From: "D. Wythe" <[email protected]>
This patches attempt to implements updating of progs within
bpf netfilter link, allowing user update their ebpf netfilter
prog in hot update manner.
Besides, a corresponding test case has been added to verify
whether the update works.
--
v1:
1. remove unnecessary context, access the prog directly via rcu.
2. remove synchronize_rcu(), dealloc the nf_link via kfree_rcu.
3. check the dead flag during the update.
--
v1->v2:
1. remove unnecessary nf_prog, accessing nf_link->link.prog in direct.
--
v2->v3:
1. access nf_link->link.prog via rcu_dereference_raw to avoid warning.
D. Wythe (2):
netfilter: bpf: support prog update
selftests/bpf: Add netfilter link prog update test
net/netfilter/nf_bpf_link.c | 63 ++++++++++++----
.../bpf/prog_tests/netfilter_link_update_prog.c | 83 ++++++++++++++++++++++
.../bpf/progs/test_netfilter_link_update_prog.c | 24 +++++++
3 files changed, 155 insertions(+), 15 deletions(-)
create mode 100644 tools/testing/selftests/bpf/prog_tests/netfilter_link_update_prog.c
create mode 100644 tools/testing/selftests/bpf/progs/test_netfilter_link_update_prog.c
--
1.8.3.1
From: "D. Wythe" <[email protected]>
Update prog for active links and verify whether
the prog has been successfully replaced.
Expected output:
./test_progs -t netfilter_link_update_prog
Summary: 1/0 PASSED, 0 SKIPPED, 0 FAILED
Signed-off-by: D. Wythe <[email protected]>
---
.../bpf/prog_tests/netfilter_link_update_prog.c | 83 ++++++++++++++++++++++
.../bpf/progs/test_netfilter_link_update_prog.c | 24 +++++++
2 files changed, 107 insertions(+)
create mode 100644 tools/testing/selftests/bpf/prog_tests/netfilter_link_update_prog.c
create mode 100644 tools/testing/selftests/bpf/progs/test_netfilter_link_update_prog.c
diff --git a/tools/testing/selftests/bpf/prog_tests/netfilter_link_update_prog.c b/tools/testing/selftests/bpf/prog_tests/netfilter_link_update_prog.c
new file mode 100644
index 00000000..d23b544
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/netfilter_link_update_prog.c
@@ -0,0 +1,83 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include <test_progs.h>
+#include <linux/netfilter.h>
+#include <network_helpers.h>
+#include "test_netfilter_link_update_prog.skel.h"
+
+#define SERVER_ADDR "127.0.0.1"
+#define SERVER_PORT 12345
+
+static const char dummy_message[] = "A dummy message";
+
+static int send_dummy(int client_fd)
+{
+ struct sockaddr_storage saddr;
+ struct sockaddr *saddr_p;
+ socklen_t saddr_len;
+ int err;
+
+ saddr_p = (struct sockaddr *)&saddr;
+ err = make_sockaddr(AF_INET, SERVER_ADDR, SERVER_PORT, &saddr, &saddr_len);
+ if (!ASSERT_OK(err, "make_sockaddr"))
+ return -1;
+
+ err = sendto(client_fd, dummy_message, sizeof(dummy_message) - 1, 0, saddr_p, saddr_len);
+ if (!ASSERT_GE(err, 0, "sendto"))
+ return -1;
+
+ return 0;
+}
+
+void test_netfilter_link_update_prog(void)
+{
+ LIBBPF_OPTS(bpf_netfilter_opts, opts,
+ .pf = NFPROTO_IPV4,
+ .hooknum = NF_INET_LOCAL_OUT,
+ .priority = 100);
+ struct test_netfilter_link_update_prog *skel;
+ struct bpf_program *prog;
+ int server_fd, client_fd;
+ int err;
+
+ skel = test_netfilter_link_update_prog__open_and_load();
+ if (!ASSERT_OK_PTR(skel, "test_netfilter_link_update_prog__open_and_load"))
+ goto out;
+
+ prog = skel->progs.nf_link_prog;
+
+ if (!ASSERT_OK_PTR(prog, "load program"))
+ goto out;
+
+ skel->links.nf_link_prog = bpf_program__attach_netfilter(prog, &opts);
+ if (!ASSERT_OK_PTR(skel->links.nf_link_prog, "attach netfilter program"))
+ goto out;
+
+ server_fd = start_server(AF_INET, SOCK_DGRAM, SERVER_ADDR, SERVER_PORT, 0);
+ if (!ASSERT_GE(server_fd, 0, "start_server"))
+ goto out;
+
+ client_fd = connect_to_fd(server_fd, 0);
+ if (!ASSERT_GE(client_fd, 0, "connect_to_fd"))
