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.
Reviewed-by: Florian Westphal <[email protected]>
Signed-off-by: Daniel Xu <[email protected]>
---
include/uapi/linux/bpf.h | 5 ++
net/netfilter/nf_bpf_link.c | 129 ++++++++++++++++++++++++++++++---
tools/include/uapi/linux/bpf.h | 5 ++
3 files changed, 128 insertions(+), 11 deletions(-)
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 600d0caebbd8..c820076c38db 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -1180,6 +1180,11 @@ 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..5b72aa246577 100644
--- a/net/netfilter/nf_bpf_link.c
+++ b/net/netfilter/nf_bpf_link.c
@@ -1,6 +1,7 @@
// SPDX-License-Identifier: GPL-2.0
#include <linux/bpf.h>
#include <linux/filter.h>
+#include <linux/kmod.h>
#include <linux/netfilter.h>
#include <net/netfilter/nf_bpf_link.h>
@@ -23,8 +24,98 @@ struct bpf_nf_link {
struct nf_hook_ops hook_ops;
struct net *net;
u32 dead;
+ bool defrag;
};
+static int bpf_nf_enable_defrag(struct bpf_nf_link *link)
+{
+ const struct nf_defrag_v4_hook __maybe_unused *v4_hook;
+ const struct nf_defrag_v6_hook __maybe_unused *v6_hook;
+ int err;
+
+ switch (link->hook_ops.pf) {
+#if IS_ENABLED(CONFIG_NF_DEFRAG_IPV4)
+ case NFPROTO_IPV4:
+ rcu_read_lock();
+ v4_hook = rcu_dereference(nf_defrag_v4_hook);
+ if (!v4_hook) {
+ rcu_read_unlock();
+ err = request_module("nf_defrag_ipv4");
+ if (err)
+ return err < 0 ? err : -EINVAL;
+
+ rcu_read_lock();
+ v4_hook = rcu_dereference(nf_defrag_v4_hook);
+ if (!v4_hook) {
+ WARN_ONCE(1, "nf_defrag_ipv4 bad registration");
+ err = -ENOENT;
+ goto out_v4;
+ }
+ }
+
+ err = v4_hook->enable(link->net);
+out_v4:
+ rcu_read_unlock();
+ return err;
+#endif
+#if IS_ENABLED(CONFIG_NF_DEFRAG_IPV6)
+ case NFPROTO_IPV6:
+ rcu_read_lock();
+ v6_hook = rcu_dereference(nf_defrag_v6_hook);
+ if (!v6_hook) {
+ rcu_read_unlock();
+ err = request_module("nf_defrag_ipv6");
+ if (err)
+ return err < 0 ? err : -EINVAL;
+
+ rcu_read_lock();
+ v6_hook = rcu_dereference(nf_defrag_v6_hook);
+ if (!v6_hook) {
+ WARN_ONCE(1, "nf_defrag_ipv6_hooks bad registration");
+ err = -ENOENT;
+ goto out_v6;
+ }
+ }
+
+ err = v6_hook->enable(link->net);
+out_v6:
+ rcu_read_unlock();
+ return err;
+#endif
+ default:
+ return -EAFNOSUPPORT;
+ }
+}
+
+static void bpf_nf_disable_defrag(struct bpf_nf_link *link)
+{
+ const struct nf_defrag_v4_hook __maybe_unused *v4_hook;
+ const struct nf_defrag_v6_hook __maybe_unused *v6_hook;
+
+ switch (link->hook_ops.pf) {
+#if IS_ENABLED(CONFIG_NF_DEFRAG_IPV4)
+ case NFPROTO_IPV4:
+ rcu_read_lock();
+ v4_hook = rcu_dereference(nf_defrag_v4_hook);
+ if (v4_hook)
+ v4_hook->disable(link->net);
+ rcu_read_unlock();
+
+ break;
+#endif
+#if IS_ENABLED(CONFIG_NF_DEFRAG_IPV6)
+ case NFPROTO_IPV6:
+ rcu_read_lock();
+ v6_hook = rcu_dereference(nf_defrag_v6_hook);
+ if (v6_hook)
+ v6_hook->disable(link->net);
+ rcu_read_unlock();
+
+ break;
+ }
+#endif
+}
+
static void bpf_nf_link_release(struct bpf_link *link)
{
struct bpf_nf_link *nf_link = container_of(link, struct bpf_nf_link, link);
@@ -37,6 +128,9 @@ 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);
+
+ if (nf_link->defrag)
+ bpf_nf_disable_defrag(nf_link);
}
static void bpf_nf_link_dealloc(struct bpf_link *link)
@@ -92,6 +186,8 @@ 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 +198,18 @@ 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;
}
@@ -156,6 +251,18 @@ 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;
+ }
+ /* only mark defrag enabled if enabling succeeds so cleanup path
+ * doesn't disable without a corresponding enable
+ */
+ link->defrag = true;
+ }
+
err = nf_register_net_hook(net, &link->hook_ops);
if (err) {
bpf_link_cleanup(&link_primer);
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 600d0caebbd8..c820076c38db 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -1180,6 +1180,11 @@ 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
On Wed, Jul 12, 2023 at 4:44 PM Daniel Xu <[email protected]> wrote:
> +#if IS_ENABLED(CONFIG_NF_DEFRAG_IPV6)
> + case NFPROTO_IPV6:
> + rcu_read_lock();
> + v6_hook = rcu_dereference(nf_defrag_v6_hook);
> + if (!v6_hook) {
> + rcu_read_unlock();
> + err = request_module("nf_defrag_ipv6");
> + if (err)
> + return err < 0 ? err : -EINVAL;
> +
> + rcu_read_lock();
> + v6_hook = rcu_dereference(nf_defrag_v6_hook);
> + if (!v6_hook) {
> + WARN_ONCE(1, "nf_defrag_ipv6_hooks bad registration");
> + err = -ENOENT;
> + goto out_v6;
> + }
> + }
> +
> + err = v6_hook->enable(link->net);
I was about to apply, but luckily caught this issue in my local test:
[ 18.462448] BUG: sleeping function called from invalid context at
kernel/locking/mutex.c:283
[ 18.463238] in_atomic(): 0, irqs_disabled(): 0, non_block: 0, pid:
2042, name: test_progs
[ 18.463927] preempt_count: 0, expected: 0
[ 18.464249] RCU nest depth: 1, expected: 0
[ 18.464631] CPU: 15 PID: 2042 Comm: test_progs Tainted: G
O 6.4.0-04319-g6f6ec4fa00dc #4896
[ 18.465480] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
BIOS rel-1.12.0-59-gc9ba5276e321-prebuilt.qemu.org 04/01/2014
[ 18.466531] Call Trace:
[ 18.466767] <TASK>
[ 18.466975] dump_stack_lvl+0x32/0x40
[ 18.467325] __might_resched+0x129/0x180
[ 18.467691] mutex_lock+0x1a/0x40
[ 18.468057] nf_defrag_ipv4_enable+0x16/0x70
[ 18.468467] bpf_nf_link_attach+0x141/0x300
[ 18.468856] __sys_bpf+0x133e/0x26d0
You cannot call mutex under rcu_read_lock.
