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[45.78.65.84]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-31504cc73b6sm11245292eec.18.2026.07.29.09.31.49 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 29 Jul 2026 09:31:53 -0700 (PDT) From: Chengfeng Ye To: Pablo Neira Ayuso , Florian Westphal , Phil Sutter , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Alexei Starovoitov , Daniel Borkmann , Jesper Dangaard Brouer , John Fastabend , Stanislav Fomichev , Kumar Kartikeya Dwivedi , Lorenzo Bianconi Cc: netfilter-devel@vger.kernel.org, coreteam@netfilter.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org, Chengfeng Ye Subject: [PATCH bpf] bpf: Fix netns reference imbalance in conntrack kfuncs Date: Thu, 30 Jul 2026 00:31:41 +0800 Message-ID: <20260729163141.213611-1-nicoyip.dev@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit The opts argument of the BPF conntrack kfuncs can point to a shared map value. __bpf_nf_ct_lookup() and __bpf_nf_ct_alloc_entry() read opts->netns_id separately when acquiring and releasing the network namespace reference. The reference imbalance can occur as follows: CPU 0 CPU 1 read opts->netns_id (-1) skip get_net_ns_by_id() write opts->netns_id (id) read opts->netns_id (id) put_net(net) /* no matching get */ The reverse transition leaks the reference. Repeating the unmatched put can destroy a live namespace and crash later users. The kernel reported: Oops: general protection fault, probably for non-canonical address KASAN: null-ptr-deref in range [0x00000000000000e8-0x00000000000000ef] RIP: 0010:bpf_prog_test_run_xdp+0x52c/0x1700 Call Trace: __sys_bpf+0x1662/0x50c0 __x64_sys_bpf+0x73/0xb0 do_syscall_64+0xf9/0x540 entry_SYSCALL_64_after_hwframe+0x77/0x7f Kernel panic - not syncing: Fatal exception Read netns_id once with READ_ONCE() and use that value for validation and the matching get/put pair. Each invocation then consistently uses either the calling namespace or a referenced namespace. Fixes: aed8ee7feb44 ("net: netfilter: Deduplicate code in bpf_{xdp,skb}_ct_lookup") Fixes: d7e79c97c00c ("net: netfilter: Add kfuncs to allocate and insert CT") Signed-off-by: Chengfeng Ye --- Please queue this fix for stable kernels. net/netfilter/nf_conntrack_bpf.c | 20 ++++++++++++-------- 1 file changed, 12 insertions(+), 8 deletions(-) diff --git a/net/netfilter/nf_conntrack_bpf.c b/net/netfilter/nf_conntrack_bpf.c index f98d1d4b42c3..8b540846f299 100644 --- a/net/netfilter/nf_conntrack_bpf.c +++ b/net/netfilter/nf_conntrack_bpf.c @@ -122,6 +122,7 @@ __bpf_nf_ct_alloc_entry(struct net *net, struct bpf_sock_tuple *bpf_tuple, struct nf_conntrack_tuple otuple, rtuple; struct nf_conntrack_zone ct_zone; struct nf_conn *ct; + s32 netns_id; int err; if (!(opts_len == NF_BPF_CT_OPTS_SZ || opts_len == 12)) @@ -134,7 +135,8 @@ __bpf_nf_ct_alloc_entry(struct net *net, struct bpf_sock_tuple *bpf_tuple, return ERR_PTR(-EINVAL); } - if (unlikely(opts->netns_id < BPF_F_CURRENT_NETNS)) + netns_id = READ_ONCE(opts->netns_id); + if (unlikely(netns_id < BPF_F_CURRENT_NETNS)) return ERR_PTR(-EINVAL); err = bpf_nf_ct_tuple_parse(bpf_tuple, tuple_len, opts->l4proto, @@ -147,8 +149,8 @@ __bpf_nf_ct_alloc_entry(struct net *net, struct bpf_sock_tuple *bpf_tuple, if (err < 0) return ERR_PTR(err); - if (opts->netns_id >= 0) { - net = get_net_ns_by_id(net, opts->netns_id); + if (netns_id >= 0) { + net = get_net_ns_by_id(net, netns_id); if (unlikely(!net)) return ERR_PTR(-ENONET); } @@ -171,7 +173,7 @@ __bpf_nf_ct_alloc_entry(struct net *net, struct bpf_sock_tuple *bpf_tuple, __nf_ct_set_timeout(ct, timeout * HZ); out: - if (opts->netns_id >= 0) + if (netns_id >= 0) put_net(net); return ct; @@ -186,6 +188,7 @@ static struct nf_conn *__bpf_nf_ct_lookup(struct net *net, struct nf_conntrack_tuple tuple; struct nf_conntrack_zone ct_zone; struct nf_conn *ct; + s32 netns_id; int err; if (!opts || !bpf_tuple) @@ -201,7 +204,8 @@ static struct nf_conn *__bpf_nf_ct_lookup(struct net *net, } if (unlikely(opts->l4proto != IPPROTO_TCP && opts->l4proto != IPPROTO_UDP)) return ERR_PTR(-EPROTO); - if (unlikely(opts->netns_id < BPF_F_CURRENT_NETNS)) + netns_id = READ_ONCE(opts->netns_id); + if (unlikely(netns_id < BPF_F_CURRENT_NETNS)) return ERR_PTR(-EINVAL); err = bpf_nf_ct_tuple_parse(bpf_tuple, tuple_len, opts->l4proto, @@ -209,8 +213,8 @@ static struct nf_conn *__bpf_nf_ct_lookup(struct net *net, if (err < 0) return ERR_PTR(err); - if (opts->netns_id >= 0) { - net = get_net_ns_by_id(net, opts->netns_id); + if (netns_id >= 0) { + net = get_net_ns_by_id(net, netns_id); if (unlikely(!net)) return ERR_PTR(-ENONET); } @@ -225,7 +229,7 @@ static struct nf_conn *__bpf_nf_ct_lookup(struct net *net, } hash = nf_conntrack_find_get(net, &ct_zone, &tuple); - if (opts->netns_id >= 0) + if (netns_id >= 0) put_net(net); if (!hash) return ERR_PTR(-ENOENT); -- 2.43.0