From: "D. Wythe" <alibuda@xxxxxxxxxxxxxxxxx>
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 use a
new RCU-protected context to access the prog.
Signed-off-by: D. Wythe <alibuda@xxxxxxxxxxxxxxxxx>
---
net/netfilter/nf_bpf_link.c | 124 +++++++++++++++++++++++++++++++++++++++-----
1 file changed, 111 insertions(+), 13 deletions(-)
diff --git a/net/netfilter/nf_bpf_link.c b/net/netfilter/nf_bpf_link.c
index e502ec0..918c470 100644
--- a/net/netfilter/nf_bpf_link.c
+++ b/net/netfilter/nf_bpf_link.c
@@ -8,17 +8,11 @@
#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)
+struct bpf_nf_hook_ctx
{
- const struct bpf_prog *prog = bpf_prog;
- struct bpf_nf_ctx ctx = {
- .state = s,
- .skb = skb,
- };
-
- return bpf_prog_run(prog, &ctx);
-}
+ struct bpf_prog *prog;
+ struct rcu_head rcu;
+};
struct bpf_nf_link {
struct bpf_link link;
@@ -26,8 +20,59 @@ struct bpf_nf_link {
struct net *net;
u32 dead;
const struct nf_defrag_hook *defrag_hook;
+ /* protect link update in parallel */
+ struct mutex update_lock;
+ struct bpf_nf_hook_ctx __rcu *hook_ctx;
};
+static struct bpf_nf_hook_ctx *
+bpf_nf_hook_ctx_from_prog(struct bpf_prog *prog, gfp_t flags)
+{
+ struct bpf_nf_hook_ctx *hook_ctx;
+
+ hook_ctx = kmalloc(sizeof(*hook_ctx), flags);
+ if (hook_ctx) {
+ hook_ctx->prog = prog;
+ bpf_prog_inc(prog);
+ }
+ return hook_ctx;
+}
+
+static void bpf_nf_hook_ctx_free(struct bpf_nf_hook_ctx *hook_ctx)
+{
+ if (!hook_ctx)
+ return;
+ if (hook_ctx->prog)
+ bpf_prog_put(hook_ctx->prog);
+ kfree(hook_ctx);
+}
+
+static void __bpf_nf_hook_ctx_free_rcu(struct rcu_head *head)
+{
+ struct bpf_nf_hook_ctx *hook_ctx = container_of(head, struct bpf_nf_hook_ctx, rcu);
+
+ bpf_nf_hook_ctx_free(hook_ctx);
+}
+
+static void bpf_nf_hook_ctx_free_rcu(struct bpf_nf_hook_ctx *hook_ctx)
+{
+ call_rcu(&hook_ctx->rcu, __bpf_nf_hook_ctx_free_rcu);
+}
+
+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 *link = bpf_link;
+ struct bpf_nf_hook_ctx *hook_ctx;
+ struct bpf_nf_ctx ctx = {
+ .state = s,
+ .skb = skb,
+ };
+
+ hook_ctx = rcu_dereference(link->hook_ctx);
+ return bpf_prog_run(hook_ctx->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,
@@ -120,6 +165,10 @@ 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);
+ /* Wait for outstanding hook to complete before the
+ * link gets released.
+ */
+ synchronize_rcu();
}
}
@@ -127,6 +176,7 @@ static void bpf_nf_link_dealloc(struct bpf_link *link)
{
struct bpf_nf_link *nf_link = container_of(link, struct bpf_nf_link, link);
+ bpf_nf_hook_ctx_free(nf_link->hook_ctx);
kfree(nf_link);
}
@@ -162,7 +212,42 @@ 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);
+ struct bpf_nf_hook_ctx *hook_ctx;
+ int err = 0;
+
+ mutex_lock(&nf_link->update_lock);
+
+ /* 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;
+ }
+
+ hook_ctx = bpf_nf_hook_ctx_from_prog(new_prog, GFP_USER);
+ if (!hook_ctx) {
+ err = -ENOMEM;
+ goto out;
+ }
+
+ /* replace and get the old one */
+ hook_ctx = rcu_replace_pointer(nf_link->hook_ctx, hook_ctx,
+ lockdep_is_held(&nf_link->update_lock));
+ /* free old hook_ctx */
+ bpf_nf_hook_ctx_free_rcu(hook_ctx);
+
+ old_prog = xchg(&link->prog, new_prog);
+ bpf_prog_put(old_prog);
+out:
+ mutex_unlock(&nf_link->update_lock);
+ return err;
}
static const struct bpf_link_ops bpf_nf_link_lops = {
@@ -222,11 +307,22 @@ int bpf_nf_link_attach(const union bpf_attr *attr, struct bpf_prog *prog)
if (!link)
return -ENOMEM;
+ link->hook_ctx = bpf_nf_hook_ctx_from_prog(prog, GFP_USER);
+ if (!link->hook_ctx) {
+ kfree(link);
+ return -ENOMEM;
+ }
+
bpf_link_init(&link->link, BPF_LINK_TYPE_NETFILTER, &bpf_nf_link_lops, 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() ensures that after its execution, there will be
+ * no ongoing or upcoming execution of nf_hook_run_bpf() within any context.
+ * Therefore, within nf_hook_run_bpf(), the link remains valid at all times."
+ */
+ link->hook_ops.priv = link;
link->hook_ops.pf = attr->link_create.netfilter.pf;
link->hook_ops.priority = attr->link_create.netfilter.priority;
@@ -236,9 +332,11 @@ int bpf_nf_link_attach(const union bpf_attr *attr, struct bpf_prog *prog)
link->dead = false;
link->defrag_hook = NULL;
+ mutex_init(&link->update_lock);
+
err = bpf_link_prime(&link->link, &link_primer);
if (err) {
- kfree(link);
+ bpf_nf_link_dealloc(&link->link);
return err;
}
--
1.8.3.1