Please make sure you have all kernel debug flags on in your testing.
Hi Alexei,
On Wed, Jul 12, 2023 at 05:43:49PM -0700, Alexei Starovoitov wrote:
> On Wed, Jul 12, 2023 at 4:44 PM Daniel Xu <[email protected]> wrote:
> > +#if IS_ENABLED(CONFIG_NF_DEFRAG_IPV6)
> > + case NFPROTO_IPV6:
> > + rcu_read_lock();
> > + v6_hook = rcu_dereference(nf_defrag_v6_hook);
> > + if (!v6_hook) {
> > + rcu_read_unlock();
> > + err = request_module("nf_defrag_ipv6");
> > + if (err)
> > + return err < 0 ? err : -EINVAL;
> > +
> > + rcu_read_lock();
> > + v6_hook = rcu_dereference(nf_defrag_v6_hook);
> > + if (!v6_hook) {
> > + WARN_ONCE(1, "nf_defrag_ipv6_hooks bad registration");
> > + err = -ENOENT;
> > + goto out_v6;
> > + }
> > + }
> > +
> > + err = v6_hook->enable(link->net);
>
> I was about to apply, but luckily caught this issue in my local test:
>
> [ 18.462448] BUG: sleeping function called from invalid context at
> kernel/locking/mutex.c:283
> [ 18.463238] in_atomic(): 0, irqs_disabled(): 0, non_block: 0, pid:
> 2042, name: test_progs
> [ 18.463927] preempt_count: 0, expected: 0
> [ 18.464249] RCU nest depth: 1, expected: 0
> [ 18.464631] CPU: 15 PID: 2042 Comm: test_progs Tainted: G
> O 6.4.0-04319-g6f6ec4fa00dc #4896
> [ 18.465480] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
> BIOS rel-1.12.0-59-gc9ba5276e321-prebuilt.qemu.org 04/01/2014
> [ 18.466531] Call Trace:
> [ 18.466767] <TASK>
> [ 18.466975] dump_stack_lvl+0x32/0x40
> [ 18.467325] __might_resched+0x129/0x180
> [ 18.467691] mutex_lock+0x1a/0x40
> [ 18.468057] nf_defrag_ipv4_enable+0x16/0x70
> [ 18.468467] bpf_nf_link_attach+0x141/0x300
> [ 18.468856] __sys_bpf+0x133e/0x26d0
>
> You cannot call mutex under rcu_read_lock.
Whoops, my bad. I think this patch should fix it:
```
From 7e8927c44452db07ddd7cf0e30bb49215fc044ed Mon Sep 17 00:00:00 2001
Message-ID: <7e8927c44452db07ddd7cf0e30bb49215fc044ed.1689211250.git.dxu@dxuuu.xyz>
From: Daniel Xu <[email protected]>
Date: Wed, 12 Jul 2023 19:17:35 -0600
Subject: [PATCH] netfilter: bpf: Don't hold rcu_read_lock during
enable/disable
->enable()/->disable() takes a mutex which can sleep. You can't sleep
during RCU read side critical section.
Our refcnt on the module will protect us from ->enable()/->disable()
from going away while we call it.
