Commit 1230fe7a authored Oct 10, 2024 by Florian Westphal Committed by Pablo Neira Ayuso Oct 17, 2024

netfilter: bpf: must hold reference on net namespace



BUG: KASAN: slab-use-after-free in __nf_unregister_net_hook+0x640/0x6b0
Read of size 8 at addr ffff8880106fe400 by task repro/72=
bpf_nf_link_release+0xda/0x1e0
bpf_link_free+0x139/0x2d0
bpf_link_release+0x68/0x80
__fput+0x414/0xb60

Eric says:
 It seems that bpf was able to defer the __nf_unregister_net_hook()
 after exit()/close() time.
 Perhaps a netns reference is missing, because the netns has been
 dismantled/freed already.
 bpf_nf_link_attach() does :
 link->net = net;
 But I do not see a reference being taken on net.

Add such a reference and release it after hook unreg.
Note that I was unable to get syzbot reproducer to work, so I
do not know if this resolves this splat.

Fixes: 84601d6e ("bpf: add bpf_link support for BPF_NETFILTER programs")
Diagnosed-by: Eric Dumazet <edumazet@google.com>
Reported-by: Lai, Yi <yi1.lai@linux.intel.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

parent cb560795

net/netfilter/nf_bpf_link.c

+4 −0

Original line number	Diff line number	Diff line
		@@ -23,6 +23,7 @@ static unsigned int nf_hook_run_bpf(void bpf_prog, struct sk_buff skb,
		struct bpf_nf_link {
		struct bpf_link link;
		struct nf_hook_ops hook_ops;
		netns_tracker ns_tracker;
		struct net *net;
		u32 dead;
		const struct nf_defrag_hook *defrag_hook;
		@@ -120,6 +121,7 @@ static void bpf_nf_link_release(struct bpf_link *link)
		if (!cmpxchg(&nf_link->dead, 0, 1)) {
		nf_unregister_net_hook(nf_link->net, &nf_link->hook_ops);
		bpf_nf_disable_defrag(nf_link);
		put_net_track(nf_link->net, &nf_link->ns_tracker);
		}
		}

		@@ -257,6 +259,8 @@ int bpf_nf_link_attach(const union bpf_attr attr, struct bpf_prog prog)
		return err;
		}

		get_net_track(net, &link->ns_tracker, GFP_KERNEL);

		return bpf_link_settle(&link_primer);
		}