On Tue, Nov 23, 2021 at 12:27:19PM +0200, Nikolay Aleksandrov wrote:
> From: Nikolay Aleksandrov <nikolay@xxxxxxxxxx>
>
> When we try to add an IPv6 nexthop and IPv6 is not enabled
> (!CONFIG_IPV6) we'll hit a NULL pointer dereference[1] in the error path
> of nh_create_ipv6() due to calling ipv6_stub->fib6_nh_release. The bug
> has been present since the beginning of IPv6 nexthop gateway support.
> Commit 1aefd3de7bc6 ("ipv6: Add fib6_nh_init and release to stubs") tells
> us that only fib6_nh_init has a dummy stub because fib6_nh_release should
> not be called if fib6_nh_init returns an error, but the commit below added
> a call to ipv6_stub->fib6_nh_release in its error path. To fix it return
> the dummy stub's -EAFNOSUPPORT error directly without calling
> ipv6_stub->fib6_nh_release in nh_create_ipv6()'s error path.
[...]
> diff --git a/net/ipv4/nexthop.c b/net/ipv4/nexthop.c
> index a69a9e76f99f..5dbd4b5505eb 100644
> --- a/net/ipv4/nexthop.c
> +++ b/net/ipv4/nexthop.c
> @@ -2565,11 +2565,15 @@ static int nh_create_ipv6(struct net *net, struct nexthop *nh,
> /* sets nh_dev if successful */
> err = ipv6_stub->fib6_nh_init(net, fib6_nh, &fib6_cfg, GFP_KERNEL,
> extack);
> - if (err)
> + if (err) {
> + /* IPv6 is not enabled, don't call fib6_nh_release */
> + if (err == -EAFNOSUPPORT)
> + goto out;
> ipv6_stub->fib6_nh_release(fib6_nh);
Is the call actually necessary? If fib6_nh_init() failed, then I believe
it should clean up after itself and not rely on fib6_nh_release().
> - else
> + } else {
> nh->nh_flags = fib6_nh->fib_nh_flags;
> -
> + }
> +out:
> return err;
> }
>
> --
> 2.31.1
>
