[RFC nf-next v2 1/2] netfilter: bpf: support prog update

D. Wythe
2023-12-18T04:18:46Z

From: "D. Wythe" <alibuda@linux.alibaba.com>

To support the prog update, we need to ensure that the prog seen
within the hook is always valid. Considering that hooks are always
protected by rcu_read_lock(), which provide us the ability to
access the prog under rcu.

Signed-off-by: D. Wythe <alibuda@linux.alibaba.com>
---
net/netfilter/nf_bpf_link.c | 63 ++++++++++++++++++++++++++++++++++-----------
1 file changed, 48 insertions(+), 15 deletions(-)

diff --git a/net/netfilter/nf_bpf_link.c b/net/netfilter/nf_bpf_link.c
index e502ec0..8eed7cf 100644
--- a/net/netfilter/nf_bpf_link.c
+++ b/net/netfilter/nf_bpf_link.c
@@ -8,17 +8,8 @@
#include <net/netfilter/nf_bpf_link.h>
#include <uapi/linux/netfilter_ipv4.h>

-static unsigned int nf_hook_run_bpf(void *bpf_prog, struct sk_buff *skb,
- const struct nf_hook_state *s)
-{
- const struct bpf_prog *prog = bpf_prog;
- struct bpf_nf_ctx ctx = {
- .state = s,
- .skb = skb,
- };
-
- return bpf_prog_run(prog, &ctx);
-}
+/* protect link update in parallel */
+static DEFINE_MUTEX(bpf_nf_mutex);

struct bpf_nf_link {
struct bpf_link link;
@@ -26,8 +17,20 @@ struct bpf_nf_link {
struct net *net;
u32 dead;
const struct nf_defrag_hook *defrag_hook;
+ struct rcu_head head;
};

+static unsigned int nf_hook_run_bpf(void *bpf_link, struct sk_buff *skb,
+ const struct nf_hook_state *s)
+{
+ const struct bpf_nf_link *nf_link = bpf_link;
+ struct bpf_nf_ctx ctx = {
+ .state = s,
+ .skb = skb,
+ };
+ return bpf_prog_run(rcu_dereference(nf_link->link.prog), &ctx);
+}
+
#if IS_ENABLED(CONFIG_NF_DEFRAG_IPV4) || IS_ENABLED(CONFIG_NF_DEFRAG_IPV6)
static const struct nf_defrag_hook *
get_proto_defrag_hook(struct bpf_nf_link *link,
@@ -126,8 +129,7 @@ static void bpf_nf_link_release(struct bpf_link *link)
static void bpf_nf_link_dealloc(struct bpf_link *link)
{
struct bpf_nf_link *nf_link = container_of(link, struct bpf_nf_link, link);
-
- kfree(nf_link);
+ kfree_rcu(nf_link, head);
}

static int bpf_nf_link_detach(struct bpf_link *link)
@@ -162,7 +164,34 @@ static int bpf_nf_link_fill_link_info(const struct bpf_link *link,
static int bpf_nf_link_update(struct bpf_link *link, struct bpf_prog *new_prog,
struct bpf_prog *old_prog)
{
- return -EOPNOTSUPP;
+ struct bpf_nf_link *nf_link = container_of(link, struct bpf_nf_link, link);
+ int err = 0;
+
+ mutex_lock(&bpf_nf_mutex);
+
+ if (nf_link->dead) {
+ err = -EPERM;
+ goto out;
+ }
+
+ /* target old_prog mismatch */
+ if (old_prog && link->prog != old_prog) {
+ err = -EPERM;
+ goto out;
+ }
+
+ old_prog = link->prog;
+ if (old_prog == new_prog) {
+ /* don't need update */
+ bpf_prog_put(new_prog);
+ goto out;
+ }
+
+ old_prog = xchg(&link->prog, new_prog);
+ bpf_prog_put(old_prog);
+out:
+ mutex_unlock(&bpf_nf_mutex);
+ return err;
}

static const struct bpf_link_ops bpf_nf_link_lops = {
@@ -226,7 +255,11 @@ int bpf_nf_link_attach(const union bpf_attr *attr, struct bpf_prog *prog)

link->hook_ops.hook = nf_hook_run_bpf;
link->hook_ops.hook_ops_type = NF_HOOK_OP_BPF;
- link->hook_ops.priv = prog;
+
+ /* bpf_nf_link_release & bpf_nf_link_dealloc() can ensures that link remains
+ * valid at all times within nf_hook_run_bpf().
+ */
+ link->hook_ops.priv = link;

link->hook_ops.pf = attr->link_create.netfilter.pf;
link->hook_ops.priority = attr->link_create.netfilter.priority;
--
1.8.3.1