuf_create_item), head.count);
> >       list = memdup_user((void __user *)(arg + sizeof(head)), lsize);
> >       if (IS_ERR(list))
> >           return PTR_ERR(list);
>
> How about this, and we get rid of `lsize`:

Keeping or removing lsize is mostly a matter of taste, I think.

Using sizeof(*list) is better.

Let see if there are some other comments, and I'll send a v2.

Thanks for the feed-back.

CJ

> diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
> index c40645999648..5cf9d849aaa8 100644
> --- a/drivers/dma-buf/udmabuf.c
> +++ b/drivers/dma-buf/udmabuf.c
> @@ -314,14 +314,13 @@ static long udmabuf_ioctl_create_list(struct file 
> *filp, unsigned long arg)
>          struct udmabuf_create_list head;
>          struct udmabuf_create_item *list;
>          int ret = -EINVAL;
> -       u32 lsize;
>
>          if (copy_from_user(&head, (void __user *)arg, sizeof(head)))
>                  return -EFAULT;
>          if (head.count > list_limit)
>                  return -EINVAL;
> -       lsize = sizeof(struct udmabuf_create_item) * head.count;
> -       list = memdup_user((void __user *)(arg + sizeof(head)), lsize);
> +       list = memdup_user((void __user *)(arg + sizeof(head)),
> +                          size_mul(sizeof(*list), head.count));
>          if (IS_ERR(list))
>                  return PTR_ERR(list);
>
>
> --
> Gustavo