Prepare for having multi-prog attachments for new netns attach types by
storing programs to run in a bpf_prog_array, which is well suited for
iterating over programs and running them in sequence.
Because bpf_prog_array is dynamically resized, after this change a
potentially blocking memory allocation in bpf(PROG_QUERY) callback can
happen, in order to collect program IDs before copying the values to
user-space supplied buffer. This forces us to adapt how we protect access
to the attached program in the callback. As bpf_prog_array_copy_to_user()
helper can sleep, we switch from an RCU read lock to holding a mutex that
serializes updaters.
To handle bpf(PROG_ATTACH) scenario when we are replacing an already
attached program, we introduce a new bpf_prog_array helper called
bpf_prog_array_replace_item that will exchange the old program with a new
one. bpf-cgroup does away with such helper by computing an index into the
array from a program position in an external list of attached
programs/links. Such approach fails when a dummy prog is left in the array
after a memory allocation failure on link release, but is necessary in
bpf-cgroup case because the same BPF program can be present in the array
multiple times due to inheritance, and attachment cannot be reliably
identified by bpf_prog pointer comparison.
No functional changes intended.
Acked-by: Andrii Nakryiko <andr...@fb.com>
Signed-off-by: Jakub Sitnicki <ja...@cloudflare.com>
---
include/linux/bpf.h | 3 +
include/net/netns/bpf.h | 5 +-
kernel/bpf/core.c | 20 ++++--
kernel/bpf/net_namespace.c | 137 +++++++++++++++++++++++++++----------
net/core/flow_dissector.c | 21 +++---
5 files changed, 132 insertions(+), 54 deletions(-)
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 1e1501ee53ce..5d0506f46f24 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -928,6 +928,9 @@ int bpf_prog_array_copy(struct bpf_prog_array *old_array,
struct bpf_prog *exclude_prog,
struct bpf_prog *include_prog,
struct bpf_prog_array **new_array);
+int bpf_prog_array_replace_item(struct bpf_prog_array *array,
+ struct bpf_prog *old_prog,
+ struct bpf_prog *new_prog);
#define __BPF_PROG_RUN_ARRAY(array, ctx, func, check_non_null) \
({ \
diff --git a/include/net/netns/bpf.h b/include/net/netns/bpf.h
index a8dce2a380c8..a5015bda9979 100644
--- a/include/net/netns/bpf.h
+++ b/include/net/netns/bpf.h
@@ -9,9 +9,12 @@
#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];
+ /* 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 bpf_link *links[MAX_NETNS_BPF_ATTACH_TYPE];
};
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 9df4cc9a2907..07937ddf722f 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -1946,16 +1946,26 @@ int bpf_prog_array_copy_to_user(struct bpf_prog_array
*array,
return 0;
}
-void bpf_prog_array_delete_safe(struct bpf_prog_array *array,
- struct bpf_prog *old_prog)
+int bpf_prog_array_replace_item(struct bpf_prog_array *array,
+ struct bpf_prog *old_prog,
+ struct bpf_prog *new_prog)
{
struct bpf_prog_array_item *item;
- for (item = array->items; item->prog; item++)
+ for (item = array->items; item->prog; item++) {
if (item->prog == old_prog) {
- WRITE_ONCE(item->prog, &dummy_bpf_prog.prog);
- break;
+ WRITE_ONCE(item->prog, new_prog);
+ return 0;
}
+ }
+ return -ENOENT;
+}
+
+void bpf_prog_array_delete_safe(struct bpf_prog_array *array,
+ struct bpf_prog *old_prog)
+{
+ (void)bpf_prog_array_replace_item(array, old_prog,
+ &dummy_bpf_prog.prog);
}
int bpf_prog_array_copy(struct bpf_prog_array *old_array,
diff --git a/kernel/bpf/net_namespace.c b/kernel/bpf/net_namespace.c
index b951dab2687f..593523a22168 100644
--- a/kernel/bpf/net_namespace.c
+++ b/kernel/bpf/net_namespace.c
@@ -38,7 +38,9 @@ static void bpf_netns_link_release(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 *old_array, *new_array;
struct net *net;
+ int err;
/* Link auto-detached by dying netns. */
if (!net_link->net)
@@ -54,8 +56,20 @@ static void bpf_netns_link_release(struct bpf_link *link)
if (!net)
goto out_unlock;
+ /* Rebuild run array without the prog or replace it with a
+ * dummy one because we cannot fail during link release.
