[PATCH bpf v2] bpf: Fix netns reference imbalance in conntrack kfuncs
From: Chengfeng Ye
Date: Thu Jul 30 2026 - 04:33:01 EST
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
Snapshot every input field of opts with READ_ONCE() before validating or
using it. The netns_id snapshot keeps the namespace get/put pair
balanced, while the other snapshots keep the remaining options from
changing partway through an invocation. The individual reads can still
observe an inconsistent combination during a concurrent update, but each
selected field value remains stable for that invocation.
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 <nicoyip.dev@xxxxxxxxx>
---
Changes in v2:
- Snapshot l4proto, ct_zone_id, ct_zone_dir, and the reserved bytes in
addition to netns_id, as requested in review.
- Rebase onto current bpf/master.
Please queue this fix for stable kernels.
net/netfilter/nf_conntrack_bpf.c | 76 ++++++++++++++++++++++----------
1 file changed, 52 insertions(+), 24 deletions(-)
diff --git a/net/netfilter/nf_conntrack_bpf.c b/net/netfilter/nf_conntrack_bpf.c
index f98d1d4b42c3..c3395cb98c00 100644
--- a/net/netfilter/nf_conntrack_bpf.c
+++ b/net/netfilter/nf_conntrack_bpf.c
@@ -122,42 +122,56 @@ __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;
+ u16 ct_zone_id;
+ s32 netns_id;
+ u8 ct_zone_dir = 0;
+ u8 reserved[3] = {};
+ u8 l4proto;
int err;
if (!(opts_len == NF_BPF_CT_OPTS_SZ || opts_len == 12))
return ERR_PTR(-EINVAL);
+
+ netns_id = READ_ONCE(opts->netns_id);
+ l4proto = READ_ONCE(opts->l4proto);
+ ct_zone_id = READ_ONCE(opts->ct_zone_id);
if (opts_len == NF_BPF_CT_OPTS_SZ) {
- if (opts->reserved[0] || opts->reserved[1] || opts->reserved[2])
+ ct_zone_dir = READ_ONCE(opts->ct_zone_dir);
+ reserved[0] = READ_ONCE(opts->reserved[0]);
+ reserved[1] = READ_ONCE(opts->reserved[1]);
+ reserved[2] = READ_ONCE(opts->reserved[2]);
+ if (reserved[0] || reserved[1] || reserved[2])
return ERR_PTR(-EINVAL);
} else {
- if (opts->ct_zone_id)
+ if (ct_zone_id)
return ERR_PTR(-EINVAL);
}
- if (unlikely(opts->netns_id < BPF_F_CURRENT_NETNS))
+ if (unlikely(netns_id < BPF_F_CURRENT_NETNS))
return ERR_PTR(-EINVAL);
- err = bpf_nf_ct_tuple_parse(bpf_tuple, tuple_len, opts->l4proto,
+ err = bpf_nf_ct_tuple_parse(bpf_tuple, tuple_len, l4proto,
IP_CT_DIR_ORIGINAL, &otuple);
if (err < 0)
return ERR_PTR(err);
- err = bpf_nf_ct_tuple_parse(bpf_tuple, tuple_len, opts->l4proto,
+ err = bpf_nf_ct_tuple_parse(bpf_tuple, tuple_len, l4proto,
IP_CT_DIR_REPLY, &rtuple);
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);
}
if (opts_len == NF_BPF_CT_OPTS_SZ) {
- if (opts->ct_zone_dir == 0)
- opts->ct_zone_dir = NF_CT_DEFAULT_ZONE_DIR;
- nf_ct_zone_init(&ct_zone,
- opts->ct_zone_id, opts->ct_zone_dir, 0);
+ if (ct_zone_dir == 0) {
+ ct_zone_dir = NF_CT_DEFAULT_ZONE_DIR;
+ opts->ct_zone_dir = ct_zone_dir;
+ }
+ nf_ct_zone_init(&ct_zone, ct_zone_id, ct_zone_dir, 0);
} else {
ct_zone = nf_ct_zone_dflt;
}
@@ -171,7 +185,7 @@ __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;
@@ -186,46 +200,60 @@ 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;
+ u16 ct_zone_id;
+ s32 netns_id;
+ u8 ct_zone_dir = 0;
+ u8 reserved[3] = {};
+ u8 l4proto;
int err;
if (!opts || !bpf_tuple)
return ERR_PTR(-EINVAL);
if (!(opts_len == NF_BPF_CT_OPTS_SZ || opts_len == 12))
return ERR_PTR(-EINVAL);
+
+ netns_id = READ_ONCE(opts->netns_id);
+ l4proto = READ_ONCE(opts->l4proto);
+ ct_zone_id = READ_ONCE(opts->ct_zone_id);
if (opts_len == NF_BPF_CT_OPTS_SZ) {
- if (opts->reserved[0] || opts->reserved[1] || opts->reserved[2])
+ ct_zone_dir = READ_ONCE(opts->ct_zone_dir);
+ reserved[0] = READ_ONCE(opts->reserved[0]);
+ reserved[1] = READ_ONCE(opts->reserved[1]);
+ reserved[2] = READ_ONCE(opts->reserved[2]);
+ if (reserved[0] || reserved[1] || reserved[2])
return ERR_PTR(-EINVAL);
} else {
- if (opts->ct_zone_id)
+ if (ct_zone_id)
return ERR_PTR(-EINVAL);
}
- if (unlikely(opts->l4proto != IPPROTO_TCP && opts->l4proto != IPPROTO_UDP))
+ if (unlikely(l4proto != IPPROTO_TCP && l4proto != IPPROTO_UDP))
return ERR_PTR(-EPROTO);
- if (unlikely(opts->netns_id < BPF_F_CURRENT_NETNS))
+ if (unlikely(netns_id < BPF_F_CURRENT_NETNS))
return ERR_PTR(-EINVAL);
- err = bpf_nf_ct_tuple_parse(bpf_tuple, tuple_len, opts->l4proto,
+ err = bpf_nf_ct_tuple_parse(bpf_tuple, tuple_len, l4proto,
IP_CT_DIR_ORIGINAL, &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);
}
if (opts_len == NF_BPF_CT_OPTS_SZ) {
- if (opts->ct_zone_dir == 0)
- opts->ct_zone_dir = NF_CT_DEFAULT_ZONE_DIR;
- nf_ct_zone_init(&ct_zone,
- opts->ct_zone_id, opts->ct_zone_dir, 0);
+ if (ct_zone_dir == 0) {
+ ct_zone_dir = NF_CT_DEFAULT_ZONE_DIR;
+ opts->ct_zone_dir = ct_zone_dir;
+ }
+ nf_ct_zone_init(&ct_zone, ct_zone_id, ct_zone_dir, 0);
} else {
ct_zone = nf_ct_zone_dflt;
}
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