+ goto out;
+
+ send_dummy(client_fd);
+
+ ASSERT_EQ(skel->bss->counter, 0, "counter should be zero");
+
+ err = bpf_link__update_program(skel->links.nf_link_prog, skel->progs.nf_link_prog_new);
+ if (!ASSERT_OK(err, "bpf_link__update_program"))
+ goto out;
+
+ send_dummy(client_fd);
+ ASSERT_GE(skel->bss->counter, 0, "counter should be greater than zero");
+out:
+ if (client_fd > 0)
+ close(client_fd);
+ if (server_fd > 0)
+ close(server_fd);
+
+ test_netfilter_link_update_prog__destroy(skel);
+}
+
+
diff --git a/tools/testing/selftests/bpf/progs/test_netfilter_link_update_prog.c b/tools/testing/selftests/bpf/progs/test_netfilter_link_update_prog.c
new file mode 100644
index 00000000..42ae332
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/test_netfilter_link_update_prog.c
@@ -0,0 +1,24 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+
+#define NF_ACCEPT 1
+
+SEC("netfilter")
+int nf_link_prog(struct bpf_nf_ctx *ctx)
+{
+ return NF_ACCEPT;
+}
+
+u64 counter = 0;
+
+SEC("netfilter")
+int nf_link_prog_new(struct bpf_nf_ctx *ctx)
+{
+ counter++;
+ return NF_ACCEPT;
+}
+
+char _license[] SEC("license") = "GPL";
+
--
1.8.3.1
From: "D. Wythe" <[email protected]>
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 <[email protected]>
---
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..9bc91d1 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_raw(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
On Wed, Dec 20, 2023 at 6:09 AM D. Wythe <[email protected]> wrote:
>
> From: "D. Wythe" <[email protected]>
>
> 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 <[email protected]>
> ---
> 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..9bc91d1 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;
I have to point out the same issues as before, but
will ask them differently...
Why do you think above rcu_head is necessary?
> };
>
> +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_raw(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);
Why is this needed ?
Have you looked at tcx_link_lops ?
> }
>
> 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);
Why do you need this mutex?
What race does it solve?
> +
> + 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
>
On 12/21/23 5:11 AM, Alexei Starovoitov wrote:
> On Wed, Dec 20, 2023 at 6:09 AM D. Wythe <[email protected]> wrote:
>> From: "D. Wythe" <[email protected]>
>>
>> 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 <[email protected]>
>> ---
>> 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..9bc91d1 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;
> I have to point out the same issues as before, but
> will ask them differently...
>
> Why do you think above rcu_head is necessary?
>
>> };
>>
>> +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_raw(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);
> Why is this needed ?
> Have you looked at tcx_link_lops ?
Introducing rcu_head/kfree_rcu is to address the situation where the
netfilter hooks might
still access the link after bpf_nf_link_dealloc.
nf_hook_run_bpf
const struct
bpf_nf_link *nf_link = bpf_link;
bpf_nf_link_release
nf_unregister_net_hook(nf_link->net, &nf_link->hook_ops);
bpf_nf_link_dealloc
free(link)
bpf_prog_run(link->prog);
I had checked the tcx_link_lops ,it's seems it use the synchronize_rcu()
to solve the
same problem, which is also the way we used in the first version.
https://lore.kernel.org/bpf/[email protected]/
However, we have received some opposing views, believing that this is a
bit overkill,
so we decided to use kfree_rcu.
https://lore.kernel.org/bpf/[email protected]/
>> }
>>
>> 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);
> Why do you need this mutex?