Signed-off-by: Daniel Xu <[email protected]>
---
net/netfilter/nf_bpf_link.c | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)
diff --git a/net/netfilter/nf_bpf_link.c b/net/netfilter/nf_bpf_link.c
index 77ffbf26ba3d..79704cc596aa 100644
--- a/net/netfilter/nf_bpf_link.c
+++ b/net/netfilter/nf_bpf_link.c
@@ -60,9 +60,12 @@ static int bpf_nf_enable_defrag(struct bpf_nf_link *link)
goto out_v4;
}
+ rcu_read_unlock();
err = v4_hook->enable(link->net);
if (err)
module_put(v4_hook->owner);
+
+ return err;
out_v4:
rcu_read_unlock();
return err;
@@ -92,9 +95,12 @@ static int bpf_nf_enable_defrag(struct bpf_nf_link *link)
goto out_v6;
}
+ rcu_read_unlock();
err = v6_hook->enable(link->net);
if (err)
module_put(v6_hook->owner);
+
+ return err;
out_v6:
rcu_read_unlock();
return err;
@@ -114,11 +120,11 @@ static void bpf_nf_disable_defrag(struct bpf_nf_link *link)
case NFPROTO_IPV4:
rcu_read_lock();
v4_hook = rcu_dereference(nf_defrag_v4_hook);
+ rcu_read_unlock();
if (v4_hook) {
v4_hook->disable(link->net);
module_put(v4_hook->owner);
}
- rcu_read_unlock();
break;
#endif
@@ -126,11 +132,11 @@ static void bpf_nf_disable_defrag(struct bpf_nf_link *link)
case NFPROTO_IPV6:
rcu_read_lock();
v6_hook = rcu_dereference(nf_defrag_v6_hook);
+ rcu_read_unlock();
if (v6_hook) {
v6_hook->disable(link->net);
module_put(v6_hook->owner);
}
- rcu_read_unlock();
break;
}
--
2.41.0
```
I'll send out a v5 tomorrow morning unless you feel like applying the
series + this patch today.
>
> Please make sure you have all kernel debug flags on in your testing.
>
Ack. Will make sure lockdep is on.
Thanks,
Daniel
On Wed, Jul 12, 2023 at 6:22 PM Daniel Xu <[email protected]> wrote:
>
> Hi Alexei,
>
> On Wed, Jul 12, 2023 at 05:43:49PM -0700, Alexei Starovoitov wrote:
> > On Wed, Jul 12, 2023 at 4:44 PM Daniel Xu <[email protected]> wrote:
> > > +#if IS_ENABLED(CONFIG_NF_DEFRAG_IPV6)
> > > + case NFPROTO_IPV6:
> > > + rcu_read_lock();
> > > + v6_hook = rcu_dereference(nf_defrag_v6_hook);
> > > + if (!v6_hook) {
> > > + rcu_read_unlock();
> > > + err = request_module("nf_defrag_ipv6");
> > > + if (err)
> > > + return err < 0 ? err : -EINVAL;
> > > +
> > > + rcu_read_lock();
> > > + v6_hook = rcu_dereference(nf_defrag_v6_hook);
> > > + if (!v6_hook) {
> > > + WARN_ONCE(1, "nf_defrag_ipv6_hooks bad registration");
> > > + err = -ENOENT;
> > > + goto out_v6;
> > > + }
> > > + }
> > > +
> > > + err = v6_hook->enable(link->net);
> >
> > I was about to apply, but luckily caught this issue in my local test:
> >
> > [ 18.462448] BUG: sleeping function called from invalid context at
> > kernel/locking/mutex.c:283
> > [ 18.463238] in_atomic(): 0, irqs_disabled(): 0, non_block: 0, pid:
> > 2042, name: test_progs
> > [ 18.463927] preempt_count: 0, expected: 0
> > [ 18.464249] RCU nest depth: 1, expected: 0
> > [ 18.464631] CPU: 15 PID: 2042 Comm: test_progs Tainted: G
> > O 6.4.0-04319-g6f6ec4fa00dc #4896
> > [ 18.465480] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
> > BIOS rel-1.12.0-59-gc9ba5276e321-prebuilt.qemu.org 04/01/2014
> > [ 18.466531] Call Trace:
> > [ 18.466767] <TASK>
> > [ 18.466975] dump_stack_lvl+0x32/0x40
> > [ 18.467325] __might_resched+0x129/0x180
> > [ 18.467691] mutex_lock+0x1a/0x40
> > [ 18.468057] nf_defrag_ipv4_enable+0x16/0x70
> > [ 18.468467] bpf_nf_link_attach+0x141/0x300
> > [ 18.468856] __sys_bpf+0x133e/0x26d0
> >
> > You cannot call mutex under rcu_read_lock.
>
> Whoops, my bad. I think this patch should fix it:
>
> ```
> From 7e8927c44452db07ddd7cf0e30bb49215fc044ed Mon Sep 17 00:00:00 2001
> Message-ID: <7e8927c44452db07ddd7cf0e30bb49215fc044ed.1689211250.git.dxu@dxuuu.xyz>
> From: Daniel Xu <[email protected]>
> Date: Wed, 12 Jul 2023 19:17:35 -0600
> Subject: [PATCH] netfilter: bpf: Don't hold rcu_read_lock during
> enable/disable
>
> ->enable()/->disable() takes a mutex which can sleep. You can't sleep
> during RCU read side critical section.
>
> Our refcnt on the module will protect us from ->enable()/->disable()
> from going away while we call it.
