Patch "netfilter: bpf: must hold reference on net namespace" has been added to the 6.6-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    netfilter: bpf: must hold reference on net namespace

to the 6.6-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     netfilter-bpf-must-hold-reference-on-net-namespace.patch
and it can be found in the queue-6.6 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 273be4ceb2ca5d9a2e2f72351181f37cad162ea4
Author: Florian Westphal <fw@xxxxxxxxx>
Date:   Thu Oct 10 18:34:05 2024 +0200

    netfilter: bpf: must hold reference on net namespace
    
    [ Upstream commit 1230fe7ad3974f7bf6c78901473e039b34d4fb1f ]
    
    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>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/net/netfilter/nf_bpf_link.c b/net/netfilter/nf_bpf_link.c
index 96015a59db09e..2aad0562a4135 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);
 	}
 }
 
@@ -258,6 +260,8 @@ 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);
 }