> What race does it solve?
To avoid user update a link with differ prog at the same time. I noticed
that sys_bpf()
doesn't seem to prevent being invoked by user at the same time. Have I
missed something?
Best wishes,
D. Wythe
>> +
>> + 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
>>
On Thu, Dec 21, 2023 at 11:06 PM D. Wythe <[email protected]> wrote:
>
>
>
> On 12/21/23 5:11 AM, Alexei Starovoitov wrote:
> > On Wed, Dec 20, 2023 at 6:09 AM D. Wythe <[email protected]> wrote:
> >> From: "D. Wythe" <[email protected]>
> >>
> >> 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 <[email protected]>
> >> ---
> >> 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..9bc91d1 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;
> > I have to point out the same issues as before, but
> > will ask them differently...
> >
> > Why do you think above rcu_head is necessary?
> >
> >> };
> >>
> >> +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_raw(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);
> > Why is this needed ?
> > Have you looked at tcx_link_lops ?
>
> Introducing rcu_head/kfree_rcu is to address the situation where the
> netfilter hooks might
> still access the link after bpf_nf_link_dealloc.
Why do you think so?
>
> nf_hook_run_bpf
> const struct
> bpf_nf_link *nf_link = bpf_link;
>
> bpf_nf_link_release
> nf_unregister_net_hook(nf_link->net, &nf_link->hook_ops);
>
> bpf_nf_link_dealloc
> free(link)
> bpf_prog_run(link->prog);
>
>
> I had checked the tcx_link_lops ,it's seems it use the synchronize_rcu()
> to solve the
Where do you see such code in tcx_link_lops ?
> same problem, which is also the way we used in the first version.
>
> https://lore.kernel.org/bpf/[email protected]/
>
> However, we have received some opposing views, believing that this is a
> bit overkill,
> so we decided to use kfree_rcu.
>
> https://lore.kernel.org/bpf/[email protected]/
>
> >> }
> >>
> >> 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);
> > Why do you need this mutex?
> > What race does it solve?
>
> To avoid user update a link with differ prog at the same time. I noticed
> that sys_bpf()
> doesn't seem to prevent being invoked by user at the same time. Have I
> missed something?
You're correct that sys_bpf() doesn't lock anything.
But what are you serializing in this bpf_nf_link_update() ?
What will happen if multiple bpf_nf_link_update()
without mutex run on different CPUs in parallel ?
On 12/23/23 6:23 AM, Alexei Starovoitov wrote:
> On Thu, Dec 21, 2023 at 11:06 PM D. Wythe <[email protected]> wrote:
>>
>>
>> On 12/21/23 5:11 AM, Alexei Starovoitov wrote:
>>> On Wed, Dec 20, 2023 at 6:09 AM D. Wythe <[email protected]> wrote:
>>>> From: "D. Wythe" <[email protected]>
>>>>
>>>> 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 <[email protected]>
>>>> ---
>>>> 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..9bc91d1 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;
>>> I have to point out the same issues as before, but
>>> will ask them differently...
>>>
>>> Why do you think above rcu_head is necessary?
>>>
>>>> };
>>>>
>>>> +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_raw(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);
>>> Why is this needed ?
>>> Have you looked at tcx_link_lops ?
>> Introducing rcu_head/kfree_rcu is to address the situation where the
>> netfilter hooks might
>> still access the link after bpf_nf_link_dealloc.
> Why do you think so?
>
Hi Alexei,
IMMO, nf_unregister_net_hook does not wait for the completion of the
execution of the hook that is being removed,
instead, it allocates a new array without the very hook to replace the
old arrayvia rcu_assign_pointer() (in __nf_hook_entries_try_shrink),
then it use call_rcu() to release the old one.
You can find more details in commit
8c873e2199700c2de7dbd5eedb9d90d5f109462b.
