This commit adds support for enabling IP defrag using pre-existing
netfilter defrag support. Basically all the flag does is bump a refcnt
while the link the active. Checks are also added to ensure the prog
requesting defrag support is run _after_ netfilter defrag hooks.
We also take care to avoid any issues w.r.t. module unloading -- while
defrag is active on a link, the module is prevented from unloading.
Signed-off-by: Daniel Xu <dxu@xxxxxxxxx>
---
include/uapi/linux/bpf.h | 5 ++
net/netfilter/nf_bpf_link.c | 123 +++++++++++++++++++++++++++++----
tools/include/uapi/linux/bpf.h | 5 ++
3 files changed, 118 insertions(+), 15 deletions(-)
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 739c15906a65..12a5480314a2 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -1187,6 +1187,11 @@ enum bpf_perf_event_type {
*/
#define BPF_F_KPROBE_MULTI_RETURN (1U << 0)
+/* link_create.netfilter.flags used in LINK_CREATE command for
+ * BPF_PROG_TYPE_NETFILTER to enable IP packet defragmentation.
+ */
+#define BPF_F_NETFILTER_IP_DEFRAG (1U << 0)
+
/* When BPF ldimm64's insn[0].src_reg != 0 then this can have
* the following extensions:
*
diff --git a/net/netfilter/nf_bpf_link.c b/net/netfilter/nf_bpf_link.c
index c36da56d756f..8fe594bbc7e2 100644
--- a/net/netfilter/nf_bpf_link.c
+++ b/net/netfilter/nf_bpf_link.c
@@ -1,6 +1,8 @@
// SPDX-License-Identifier: GPL-2.0
#include <linux/bpf.h>
#include <linux/filter.h>
+#include <linux/kmod.h>
+#include <linux/module.h>
#include <linux/netfilter.h>
#include <net/netfilter/nf_bpf_link.h>
@@ -23,8 +25,88 @@ struct bpf_nf_link {
struct nf_hook_ops hook_ops;
struct net *net;
u32 dead;
+ const struct nf_defrag_hook *defrag_hook;
};
+static const struct nf_defrag_hook *
+get_proto_defrag_hook(struct bpf_nf_link *link,
+ const struct nf_defrag_hook __rcu *global_hook,
+ const char *mod)
+{
+ const struct nf_defrag_hook *hook;
+ int err;
+
+ /* RCU protects us from races against module unloading */
+ rcu_read_lock();
+ hook = rcu_dereference(global_hook);
+ if (!hook) {
+ rcu_read_unlock();
+ err = request_module(mod);
+ if (err)
+ return ERR_PTR(err < 0 ? err : -EINVAL);
+
+ rcu_read_lock();
+ hook = rcu_dereference(global_hook);
+ }
+
+ if (hook && try_module_get(hook->owner)) {
+ /* Once we have a refcnt on the module, we no longer need RCU */
+ hook = rcu_pointer_handoff(hook);
+ } else {
+ WARN_ONCE(!hook, "%s has bad registration", mod);
+ hook = ERR_PTR(-ENOENT);
+ }
+ rcu_read_unlock();
+
+ if (!IS_ERR(hook)) {
+ err = hook->enable(link->net);
+ if (err) {
+ module_put(hook->owner);
+ hook = ERR_PTR(err);
+ }
+ }
+
+ return hook;
+}
+
+static int bpf_nf_enable_defrag(struct bpf_nf_link *link)
+{
+ const struct nf_defrag_hook __maybe_unused *hook;
+
+ switch (link->hook_ops.pf) {
+#if IS_ENABLED(CONFIG_NF_DEFRAG_IPV4)
+ case NFPROTO_IPV4:
+ hook = get_proto_defrag_hook(link, nf_defrag_v4_hook, "nf_defrag_ipv4");
+ if (IS_ERR(hook))
+ return PTR_ERR(hook);
+
+ link->defrag_hook = hook;
+ return 0;
+#endif
+#if IS_ENABLED(CONFIG_NF_DEFRAG_IPV6)
+ case NFPROTO_IPV6:
+ hook = get_proto_defrag_hook(link, nf_defrag_v6_hook, "nf_defrag_ipv6");
+ if (IS_ERR(hook))
+ return PTR_ERR(hook);
+
+ link->defrag_hook = hook;
+ return 0;
+#endif
+ default:
+ return -EAFNOSUPPORT;
+ }
+}
+
+static void bpf_nf_disable_defrag(struct bpf_nf_link *link)