>
> Signed-off-by: Daniel Xu <[email protected]>
> ---
> net/netfilter/nf_bpf_link.c | 10 ++++++++--
> 1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/net/netfilter/nf_bpf_link.c b/net/netfilter/nf_bpf_link.c
> index 77ffbf26ba3d..79704cc596aa 100644
> --- a/net/netfilter/nf_bpf_link.c
> +++ b/net/netfilter/nf_bpf_link.c
> @@ -60,9 +60,12 @@ static int bpf_nf_enable_defrag(struct bpf_nf_link *link)
> goto out_v4;
> }
>
> + rcu_read_unlock();
> err = v4_hook->enable(link->net);
> if (err)
> module_put(v4_hook->owner);
> +
> + return err;
> out_v4:
> rcu_read_unlock();
> return err;
> @@ -92,9 +95,12 @@ static int bpf_nf_enable_defrag(struct bpf_nf_link *link)
> goto out_v6;
> }
>
> + rcu_read_unlock();
> err = v6_hook->enable(link->net);
> if (err)
> module_put(v6_hook->owner);
> +
> + return err;
> out_v6:
> rcu_read_unlock();
> return err;
> @@ -114,11 +120,11 @@ static void bpf_nf_disable_defrag(struct bpf_nf_link *link)
> case NFPROTO_IPV4:
> rcu_read_lock();
> v4_hook = rcu_dereference(nf_defrag_v4_hook);
> + rcu_read_unlock();
> if (v4_hook) {
> v4_hook->disable(link->net);
> module_put(v4_hook->owner);
> }
> - rcu_read_unlock();
>
> break;
> #endif
> @@ -126,11 +132,11 @@ static void bpf_nf_disable_defrag(struct bpf_nf_link *link)
> case NFPROTO_IPV6:
> rcu_read_lock();
> v6_hook = rcu_dereference(nf_defrag_v6_hook);
> + rcu_read_unlock();
No. v6_hook is gone as soon as you unlock it.
On Wed, Jul 12, 2023 at 06:26:13PM -0700, Alexei Starovoitov wrote:
> On Wed, Jul 12, 2023 at 6:22 PM Daniel Xu <[email protected]> wrote:
> >
> > Hi Alexei,
> >
> > On Wed, Jul 12, 2023 at 05:43:49PM -0700, Alexei Starovoitov wrote:
> > > On Wed, Jul 12, 2023 at 4:44 PM Daniel Xu <[email protected]> wrote:
> > > > +#if IS_ENABLED(CONFIG_NF_DEFRAG_IPV6)
> > > > + case NFPROTO_IPV6:
> > > > + rcu_read_lock();
> > > > + v6_hook = rcu_dereference(nf_defrag_v6_hook);
> > > > + if (!v6_hook) {
> > > > + rcu_read_unlock();
> > > > + err = request_module("nf_defrag_ipv6");
> > > > + if (err)
> > > > + return err < 0 ? err : -EINVAL;
> > > > +
> > > > + rcu_read_lock();
> > > > + v6_hook = rcu_dereference(nf_defrag_v6_hook);
> > > > + if (!v6_hook) {
> > > > + WARN_ONCE(1, "nf_defrag_ipv6_hooks bad registration");
> > > > + err = -ENOENT;
> > > > + goto out_v6;
> > > > + }
> > > > + }
> > > > +
> > > > + err = v6_hook->enable(link->net);
> > >
> > > I was about to apply, but luckily caught this issue in my local test:
> > >
> > > [ 18.462448] BUG: sleeping function called from invalid context at
> > > kernel/locking/mutex.c:283
> > > [ 18.463238] in_atomic(): 0, irqs_disabled(): 0, non_block: 0, pid:
> > > 2042, name: test_progs
> > > [ 18.463927] preempt_count: 0, expected: 0
> > > [ 18.464249] RCU nest depth: 1, expected: 0
> > > [ 18.464631] CPU: 15 PID: 2042 Comm: test_progs Tainted: G
> > > O 6.4.0-04319-g6f6ec4fa00dc #4896
> > > [ 18.465480] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
> > > BIOS rel-1.12.0-59-gc9ba5276e321-prebuilt.qemu.org 04/01/2014
> > > [ 18.466531] Call Trace:
> > > [ 18.466767] <TASK>
> > > [ 18.466975] dump_stack_lvl+0x32/0x40
> > > [ 18.467325] __might_resched+0x129/0x180
> > > [ 18.467691] mutex_lock+0x1a/0x40
> > > [ 18.468057] nf_defrag_ipv4_enable+0x16/0x70
> > > [ 18.468467] bpf_nf_link_attach+0x141/0x300
> > > [ 18.468856] __sys_bpf+0x133e/0x26d0
> > >
> > > You cannot call mutex under rcu_read_lock.
> >
> > Whoops, my bad. I think this patch should fix it:
> >
> > ```
> > From 7e8927c44452db07ddd7cf0e30bb49215fc044ed Mon Sep 17 00:00:00 2001
> > Message-ID: <7e8927c44452db07ddd7cf0e30bb49215fc044ed.1689211250.git.dxu@dxuuu.xyz>
> > From: Daniel Xu <[email protected]>
> > Date: Wed, 12 Jul 2023 19:17:35 -0600
> > Subject: [PATCH] netfilter: bpf: Don't hold rcu_read_lock during
> > enable/disable
> >
> > ->enable()/->disable() takes a mutex which can sleep. You can't sleep
> > during RCU read side critical section.
> >
> > Our refcnt on the module will protect us from ->enable()/->disable()
> > from going away while we call it.