In other words, when nf_unregister_net_hook returns, there may still be
contexts executing hooks on the
old array, which means that the `link` may still be accessed after
nf_unregister_net_hook returns.
And that's the reason why we use kfree_rcu() to release the `link`.
>> nf_hook_run_bpf
>> const struct
>> bpf_nf_link *nf_link = bpf_link;
>>
>> bpf_nf_link_release
>> nf_unregister_net_hook(nf_link->net, &nf_link->hook_ops);
>>
>> bpf_nf_link_dealloc
>> free(link)
>> bpf_prog_run(link->prog);
>>
>>
>> I had checked the tcx_link_lops ,it's seems it use the synchronize_rcu()
>> to solve the
> Where do you see such code in tcx_link_lops ?
I'm not certain if the reason that it choose to use synchronize_rcu()is
the same as mine,
but I did see it here:
tcx_link_release() -> tcx_entry_sync()
static inline void tcx_entry_sync(void)
{
/* bpf_mprog_entry got a/b swapped, therefore ensure that
* there are no inflight users on the old one anymore.
*/
synchronize_rcu();
}
>> same problem, which is also the way we used in the first version.
>>
>> https://lore.kernel.org/bpf/[email protected]/
>>
>> However, we have received some opposing views, believing that this is a
>> bit overkill,
>> so we decided to use kfree_rcu.
>>
>> https://lore.kernel.org/bpf/[email protected]/
>>
>>>> }
>>>>
>>>> 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);
>>> Why do you need this mutex?
>>> What race does it solve?
>> To avoid user update a link with differ prog at the same time. I noticed
>> that sys_bpf()
>> doesn't seem to prevent being invoked by user at the same time. Have I
>> missed something?
> You're correct that sys_bpf() doesn't lock anything.
> But what are you serializing in this bpf_nf_link_update() ?
> What will happen if multiple bpf_nf_link_update()
> without mutex run on different CPUs in parallel ?
I must admit that it is indeed feasible if we eliminate the mutex and
use cmpxchg to swap the prog (we need to ensure that there is only one
bpf_prog_put() on the old prog).
However, when cmpxchg fails, it means that this context has not
outcompeted the other one, and we have to return a failure. Maybe
something like this:
if (!cmpxchg(&link->prog, old_prog, new_prog)) {
/* already replaced by another link_update */
return -xxx;
}
As a comparison, The version with the mutex wouldn't encounter this
error, every update would succeed. I think that it's too harsh for the
user to receive a failure
in that case since they haven't done anything wrong.
Best wishes,
D. Wythe
On Wed, Dec 27, 2023 at 12:20 AM D. Wythe <[email protected]> wrote:
>
>
> Hi Alexei,
>
>
> IMMO, nf_unregister_net_hook does not wait for the completion of the
> execution of the hook that is being removed,
> instead, it allocates a new array without the very hook to replace the
> old arrayvia rcu_assign_pointer() (in __nf_hook_entries_try_shrink),
> then it use call_rcu() to release the old one.
>
> You can find more details in commit
> 8c873e2199700c2de7dbd5eedb9d90d5f109462b.
>
> In other words, when nf_unregister_net_hook returns, there may still be
> contexts executing hooks on the
> old array, which means that the `link` may still be accessed after
> nf_unregister_net_hook returns.
>
> And that's the reason why we use kfree_rcu() to release the `link`.
> >> nf_hook_run_bpf
> >> const struct
> >> bpf_nf_link *nf_link = bpf_link;
> >>
> >> bpf_nf_link_release
> >> nf_unregister_net_hook(nf_link->net, &nf_link->hook_ops);
> >>
> >> bpf_nf_link_dealloc
> >> free(link)
> >> bpf_prog_run(link->prog);
Got it.
Sounds like it's an existing bug. If so it should be an independent
patch with Fixes tag.
Also please craft a test case to demonstrate UAF.
>
> I must admit that it is indeed feasible if we eliminate the mutex and
> use cmpxchg to swap the prog (we need to ensure that there is only one
> bpf_prog_put() on the old prog).
