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Merge branch 'bpf-multi-prog-prep'
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Jakub Sitnicki says:

====================
This patch set prepares ground for link-based multi-prog attachment for
future netns attach types, with BPF_SK_LOOKUP attach type in mind [0].

Two changes are needed in order to attach and run a series of BPF programs:

  1) an bpf_prog_array of programs to run (patch #2), and
  2) a list of attached links to keep track of attachments (patch #3).

Nothing changes for BPF flow_dissector. Just as before only one program can
be attached to netns.

In v3 I've simplified patch #2 that introduces bpf_prog_array to take
advantage of the fact that it will hold at most one program for now.

In particular, I'm no longer using bpf_prog_array_copy. It turned out to be
less suitable for link operations than I thought as it fails to append the
same BPF program.

bpf_prog_array_replace_item is also gone, because we know we always want to
replace the first element in prog_array.

Naturally the code that handles bpf_prog_array will need change once
more when there is a program type that allows multi-prog attachment. But I
feel it will be better to do it gradually and present it together with
tests that actually exercise multi-prog code paths.

[0] https://lore.kernel.org/bpf/[email protected]/

v2 -> v3:
- Don't check if run_array is null in link update callback. (Martin)
- Allow updating the link with the same BPF program. (Andrii)
- Add patch #4 with a test for the above case.
- Kill bpf_prog_array_replace_item. Access the run_array directly.
- Switch from bpf_prog_array_copy() to bpf_prog_array_alloc(1, ...).
- Replace rcu_deref_protected & RCU_INIT_POINTER with rcu_replace_pointer.
- Drop Andrii's Ack from patch #2. Code changed.

v1 -> v2:

- Show with a (void) cast that bpf_prog_array_replace_item() return value
  is ignored on purpose. (Andrii)
- Explain why bpf-cgroup cannot replace programs in bpf_prog_array based
  on bpf_prog pointer comparison in patch #2 description. (Andrii)
====================

Signed-off-by: Alexei Starovoitov <[email protected]>
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Alexei Starovoitov committed Jun 30, 2020
2 parents 517bbe1 + 6ebb85c commit 951f38c
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Showing 5 changed files with 160 additions and 76 deletions.
3 changes: 2 additions & 1 deletion include/net/flow_dissector.h
Original file line number Diff line number Diff line change
Expand Up @@ -372,7 +372,8 @@ flow_dissector_init_keys(struct flow_dissector_key_control *key_control,
}

#ifdef CONFIG_BPF_SYSCALL
int flow_dissector_bpf_prog_attach(struct net *net, struct bpf_prog *prog);
int flow_dissector_bpf_prog_attach_check(struct net *net,
struct bpf_prog *prog);
#endif /* CONFIG_BPF_SYSCALL */

#endif
7 changes: 5 additions & 2 deletions include/net/netns/bpf.h
Original file line number Diff line number Diff line change
Expand Up @@ -9,10 +9,13 @@
#include <linux/bpf-netns.h>

struct bpf_prog;
struct bpf_prog_array;

struct netns_bpf {
struct bpf_prog __rcu *progs[MAX_NETNS_BPF_ATTACH_TYPE];
struct bpf_link *links[MAX_NETNS_BPF_ATTACH_TYPE];
/* Array of programs to run compiled from progs or links */
struct bpf_prog_array __rcu *run_array[MAX_NETNS_BPF_ATTACH_TYPE];
struct bpf_prog *progs[MAX_NETNS_BPF_ATTACH_TYPE];
struct list_head links[MAX_NETNS_BPF_ATTACH_TYPE];
};

#endif /* __NETNS_BPF_H__ */
162 changes: 113 additions & 49 deletions kernel/bpf/net_namespace.c
Original file line number Diff line number Diff line change
Expand Up @@ -19,18 +19,21 @@ struct bpf_netns_link {
* with netns_bpf_mutex held.
*/
struct net *net;
struct list_head node; /* node in list of links attached to net */
};

/* Protects updates to netns_bpf */
DEFINE_MUTEX(netns_bpf_mutex);

/* Must be called with netns_bpf_mutex held. */
static void __net_exit bpf_netns_link_auto_detach(struct bpf_link *link)
static void netns_bpf_run_array_detach(struct net *net,
enum netns_bpf_attach_type type)
{
struct bpf_netns_link *net_link =
container_of(link, struct bpf_netns_link, link);
struct bpf_prog_array *run_array;

net_link->net = NULL;
run_array = rcu_replace_pointer(net->bpf.run_array[type], NULL,
lockdep_is_held(&netns_bpf_mutex));
bpf_prog_array_free(run_array);
}

static void bpf_netns_link_release(struct bpf_link *link)
Expand All @@ -54,8 +57,8 @@ static void bpf_netns_link_release(struct bpf_link *link)
if (!net)
goto out_unlock;

net->bpf.links[type] = NULL;
RCU_INIT_POINTER(net->bpf.progs[type], NULL);
netns_bpf_run_array_detach(net, type);
list_del(&net_link->node);

out_unlock:
mutex_unlock(&netns_bpf_mutex);
Expand All @@ -76,6 +79,7 @@ static int bpf_netns_link_update_prog(struct bpf_link *link,
struct bpf_netns_link *net_link =
container_of(link, struct bpf_netns_link, link);
enum netns_bpf_attach_type type = net_link->netns_type;
struct bpf_prog_array *run_array;
struct net *net;
int ret = 0;

