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netfilter: bpf: Support BPF_F_NETFILTER_IP_DEFRAG in netfilter link

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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@dxuuu.xyz>
Reviewed-by: Florian Westphal <fw@strlen.de>
Link: https://lore.kernel.org/r/5cff26f97e55161b7d56b09ddcf5f8888a5add1d.1689970773.git.dxu@dxuuu.xyz
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Daniel Xu 2023-07-21 14:22:46 -06:00 committed by Alexei Starovoitov
parent 9abddac583
commit 91721c2d02
3 changed files with 118 additions and 15 deletions
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5
include/uapi/linux/bpf.h
View File

@ -1188,6 +1188,11 @@ 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:
*

123
net/netfilter/nf_bpf_link.c
View File

@ -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;
}

5
tools/include/uapi/linux/bpf.h
View File

@ -1188,6 +1188,11 @@ 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:
*