> However, when cmpxchg fails, it means that this context has not
> outcompeted the other one, and we have to return a failure. Maybe
> something like this:
>
> if (!cmpxchg(&link->prog, old_prog, new_prog)) {
> /* already replaced by another link_update */
> return -xxx;
> }
>
> As a comparison, The version with the mutex wouldn't encounter this
> error, every update would succeed. I think that it's too harsh for the
> user to receive a failure
> in that case since they haven't done anything wrong.
Disagree. The mutex doesn't prevent this issue.
There is always a race.
It happens when link_update.old_prog_fd and BPF_F_REPLACE
were specified.
One user space passes an FD of the old prog and
another user space doing the same. They both race and one of them
gets
if (old_prog && link->prog != old_prog) {
err = -EPERM;
it's no different with dropping the mutex and doing:
if (old_prog) {
if (!cmpxchg(&link->prog, old_prog, new_prog))
-EPERM
} else {
old_prog = xchg(&link->prog, new_prog);
}
On 12/28/23 3:00 AM, Alexei Starovoitov wrote:
> On Wed, Dec 27, 2023 at 12:20 AM D. Wythe <[email protected]> wrote:
>>
>> Hi Alexei,
>>
>>
>> IMMO, nf_unregister_net_hook does not wait for the completion of the
>> execution of the hook that is being removed,
>> instead, it allocates a new array without the very hook to replace the
>> old arrayvia rcu_assign_pointer() (in __nf_hook_entries_try_shrink),
>> then it use call_rcu() to release the old one.
>>
>> You can find more details in commit
>> 8c873e2199700c2de7dbd5eedb9d90d5f109462b.
>>
>> In other words, when nf_unregister_net_hook returns, there may still be
>> contexts executing hooks on the
>> old array, which means that the `link` may still be accessed after
>> nf_unregister_net_hook returns.
>>
>> And that's the reason why we use kfree_rcu() to release the `link`.
>>>> nf_hook_run_bpf
>>>> const struct
>>>> bpf_nf_link *nf_link = bpf_link;
>>>>
>>>> bpf_nf_link_release
>>>> nf_unregister_net_hook(nf_link->net, &nf_link->hook_ops);
>>>>
>>>> bpf_nf_link_dealloc
>>>> free(link)
>>>> bpf_prog_run(link->prog);
> Got it.
> Sounds like it's an existing bug. If so it should be an independent
> patch with Fixes tag.
>
> Also please craft a test case to demonstrate UAF.
>
It is not an existing bug... Accessing the link within the hook was
something I introduced here
to support updates????, as previously there was no access to the link
within the hook.
>> I must admit that it is indeed feasible if we eliminate the mutex and
>> use cmpxchg to swap the prog (we need to ensure that there is only one
>> bpf_prog_put() on the old prog).
>> However, when cmpxchg fails, it means that this context has not
>> outcompeted the other one, and we have to return a failure. Maybe
>> something like this:
>>
>> if (!cmpxchg(&link->prog, old_prog, new_prog)) {
>> /* already replaced by another link_update */
>> return -xxx;
>> }
>>
>> As a comparison, The version with the mutex wouldn't encounter this
>> error, every update would succeed. I think that it's too harsh for the
>> user to receive a failure
>> in that case since they haven't done anything wrong.
> Disagree. The mutex doesn't prevent this issue.
> There is always a race.
> It happens when link_update.old_prog_fd and BPF_F_REPLACE
> were specified.
> One user space passes an FD of the old prog and
> another user space doing the same. They both race and one of them
> gets
> if (old_prog && link->prog != old_prog) {
> err = -EPERM;
>
> it's no different with dropping the mutex and doing:
> if (old_prog) {
> if (!cmpxchg(&link->prog, old_prog, new_prog))
> -EPERM
> } else {
> old_prog = xchg(&link->prog, new_prog);
> }
Got it! It's very helpful, Thanks very much! I will modify my patch
accordingly.
Best wishes,
D. Wythe