Expand All @@ -93,8 +97,11 @@ static int bpf_netns_link_update_prog(struct bpf_link *link,
goto out_unlock;
}

run_array = rcu_dereference_protected(net->bpf.run_array[type],
lockdep_is_held(&netns_bpf_mutex));
WRITE_ONCE(run_array->items[0].prog, new_prog);

old_prog = xchg(&link->prog, new_prog);
rcu_assign_pointer(net->bpf.progs[type], new_prog);
bpf_prog_put(old_prog);

out_unlock:
Expand Down Expand Up @@ -142,14 +149,38 @@ static const struct bpf_link_ops bpf_netns_link_ops = {
.show_fdinfo = bpf_netns_link_show_fdinfo,
};

/* Must be called with netns_bpf_mutex held. */
static int __netns_bpf_prog_query(const union bpf_attr *attr,
union bpf_attr __user *uattr,
struct net *net,
enum netns_bpf_attach_type type)
{
__u32 __user *prog_ids = u64_to_user_ptr(attr->query.prog_ids);
struct bpf_prog_array *run_array;
u32 prog_cnt = 0, flags = 0;

run_array = rcu_dereference_protected(net->bpf.run_array[type],
lockdep_is_held(&netns_bpf_mutex));
if (run_array)
prog_cnt = bpf_prog_array_length(run_array);

if (copy_to_user(&uattr->query.attach_flags, &flags, sizeof(flags)))
return -EFAULT;
if (copy_to_user(&uattr->query.prog_cnt, &prog_cnt, sizeof(prog_cnt)))
return -EFAULT;
if (!attr->query.prog_cnt || !prog_ids || !prog_cnt)
return 0;

return bpf_prog_array_copy_to_user(run_array, prog_ids,
attr->query.prog_cnt);
}

int netns_bpf_prog_query(const union bpf_attr *attr,
union bpf_attr __user *uattr)
{
__u32 __user *prog_ids = u64_to_user_ptr(attr->query.prog_ids);
u32 prog_id, prog_cnt = 0, flags = 0;
enum netns_bpf_attach_type type;
struct bpf_prog *attached;
struct net *net;
int ret;

if (attr->query.query_flags)
return -EINVAL;
Expand All @@ -162,33 +193,19 @@ int netns_bpf_prog_query(const union bpf_attr *attr,
if (IS_ERR(net))
return PTR_ERR(net);

rcu_read_lock();
attached = rcu_dereference(net->bpf.progs[type]);
if (attached) {
prog_cnt = 1;
prog_id = attached->aux->id;
}
rcu_read_unlock();
mutex_lock(&netns_bpf_mutex);
ret = __netns_bpf_prog_query(attr, uattr, net, type);
mutex_unlock(&netns_bpf_mutex);

put_net(net);

if (copy_to_user(&uattr->query.attach_flags, &flags, sizeof(flags)))
return -EFAULT;
if (copy_to_user(&uattr->query.prog_cnt, &prog_cnt, sizeof(prog_cnt)))
return -EFAULT;

if (!attr->query.prog_cnt || !prog_ids || !prog_cnt)
return 0;

if (copy_to_user(prog_ids, &prog_id, sizeof(u32)))
return -EFAULT;

return 0;
return ret;
}

int netns_bpf_prog_attach(const union bpf_attr *attr, struct bpf_prog *prog)
{
struct bpf_prog_array *run_array;
enum netns_bpf_attach_type type;
struct bpf_prog *attached;
struct net *net;
int ret;

Expand All @@ -200,19 +217,47 @@ int netns_bpf_prog_attach(const union bpf_attr *attr, struct bpf_prog *prog)
mutex_lock(&netns_bpf_mutex);

