netdev - Re: [PATCH net] net: defer final 'struct net' free in netns dismantle

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Message-ID: <CANn89iLT6oAA-x+KX=sCAANBZKi1K52gOy-VW0hmofbO3GEhtw@mail.gmail.com>
Date: Tue, 3 Dec 2024 19:33:45 +0100
From: Eric Dumazet <edumazet@...gle.com>
To: Ilya Maximets <i.maximets@....org>
Cc: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org, eric.dumazet@...il.com, 
	Dan Streetman <dan.streetman@...onical.com>, 
	Steffen Klassert <steffen.klassert@...unet.com>
Subject: Re: [PATCH net] net: defer final 'struct net' free in netns dismantle

On Tue, Dec 3, 2024 at 7:23 PM Ilya Maximets <i.maximets@....org> wrote:
>
> On 12/3/24 17:50, Eric Dumazet wrote:
> > Ilya reported a slab-use-after-free in dst_destroy [1]
> >
> > Issue is in xfrm6_net_init() and xfrm4_net_init() :
> >
> > They copy xfrm[46]_dst_ops_template into net->xfrm.xfrm[46]_dst_ops.
> >
> > But net structure might be freed before all the dst callbacks are
> > called. So when dst_destroy() calls later :
> >
> > if (dst->ops->destroy)
> >     dst->ops->destroy(dst);
> >
> > dst->ops points to the old net->xfrm.xfrm[46]_dst_ops, which has been freed.
> >
> > See a relevant issue fixed in :
> >
> > ac888d58869b ("net: do not delay dst_entries_add() in dst_release()")
> >
> > A fix is to queue the 'struct net' to be freed after one
> > another cleanup_net() round (and existing rcu_barrier())
> >
> > [1]
>
> <snip>
>
> Hi, Eric.  Thanks for the patch!
>
> Though I tried to test it by applying directly on top of v6.12 tag, but I got
> the following UAF shortly after booting the kernel.  Seems like podman service
> was initializing something and creating namespaces for that.
>
> I can try applying the change on top of net tree, if that helps.
>
> Best regards, Ilya Maximets.

Oh right, a llist_for_each_entry_safe() should be better I think.

diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
index 2d98539f378ee4f1a9c0074381a155cff8024da3..70fea7c1a4b0a4fdbd0dd5d5acb7c6d786553996
100644
--- a/net/core/net_namespace.c
+++ b/net/core/net_namespace.c
@@ -448,12 +448,12 @@ static LLIST_HEAD(defer_free_list);
 static void net_complete_free(void)
 {
        struct llist_node *kill_list;
-       struct net *net;
+       struct net *net, *next;

        /* Get the list of namespaces to free from last round. */
        kill_list = llist_del_all(&defer_free_list);

-       llist_for_each_entry(net, kill_list, defer_free_list)
+       llist_for_each_entry_safe(net, next, kill_list, defer_free_list)
                kmem_cache_free(net_cachep, net);

 }