> >
> > Signed-off-by: Daniel Xu <[email protected]>
> > ---
> > net/netfilter/nf_bpf_link.c | 10 ++++++++--
> > 1 file changed, 8 insertions(+), 2 deletions(-)
> >
> > diff --git a/net/netfilter/nf_bpf_link.c b/net/netfilter/nf_bpf_link.c
> > index 77ffbf26ba3d..79704cc596aa 100644
> > --- a/net/netfilter/nf_bpf_link.c
> > +++ b/net/netfilter/nf_bpf_link.c
> > @@ -60,9 +60,12 @@ static int bpf_nf_enable_defrag(struct bpf_nf_link *link)
> > goto out_v4;
> > }
> >
> > + rcu_read_unlock();
> > err = v4_hook->enable(link->net);
> > if (err)
> > module_put(v4_hook->owner);
> > +
> > + return err;
> > out_v4:
> > rcu_read_unlock();
> > return err;
> > @@ -92,9 +95,12 @@ static int bpf_nf_enable_defrag(struct bpf_nf_link *link)
> > goto out_v6;
> > }
> >
> > + rcu_read_unlock();
> > err = v6_hook->enable(link->net);
> > if (err)
> > module_put(v6_hook->owner);
> > +
> > + return err;
> > out_v6:
> > rcu_read_unlock();
> > return err;
> > @@ -114,11 +120,11 @@ static void bpf_nf_disable_defrag(struct bpf_nf_link *link)
> > case NFPROTO_IPV4:
> > rcu_read_lock();
> > v4_hook = rcu_dereference(nf_defrag_v4_hook);
> > + rcu_read_unlock();
> > if (v4_hook) {
> > v4_hook->disable(link->net);
> > module_put(v4_hook->owner);
> > }
> > - rcu_read_unlock();
> >
> > break;
> > #endif
> > @@ -126,11 +132,11 @@ static void bpf_nf_disable_defrag(struct bpf_nf_link *link)
> > case NFPROTO_IPV6:
> > rcu_read_lock();
> > v6_hook = rcu_dereference(nf_defrag_v6_hook);
> > + rcu_read_unlock();
>
> No. v6_hook is gone as soon as you unlock it.
I think we're protected here by the try_module_get() on the enable path.
And we only disable defrag if enabling succeeds. The module shouldn't
be able to deregister its hooks until we call the module_put() later.
I think READ_ONCE() would've been more appropriate but I wasn't sure if
that was ok given nf_defrag_v(4|6)_hook is written to by
rcu_assign_pointer() and I was assuming symmetry is necessary.
Does that sound right?
Thanks,
Daniel
On Wed, Jul 12, 2023 at 9:33 PM Daniel Xu <[email protected]> wrote:
>
> On Wed, Jul 12, 2023 at 06:26:13PM -0700, Alexei Starovoitov wrote:
> > On Wed, Jul 12, 2023 at 6:22 PM Daniel Xu <[email protected]> wrote:
> > >
> > > Hi Alexei,
> > >
> > > On Wed, Jul 12, 2023 at 05:43:49PM -0700, Alexei Starovoitov wrote:
> > > > On Wed, Jul 12, 2023 at 4:44 PM Daniel Xu <[email protected]> wrote:
> > > > > +#if IS_ENABLED(CONFIG_NF_DEFRAG_IPV6)
> > > > > + case NFPROTO_IPV6:
> > > > > + rcu_read_lock();
> > > > > + v6_hook = rcu_dereference(nf_defrag_v6_hook);
> > > > > + if (!v6_hook) {
> > > > > + rcu_read_unlock();
> > > > > + err = request_module("nf_defrag_ipv6");
> > > > > + if (err)
> > > > > + return err < 0 ? err : -EINVAL;
> > > > > +
> > > > > + rcu_read_lock();
> > > > > + v6_hook = rcu_dereference(nf_defrag_v6_hook);
> > > > > + if (!v6_hook) {
> > > > > + WARN_ONCE(1, "nf_defrag_ipv6_hooks bad registration");
> > > > > + err = -ENOENT;
> > > > > + goto out_v6;
> > > > > + }
> > > > > + }
> > > > > +
> > > > > + err = v6_hook->enable(link->net);
> > > >
> > > > I was about to apply, but luckily caught this issue in my local test:
> > > >
> > > > [ 18.462448] BUG: sleeping function called from invalid context at
> > > > kernel/locking/mutex.c:283
> > > > [ 18.463238] in_atomic(): 0, irqs_disabled(): 0, non_block: 0, pid:
> > > > 2042, name: test_progs
> > > > [ 18.463927] preempt_count: 0, expected: 0
> > > > [ 18.464249] RCU nest depth: 1, expected: 0
> > > > [ 18.464631] CPU: 15 PID: 2042 Comm: test_progs Tainted: G
> > > > O 6.4.0-04319-g6f6ec4fa00dc #4896
> > > > [ 18.465480] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
> > > > BIOS rel-1.12.0-59-gc9ba5276e321-prebuilt.qemu.org 04/01/2014
> > > > [ 18.466531] Call Trace:
> > > > [ 18.466767] <TASK>
> > > > [ 18.466975] dump_stack_lvl+0x32/0x40
> > > > [ 18.467325] __might_resched+0x129/0x180
> > > > [ 18.467691] mutex_lock+0x1a/0x40
> > > > [ 18.468057] nf_defrag_ipv4_enable+0x16/0x70
> > > > [ 18.468467] bpf_nf_link_attach+0x141/0x300
> > > > [ 18.468856] __sys_bpf+0x133e/0x26d0
> > > >
> > > > You cannot call mutex under rcu_read_lock.
> > >
> > > Whoops, my bad. I think this patch should fix it:
> > >
> > > ```
> > > From 7e8927c44452db07ddd7cf0e30bb49215fc044ed Mon Sep 17 00:00:00 2001
> > > Message-ID: <7e8927c44452db07ddd7cf0e30bb49215fc044ed.1689211250.git.dxu@dxuuu.xyz>
> > > From: Daniel Xu <[email protected]>
> > > Date: Wed, 12 Jul 2023 19:17:35 -0600
> > > Subject: [PATCH] netfilter: bpf: Don't hold rcu_read_lock during
> > > enable/disable
> > >
> > > ->enable()/->disable() takes a mutex which can sleep. You can't sleep
> > > during RCU read side critical section.
> > >
> > > Our refcnt on the module will protect us from ->enable()/->disable()
> > > from going away while we call it.