/* Attaching prog directly is not compatible with links */
if (net->bpf.links[type]) {
if (!list_empty(&net->bpf.links[type])) {
ret = -EEXIST;
goto out_unlock;
}

switch (type) {
case NETNS_BPF_FLOW_DISSECTOR:
ret = flow_dissector_bpf_prog_attach(net, prog);
ret = flow_dissector_bpf_prog_attach_check(net, prog);
break;
default:
ret = -EINVAL;
break;
}
if (ret)
goto out_unlock;

attached = net->bpf.progs[type];
if (attached == prog) {
/* The same program cannot be attached twice */
ret = -EINVAL;
goto out_unlock;
}

run_array = rcu_dereference_protected(net->bpf.run_array[type],
lockdep_is_held(&netns_bpf_mutex));
if (run_array) {
WRITE_ONCE(run_array->items[0].prog, prog);
} else {
run_array = bpf_prog_array_alloc(1, GFP_KERNEL);
if (!run_array) {
ret = -ENOMEM;
goto out_unlock;
}
run_array->items[0].prog = prog;
rcu_assign_pointer(net->bpf.run_array[type], run_array);
}

net->bpf.progs[type] = prog;
if (attached)
bpf_prog_put(attached);

out_unlock:
mutex_unlock(&netns_bpf_mutex);

Expand All @@ -226,14 +271,14 @@ static int __netns_bpf_prog_detach(struct net *net,
struct bpf_prog *attached;

/* Progs attached via links cannot be detached */
if (net->bpf.links[type])
if (!list_empty(&net->bpf.links[type]))
return -EINVAL;

attached = rcu_dereference_protected(net->bpf.progs[type],
lockdep_is_held(&netns_bpf_mutex));
attached = net->bpf.progs[type];
if (!attached)
return -ENOENT;
RCU_INIT_POINTER(net->bpf.progs[type], NULL);
netns_bpf_run_array_detach(net, type);
net->bpf.progs[type] = NULL;
bpf_prog_put(attached);
return 0;
}
Expand All @@ -257,27 +302,27 @@ int netns_bpf_prog_detach(const union bpf_attr *attr)
static int netns_bpf_link_attach(struct net *net, struct bpf_link *link,
enum netns_bpf_attach_type type)
{
struct bpf_prog *prog;
struct bpf_netns_link *net_link =
container_of(link, struct bpf_netns_link, link);
struct bpf_prog_array *run_array;
int err;

mutex_lock(&netns_bpf_mutex);

/* Allow attaching only one prog or link for now */
if (net->bpf.links[type]) {
if (!list_empty(&net->bpf.links[type])) {
err = -E2BIG;
goto out_unlock;
}
/* Links are not compatible with attaching prog directly */
prog = rcu_dereference_protected(net->bpf.progs[type],
lockdep_is_held(&netns_bpf_mutex));
if (prog) {
if (net->bpf.progs[type]) {
err = -EEXIST;
goto out_unlock;
}

switch (type) {
case NETNS_BPF_FLOW_DISSECTOR:
err = flow_dissector_bpf_prog_attach(net, link->prog);
err = flow_dissector_bpf_prog_attach_check(net, link->prog);
break;
default:
err = -EINVAL;
Expand All @@ -286,7 +331,15 @@ static int netns_bpf_link_attach(struct net *net, struct bpf_link *link,
if (err)
goto out_unlock;

net->bpf.links[type] = link;
run_array = bpf_prog_array_alloc(1, GFP_KERNEL);
if (!run_array) {
err = -ENOMEM;
goto out_unlock;
}
run_array->items[0].prog = link->prog;
rcu_assign_pointer(net->bpf.run_array[type], run_array);

list_add_tail(&net_link->node, &net->bpf.links[type]);

out_unlock:
mutex_unlock(&netns_bpf_mutex);
Expand Down Expand Up @@ -345,23 +398,34 @@ int netns_bpf_link_create(const union bpf_attr *attr, struct bpf_prog *prog)
return err;
}

static int __net_init netns_bpf_pernet_init(struct net *net)
{
int type;

for (type = 0; type < MAX_NETNS_BPF_ATTACH_TYPE; type++)
INIT_LIST_HEAD(&net->bpf.links[type]);

return 0;
}

static void __net_exit netns_bpf_pernet_pre_exit(struct net *net)
{
enum netns_bpf_attach_type type;
struct bpf_link *link;
struct bpf_netns_link *net_link;

mutex_lock(&netns_bpf_mutex);
for (type = 0; type < MAX_NETNS_BPF_ATTACH_TYPE; type++) {
link = net->bpf.links[type];
if (link)
bpf_netns_link_auto_detach(link);
else
__netns_bpf_prog_detach(net, type);
netns_bpf_run_array_detach(net, type);
list_for_each_entry(net_link, &net->bpf.links[type], node)
net_link->net = NULL; /* auto-detach link */
if (net->bpf.progs[type])
bpf_prog_put(net->bpf.progs[type]);
}
mutex_unlock(&netns_bpf_mutex);
}

static struct pernet_operations netns_bpf_pernet_ops __net_initdata = {
.init = netns_bpf_pernet_init,
.pre_exit = netns_bpf_pernet_pre_exit,
};

Expand Down
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