+{
+ const struct nf_defrag_hook *hook = link->defrag_hook;
+
+ if (!hook)
+ return;
+ hook->disable(link->net);
+ module_put(hook->owner);
+}
+
static void bpf_nf_link_release(struct bpf_link *link)
{
struct bpf_nf_link *nf_link = container_of(link, struct bpf_nf_link, link);
@@ -32,11 +114,11 @@ static void bpf_nf_link_release(struct bpf_link *link)
if (nf_link->dead)
return;
- /* prevent hook-not-found warning splat from netfilter core when
- * .detach was already called
- */
- if (!cmpxchg(&nf_link->dead, 0, 1))
+ /* do not double release in case .detach was already called */
+ if (!cmpxchg(&nf_link->dead, 0, 1)) {
nf_unregister_net_hook(nf_link->net, &nf_link->hook_ops);
+ bpf_nf_disable_defrag(nf_link);
+ }
}
static void bpf_nf_link_dealloc(struct bpf_link *link)
@@ -92,6 +174,8 @@ static const struct bpf_link_ops bpf_nf_link_lops = {
static int bpf_nf_check_pf_and_hooks(const union bpf_attr *attr)
{
+ int prio;
+
switch (attr->link_create.netfilter.pf) {
case NFPROTO_IPV4:
case NFPROTO_IPV6:
@@ -102,19 +186,18 @@ static int bpf_nf_check_pf_and_hooks(const union bpf_attr *attr)
return -EAFNOSUPPORT;
}
- if (attr->link_create.netfilter.flags)
+ if (attr->link_create.netfilter.flags & ~BPF_F_NETFILTER_IP_DEFRAG)
return -EOPNOTSUPP;
- /* make sure conntrack confirm is always last.
- *
- * In the future, if userspace can e.g. request defrag, then
- * "defrag_requested && prio before NF_IP_PRI_CONNTRACK_DEFRAG"
- * should fail.
- */
- switch (attr->link_create.netfilter.priority) {
- case NF_IP_PRI_FIRST: return -ERANGE; /* sabotage_in and other warts */
- case NF_IP_PRI_LAST: return -ERANGE; /* e.g. conntrack confirm */
- }
+ /* make sure conntrack confirm is always last */
+ prio = attr->link_create.netfilter.priority;
+ if (prio == NF_IP_PRI_FIRST)
+ return -ERANGE; /* sabotage_in and other warts */
+ else if (prio == NF_IP_PRI_LAST)
+ return -ERANGE; /* e.g. conntrack confirm */
+ else if ((attr->link_create.netfilter.flags & BPF_F_NETFILTER_IP_DEFRAG) &&
+ prio <= NF_IP_PRI_CONNTRACK_DEFRAG)
+ return -ERANGE; /* cannot use defrag if prog runs before nf_defrag */
return 0;
}
@@ -149,6 +232,7 @@ int bpf_nf_link_attach(const union bpf_attr *attr, struct bpf_prog *prog)
link->net = net;
link->dead = false;
+ link->defrag_hook = NULL;
err = bpf_link_prime(&link->link, &link_primer);
if (err) {
@@ -156,8 +240,17 @@ int bpf_nf_link_attach(const union bpf_attr *attr, struct bpf_prog *prog)
return err;
}
+ if (attr->link_create.netfilter.flags & BPF_F_NETFILTER_IP_DEFRAG) {
+ err = bpf_nf_enable_defrag(link);
+ if (err) {
+ bpf_link_cleanup(&link_primer);
+ return err;
+ }
+ }
+
err = nf_register_net_hook(net, &link->hook_ops);
if (err) {
+ bpf_nf_disable_defrag(link);
bpf_link_cleanup(&link_primer);
return err;
}
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 739c15906a65..12a5480314a2 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -1187,6 +1187,11 @@ enum bpf_perf_event_type {
*/
#define BPF_F_KPROBE_MULTI_RETURN (1U << 0)
+/* link_create.netfilter.flags used in LINK_CREATE command for
+ * BPF_PROG_TYPE_NETFILTER to enable IP packet defragmentation.
+ */
+#define BPF_F_NETFILTER_IP_DEFRAG (1U << 0)
+
/* When BPF ldimm64's insn[0].src_reg != 0 then this can have
* the following extensions:
*
--
2.41.0