> > >
> > > Signed-off-by: Daniel Xu <[email protected]>
> > > ---
> > > net/netfilter/nf_bpf_link.c | 10 ++++++++--
> > > 1 file changed, 8 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/net/netfilter/nf_bpf_link.c b/net/netfilter/nf_bpf_link.c
> > > index 77ffbf26ba3d..79704cc596aa 100644
> > > --- a/net/netfilter/nf_bpf_link.c
> > > +++ b/net/netfilter/nf_bpf_link.c
> > > @@ -60,9 +60,12 @@ static int bpf_nf_enable_defrag(struct bpf_nf_link *link)
> > > goto out_v4;
> > > }
> > >
> > > + rcu_read_unlock();
> > > err = v4_hook->enable(link->net);
> > > if (err)
> > > module_put(v4_hook->owner);
> > > +
> > > + return err;
> > > out_v4:
> > > rcu_read_unlock();
> > > return err;
> > > @@ -92,9 +95,12 @@ static int bpf_nf_enable_defrag(struct bpf_nf_link *link)
> > > goto out_v6;
> > > }
> > >
> > > + rcu_read_unlock();
> > > err = v6_hook->enable(link->net);
> > > if (err)
> > > module_put(v6_hook->owner);
> > > +
> > > + return err;
> > > out_v6:
> > > rcu_read_unlock();
> > > return err;
> > > @@ -114,11 +120,11 @@ static void bpf_nf_disable_defrag(struct bpf_nf_link *link)
> > > case NFPROTO_IPV4:
> > > rcu_read_lock();
> > > v4_hook = rcu_dereference(nf_defrag_v4_hook);
> > > + rcu_read_unlock();
> > > if (v4_hook) {
> > > v4_hook->disable(link->net);
> > > module_put(v4_hook->owner);
> > > }
> > > - rcu_read_unlock();
> > >
> > > break;
> > > #endif
> > > @@ -126,11 +132,11 @@ static void bpf_nf_disable_defrag(struct bpf_nf_link *link)
> > > case NFPROTO_IPV6:
> > > rcu_read_lock();
> > > v6_hook = rcu_dereference(nf_defrag_v6_hook);
> > > + rcu_read_unlock();
> >
> > No. v6_hook is gone as soon as you unlock it.
>
> I think we're protected here by the try_module_get() on the enable path.
> And we only disable defrag if enabling succeeds. The module shouldn't
> be able to deregister its hooks until we call the module_put() later.
>
> I think READ_ONCE() would've been more appropriate but I wasn't sure if
> that was ok given nf_defrag_v(4|6)_hook is written to by
> rcu_assign_pointer() and I was assuming symmetry is necessary.
Why is rcu_assign_pointer() used?
If it's not RCU protected, what is the point of rcu_*() accessors
and rcu_read_lock() ?
In general, the pattern:
rcu_read_lock();
ptr = rcu_dereference(...);
rcu_read_unlock();
ptr->..
is a bug. 100%.
On Thu, Jul 13, 2023 at 04:10:03PM -0700, Alexei Starovoitov wrote:
> On Wed, Jul 12, 2023 at 9:33 PM Daniel Xu <[email protected]> wrote:
> >
> > On Wed, Jul 12, 2023 at 06:26:13PM -0700, Alexei Starovoitov wrote:
> > > On Wed, Jul 12, 2023 at 6:22 PM Daniel Xu <[email protected]> wrote:
> > > >
> > > > Hi Alexei,
> > > >
> > > > On Wed, Jul 12, 2023 at 05:43:49PM -0700, Alexei Starovoitov wrote:
> > > > > On Wed, Jul 12, 2023 at 4:44 PM Daniel Xu <[email protected]> wrote:
> > > > > > +#if IS_ENABLED(CONFIG_NF_DEFRAG_IPV6)
> > > > > > + case NFPROTO_IPV6:
> > > > > > + rcu_read_lock();
> > > > > > + v6_hook = rcu_dereference(nf_defrag_v6_hook);
> > > > > > + if (!v6_hook) {
> > > > > > + rcu_read_unlock();
> > > > > > + err = request_module("nf_defrag_ipv6");
> > > > > > + if (err)
> > > > > > + return err < 0 ? err : -EINVAL;
> > > > > > +
> > > > > > + rcu_read_lock();
> > > > > > + v6_hook = rcu_dereference(nf_defrag_v6_hook);
> > > > > > + if (!v6_hook) {
> > > > > > + WARN_ONCE(1, "nf_defrag_ipv6_hooks bad registration");
> > > > > > + err = -ENOENT;
> > > > > > + goto out_v6;
> > > > > > + }
> > > > > > + }
> > > > > > +
> > > > > > + err = v6_hook->enable(link->net);
> > > > >
> > > > > I was about to apply, but luckily caught this issue in my local test:
> > > > >
> > > > > [ 18.462448] BUG: sleeping function called from invalid context at
> > > > > kernel/locking/mutex.c:283
> > > > > [ 18.463238] in_atomic(): 0, irqs_disabled(): 0, non_block: 0, pid:
> > > > > 2042, name: test_progs
> > > > > [ 18.463927] preempt_count: 0, expected: 0
> > > > > [ 18.464249] RCU nest depth: 1, expected: 0
> > > > > [ 18.464631] CPU: 15 PID: 2042 Comm: test_progs Tainted: G
> > > > > O 6.4.0-04319-g6f6ec4fa00dc #4896
> > > > > [ 18.465480] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
> > > > > BIOS rel-1.12.0-59-gc9ba5276e321-prebuilt.qemu.org 04/01/2014
> > > > > [ 18.466531] Call Trace:
> > > > > [ 18.466767] <TASK>
> > > > > [ 18.466975] dump_stack_lvl+0x32/0x40
> > > > > [ 18.467325] __might_resched+0x129/0x180
> > > > > [ 18.467691] mutex_lock+0x1a/0x40
> > > > > [ 18.468057] nf_defrag_ipv4_enable+0x16/0x70
> > > > > [ 18.468467] bpf_nf_link_attach+0x141/0x300
> > > > > [ 18.468856] __sys_bpf+0x133e/0x26d0
> > > > >
> > > > > You cannot call mutex under rcu_read_lock.
