From: Florian Westphal <fw@xxxxxxxxx>
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: 84601d6ee68a ("bpf: add bpf_link support for BPF_NETFILTER programs")
Diagnosed-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Reported-by: Lai, Yi <yi1.lai@xxxxxxxxxxxxxxx>
Signed-off-by: Florian Westphal <fw@xxxxxxxxx>
Reviewed-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Signed-off-by: Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx>
---
net/netfilter/nf_bpf_link.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/net/netfilter/nf_bpf_link.c b/net/netfilter/nf_bpf_link.c
index 5257d5e7eb09..e5e79a08c10b 100644
--- a/net/netfilter/nf_bpf_link.c
+++ b/net/netfilter/nf_bpf_link.c
@@ -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);
}
--
2.30.2
