Re: [PATCH net] can: raw: fix raw_rcv panic for sock UAF

[Oliver Hartkopp]

On 21.07.21 13:37, Ziyang Xuan (William) wrote:
> On 7/21/2021 5:24 PM, Oliver Hartkopp wrote:

> > Can you please resend the below patch as suggested by Greg KH and add my
> >
> > Signed-off-by: Oliver Hartkopp <socketcan@xxxxxxxxxxxx>
> >
> > as it also adds the dev_get_by_index() return check.
> >
> > diff --git a/net/can/raw.c b/net/can/raw.c
> > index ed4fcb7ab0c3..d3cbc32036c7 100644
> > --- a/net/can/raw.c
> > +++ b/net/can/raw.c
> > @@ -544,14 +544,18 @@ static int raw_setsockopt(struct socket *sock, int level, int optname,
> >           } else if (count == 1) {
> >               if (copy_from_sockptr(&sfilter, optval, sizeof(sfilter)))
> >                   return -EFAULT;
> >           }
> >
> > +        rtnl_lock();
> >           lock_sock(sk);
> >
> > -        if (ro->bound && ro->ifindex)
> > +        if (ro->bound && ro->ifindex) {
> >               dev = dev_get_by_index(sock_net(sk), ro->ifindex);
> > +            if (!dev)
> > +                goto out_fil;
> > +        }
> At first, I also use this modification. After discussion with my partner, we found that
> it is impossible scenario if we use rtnl_lock to protect net_device object.
> We can see two sequences:
> 1. raw_setsockopt first get rtnl_lock, unregister_netdevice_many later.
> It can be simplified to add the filter in raw_setsockopt, then remove the filter in raw_notify.
>
> 2. unregister_netdevice_many first get rtnl_lock, raw_setsockopt later.
> raw_notify will set ro->ifindex, ro->bound and ro->count to zero firstly. The filter will not
> be added to any filter_list in raw_notify.
>
> So I selected the current modification. Do you think so?
>
> My first modification as following:
>
> diff --git a/net/can/raw.c b/net/can/raw.c
> index ed4fcb7ab0c3..a0ce4908317f 100644
> --- a/net/can/raw.c
> +++ b/net/can/raw.c
> @@ -546,10 +546,16 @@ static int raw_setsockopt(struct socket *sock, int level, int optname,
>                                  return -EFAULT;
>                  }
>
> +               rtnl_lock();
>                  lock_sock(sk);
>
> -               if (ro->bound && ro->ifindex)
> +               if (ro->bound && ro->ifindex) {
>                          dev = dev_get_by_index(sock_net(sk), ro->ifindex);
> +                       if (!dev) {
> +                               err = -ENODEV;
> +                               goto out_fil;
> +                       }
> +               }
>
>                  if (ro->bound) {
>                          /* (try to) register the new filters */
> @@ -559,11 +565,8 @@ static int raw_setsockopt(struct socket *sock, int level, int optname,
>                          else
>                                  err = raw_enable_filters(sock_net(sk), dev, sk,
>                                                           filter, count);
> -                       if (err) {
> -                               if (count > 1)
> -                                       kfree(filter);
> +                       if (err)
>                                  goto out_fil;
> -                       }
>
>                          /* remove old filter registrations */
>                          raw_disable_filters(sock_net(sk), dev, sk, ro->filter,
> @@ -584,10 +587,14 @@ static int raw_setsockopt(struct socket *sock, int level, int optname,
>                  ro->count  = count;
>
>    out_fil:
> +               if (err && count > 1)
> +                       kfree(filter);
> +

Setting the err variable to -ENODEV is a good idea but I do not like the 
movement of kfree(filter).

The kfree() has a tight relation inside the if-statement for ro->bound 
which makes it easier to understand.

Regards,
Oliver

ps. your patches have less context than mine. Do you have different 
settings for -U<n>, --unified=<n> for 'git diff' ?

>                  if (dev)
>                          dev_put(dev);
>
>                  release_sock(sk);
> +               rtnl_unlock();
>
>                  break;
>
> @@ -600,10 +607,16 @@ static int raw_setsockopt(struct socket *sock, int level, int optname,
>
>                  err_mask &= CAN_ERR_MASK;
>
> +               rtnl_lock();
>                  lock_sock(sk);
>
> -               if (ro->bound && ro->ifindex)
> +               if (ro->bound && ro->ifindex) {
>                          dev = dev_get_by_index(sock_net(sk), ro->ifindex);
> +                       if (!dev) {
> +                               err = -ENODEV;
> +                               goto out_err;
> +                       }
> +               }
>
>                  /* remove current error mask */
>                  if (ro->bound) {
> @@ -627,6 +640,7 @@ static int raw_setsockopt(struct socket *sock, int level, int optname,
>                          dev_put(dev);
>
>                  release_sock(sk);
> +               rtnl_unlock();
>
>                  break;