> > > >
> > > > Whoops, my bad. I think this patch should fix it:
> > > >
> > > > ```
> > > > From 7e8927c44452db07ddd7cf0e30bb49215fc044ed Mon Sep 17 00:00:00 2001
> > > > Message-ID: <7e8927c44452db07ddd7cf0e30bb49215fc044ed.1689211250.git.dxu@dxuuu.xyz>
> > > > From: Daniel Xu <[email protected]>
> > > > Date: Wed, 12 Jul 2023 19:17:35 -0600
> > > > Subject: [PATCH] netfilter: bpf: Don't hold rcu_read_lock during
> > > > enable/disable
> > > >
> > > > ->enable()/->disable() takes a mutex which can sleep. You can't sleep
> > > > during RCU read side critical section.
> > > >
> > > > Our refcnt on the module will protect us from ->enable()/->disable()
> > > > from going away while we call it.
> > > >
> > > > Signed-off-by: Daniel Xu <[email protected]>
> > > > ---
> > > > net/netfilter/nf_bpf_link.c | 10 ++++++++--
> > > > 1 file changed, 8 insertions(+), 2 deletions(-)
> > > >
> > > > diff --git a/net/netfilter/nf_bpf_link.c b/net/netfilter/nf_bpf_link.c
> > > > index 77ffbf26ba3d..79704cc596aa 100644
> > > > --- a/net/netfilter/nf_bpf_link.c
> > > > +++ b/net/netfilter/nf_bpf_link.c
> > > > @@ -60,9 +60,12 @@ static int bpf_nf_enable_defrag(struct bpf_nf_link *link)
> > > > goto out_v4;
> > > > }
> > > >
> > > > + rcu_read_unlock();
> > > > err = v4_hook->enable(link->net);
> > > > if (err)
> > > > module_put(v4_hook->owner);
> > > > +
> > > > + return err;
> > > > out_v4:
> > > > rcu_read_unlock();
> > > > return err;
> > > > @@ -92,9 +95,12 @@ static int bpf_nf_enable_defrag(struct bpf_nf_link *link)
> > > > goto out_v6;
> > > > }
> > > >
> > > > + rcu_read_unlock();
> > > > err = v6_hook->enable(link->net);
> > > > if (err)
> > > > module_put(v6_hook->owner);
> > > > +
> > > > + return err;
> > > > out_v6:
> > > > rcu_read_unlock();
> > > > return err;
> > > > @@ -114,11 +120,11 @@ static void bpf_nf_disable_defrag(struct bpf_nf_link *link)
> > > > case NFPROTO_IPV4:
> > > > rcu_read_lock();
> > > > v4_hook = rcu_dereference(nf_defrag_v4_hook);
> > > > + rcu_read_unlock();
> > > > if (v4_hook) {
> > > > v4_hook->disable(link->net);
> > > > module_put(v4_hook->owner);
> > > > }
> > > > - rcu_read_unlock();
> > > >
> > > > break;
> > > > #endif
> > > > @@ -126,11 +132,11 @@ static void bpf_nf_disable_defrag(struct bpf_nf_link *link)
> > > > case NFPROTO_IPV6:
> > > > rcu_read_lock();
> > > > v6_hook = rcu_dereference(nf_defrag_v6_hook);
> > > > + rcu_read_unlock();
> > >
> > > No. v6_hook is gone as soon as you unlock it.
> >
> > I think we're protected here by the try_module_get() on the enable path.
> > And we only disable defrag if enabling succeeds. The module shouldn't
> > be able to deregister its hooks until we call the module_put() later.
> >
> > I think READ_ONCE() would've been more appropriate but I wasn't sure if
> > that was ok given nf_defrag_v(4|6)_hook is written to by
> > rcu_assign_pointer() and I was assuming symmetry is necessary.
>
> Why is rcu_assign_pointer() used?
> If it's not RCU protected, what is the point of rcu_*() accessors
> and rcu_read_lock() ?
>
> In general, the pattern:
> rcu_read_lock();
> ptr = rcu_dereference(...);
> rcu_read_unlock();
> ptr->..
> is a bug. 100%.
>
The reason I left it like this is b/c otherwise I think there is a race
with module unload and taking a refcnt. For example:
ptr = READ_ONCE(global_var)
<module unload on other cpu>
// ptr invalid
try_module_get(ptr->owner)
I think the the synchronize_rcu() call in
kernel/module/main.c:free_module() protects against that race based on
my reading.
Maybe the ->enable() path can store a copy of the hook ptr in
struct bpf_nf_link to get rid of the odd rcu_dereference()?
Open to other ideas too -- would appreciate any hints.
Thanks,
Daniel
Daniel Xu <[email protected]> wrote:
> On Thu, Jul 13, 2023 at 04:10:03PM -0700, Alexei Starovoitov wrote:
> > Why is rcu_assign_pointer() used?
> > If it's not RCU protected, what is the point of rcu_*() accessors
> > and rcu_read_lock() ?
> >
> > In general, the pattern:
> > rcu_read_lock();
> > ptr = rcu_dereference(...);
> > rcu_read_unlock();
> > ptr->..
> > is a bug. 100%.
FWIW, I agree with Alexei, it does look... dodgy.
> The reason I left it like this is b/c otherwise I think there is a race
> with module unload and taking a refcnt. For example:
>
> ptr = READ_ONCE(global_var)
> <module unload on other cpu>
> // ptr invalid
> try_module_get(ptr->owner)
>
Yes, I agree.
> I think the the synchronize_rcu() call in
> kernel/module/main.c:free_module() protects against that race based on
> my reading.
>
> Maybe the ->enable() path can store a copy of the hook ptr in
> struct bpf_nf_link to get rid of the odd rcu_dereference()?
>
> Open to other ideas too -- would appreciate any hints.
I would suggest the following:
- Switch ordering of patches 2 and 3.
What is currently patch 3 would add the .owner fields only.
Then, what is currently patch #2 would document the rcu/modref
interaction like this (omitting error checking for brevity):
rcu_read_lock();
v6_hook = rcu_dereference(nf_defrag_v6_hook);
if (!v6_hook) {
rcu_read_unlock();
err = request_module("nf_defrag_ipv6");
if (err)
return err < 0 ? err : -EINVAL;
rcu_read_lock();
v6_hook = rcu_dereference(nf_defrag_v6_hook);
}
if (v6_hook && try_module_get(v6_hook->owner))
v6_hook = rcu_pointer_handoff(v6_hook);
else
v6_hook = NULL;
rcu_read_unlock();
if (!v6_hook)
err();
v6_hook->enable();
I'd store the v4/6_hook pointer in the nf bpf link struct, its probably more
self-explanatory for the disable side in that we did pick up a module reference
that we still own at delete time, without need for any rcu involvement.
Because above handoff is repetitive for ipv4 and ipv6,
I suggest to add an agnostic helper for this.
I know you added distinct structures for ipv4 and ipv6 but if they would use
the same one you could add
static const struct nf_defrag_hook *get_proto_frag_hook(const struct nf_defrag_hook __rcu *hook,
const char *modulename);
And then use it like:
v4_hook = get_proto_frag_hook(nf_defrag_v4_hook, "nf_defrag_ipv4");
Without a need to copy the modprobe and handoff part.
What do you think?
Hi Florian,
On Fri, Jul 14, 2023 at 11:47:41AM +0200, Florian Westphal wrote:
> Daniel Xu <[email protected]> wrote:
> > On Thu, Jul 13, 2023 at 04:10:03PM -0700, Alexei Starovoitov wrote:
> > > Why is rcu_assign_pointer() used?
> > > If it's not RCU protected, what is the point of rcu_*() accessors
> > > and rcu_read_lock() ?
> > >
> > > In general, the pattern:
> > > rcu_read_lock();
> > > ptr = rcu_dereference(...);
> > > rcu_read_unlock();
> > > ptr->..
> > > is a bug. 100%.
>
> FWIW, I agree with Alexei, it does look... dodgy.
>
> > The reason I left it like this is b/c otherwise I think there is a race
> > with module unload and taking a refcnt. For example:
> >
> > ptr = READ_ONCE(global_var)
> > <module unload on other cpu>
> > // ptr invalid
> > try_module_get(ptr->owner)
> >
>
> Yes, I agree.
>
> > I think the the synchronize_rcu() call in
> > kernel/module/main.c:free_module() protects against that race based on
> > my reading.
> >
> > Maybe the ->enable() path can store a copy of the hook ptr in
> > struct bpf_nf_link to get rid of the odd rcu_dereference()?
> >
> > Open to other ideas too -- would appreciate any hints.
>
> I would suggest the following:
>
> - Switch ordering of patches 2 and 3.
> What is currently patch 3 would add the .owner fields only.
>
> Then, what is currently patch #2 would document the rcu/modref
> interaction like this (omitting error checking for brevity):
>
> rcu_read_lock();
> v6_hook = rcu_dereference(nf_defrag_v6_hook);
> if (!v6_hook) {
> rcu_read_unlock();
> err = request_module("nf_defrag_ipv6");
> if (err)
> return err < 0 ? err : -EINVAL;
> rcu_read_lock();
> v6_hook = rcu_dereference(nf_defrag_v6_hook);
> }
>
> if (v6_hook && try_module_get(v6_hook->owner))
> v6_hook = rcu_pointer_handoff(v6_hook);
> else
> v6_hook = NULL;
>
> rcu_read_unlock();
>
> if (!v6_hook)
> err();
> v6_hook->enable();
>
>
> I'd store the v4/6_hook pointer in the nf bpf link struct, its probably more
> self-explanatory for the disable side in that we did pick up a module reference
> that we still own at delete time, without need for any rcu involvement.
>
> Because above handoff is repetitive for ipv4 and ipv6,
> I suggest to add an agnostic helper for this.
>
> I know you added distinct structures for ipv4 and ipv6 but if they would use
> the same one you could add
>
> static const struct nf_defrag_hook *get_proto_frag_hook(const struct nf_defrag_hook __rcu *hook,
> const char *modulename);
>
> And then use it like:
>
> v4_hook = get_proto_frag_hook(nf_defrag_v4_hook, "nf_defrag_ipv4");
>
> Without a need to copy the modprobe and handoff part.
>
> What do you think?
That sounds reasonable to me. I'll give it a shot. Thanks for the input!
Daniel