+ */
+ old_array = rcu_dereference_protected(net->bpf.run_array[type],
+
lockdep_is_held(&netns_bpf_mutex));
+ err = bpf_prog_array_copy(old_array, link->prog, NULL, &new_array);
+ if (err) {
+ bpf_prog_array_delete_safe(old_array, link->prog);
+ } else {
+ rcu_assign_pointer(net->bpf.run_array[type], new_array);
+ bpf_prog_array_free(old_array);
+ }
+
net->bpf.links[type] = NULL;
- RCU_INIT_POINTER(net->bpf.progs[type], NULL);
out_unlock:
mutex_unlock(&netns_bpf_mutex);
@@ -76,6 +90,7 @@ 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;
@@ -93,8 +108,16 @@ 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));
+ if (run_array)
+ ret = bpf_prog_array_replace_item(run_array, link->prog,
new_prog);
+ else
+ ret = -ENOENT;
+ if (ret)
+ goto out_unlock;
+
old_prog = xchg(&link->prog, new_prog);
- rcu_assign_pointer(net->bpf.progs[type], new_prog);
bpf_prog_put(old_prog);
out_unlock:
@@ -142,14 +165,38 @@ 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;
@@ -162,32 +209,17 @@ 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;
@@ -217,14 +249,25 @@ int netns_bpf_prog_attach(const union bpf_attr *attr,
struct bpf_prog *prog)
if (ret)
goto out_unlock;
- attached = rcu_dereference_protected(net->bpf.progs[type],
- lockdep_is_held(&netns_bpf_mutex));
+ attached = net->bpf.progs[type];
if (attached == prog) {
/* The same program cannot be attached twice */
ret = -EINVAL;
goto out_unlock;
}
- rcu_assign_pointer(net->bpf.progs[type], prog);
+
+ run_array = rcu_dereference_protected(net->bpf.run_array[type],
+
lockdep_is_held(&netns_bpf_mutex));
+ if (run_array) {
+ ret = bpf_prog_array_replace_item(run_array, attached, prog);
+ } else {
+ ret = bpf_prog_array_copy(NULL, NULL, prog, &run_array);
+ rcu_assign_pointer(net->bpf.run_array[type], run_array);
+ }
+ if (ret)
+ goto out_unlock;
+
+ net->bpf.progs[type] = prog;
if (attached)
bpf_prog_put(attached);
@@ -234,6 +277,18 @@ int netns_bpf_prog_attach(const union bpf_attr *attr,
struct bpf_prog *prog)
return ret;
}
+/* Must be called with netns_bpf_mutex held. */
+static void netns_bpf_run_array_detach(struct net *net,
+ enum netns_bpf_attach_type type)
+{
+ struct bpf_prog_array *run_array;
+
+ run_array = rcu_dereference_protected(net->bpf.run_array[type],
+
lockdep_is_held(&netns_bpf_mutex));
+ RCU_INIT_POINTER(net->bpf.run_array[type], NULL);
+ bpf_prog_array_free(run_array);
+}
+
/* Must be called with netns_bpf_mutex held. */
static int __netns_bpf_prog_detach(struct net *net,
enum netns_bpf_attach_type type)
@@ -244,11 +299,11 @@ static int __netns_bpf_prog_detach(struct net *net,
if (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;
}
@@ -272,7 +327,7 @@ 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_prog_array *old_array, *new_array;
int err;
mutex_lock(&netns_bpf_mutex);
@@ -283,9 +338,7 @@ static int netns_bpf_link_attach(struct net *net, struct
bpf_link *link,
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;
}
@@ -301,7 +354,14 @@ static int netns_bpf_link_attach(struct net *net, struct
bpf_link *link,
if (err)
goto out_unlock;
- rcu_assign_pointer(net->bpf.progs[type], link->prog);
+ old_array = rcu_dereference_protected(net->bpf.run_array[type],
+
lockdep_is_held(&netns_bpf_mutex));
+ err = bpf_prog_array_copy(old_array, NULL, link->prog, &new_array);
+ if (err)
+ goto out_unlock;
+ rcu_assign_pointer(net->bpf.run_array[type], new_array);
+ bpf_prog_array_free(old_array);
+
net->bpf.links[type] = link;
out_unlock:
@@ -368,11 +428,12 @@ static void __net_exit netns_bpf_pernet_pre_exit(struct
net *net)
mutex_lock(&netns_bpf_mutex);
for (type = 0; type < MAX_NETNS_BPF_ATTACH_TYPE; type++) {
+ netns_bpf_run_array_detach(net, type);
link = net->bpf.links[type];
if (link)
bpf_netns_link_auto_detach(link);
- else
- __netns_bpf_prog_detach(net, type);
+ else if (net->bpf.progs[type])
+ bpf_prog_put(net->bpf.progs[type]);
}
mutex_unlock(&netns_bpf_mutex);
}
diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c
index b57fb1359395..e501aefb9a0e 100644
--- a/net/core/flow_dissector.c
+++ b/net/core/flow_dissector.c
@@ -86,14 +86,14 @@ int flow_dissector_bpf_prog_attach_check(struct net *net,
for_each_net(ns) {
if (ns == &init_net)
continue;
- if (rcu_access_pointer(ns->bpf.progs[type]))
+ if (rcu_access_pointer(ns->bpf.run_array[type]))
return -EEXIST;
}
} else {
/* Make sure root flow dissector is not attached
* when attaching to the non-root namespace.
*/
- if (rcu_access_pointer(init_net.bpf.progs[type]))
+ if (rcu_access_pointer(init_net.bpf.run_array[type]))
return -EEXIST;
}
@@ -894,7 +894,6 @@ bool __skb_flow_dissect(const struct net *net,
struct flow_dissector_key_addrs *key_addrs;
struct flow_dissector_key_tags *key_tags;
struct flow_dissector_key_vlan *key_vlan;
- struct bpf_prog *attached = NULL;
enum flow_dissect_ret fdret;
enum flow_dissector_key_id dissector_vlan = FLOW_DISSECTOR_KEY_MAX;
bool mpls_el = false;
@@ -951,14 +950,14 @@ bool __skb_flow_dissect(const struct net *net,
WARN_ON_ONCE(!net);
if (net) {
enum netns_bpf_attach_type type = NETNS_BPF_FLOW_DISSECTOR;
+ struct bpf_prog_array *run_array;
rcu_read_lock();
- attached = rcu_dereference(init_net.bpf.progs[type]);
+ run_array = rcu_dereference(init_net.bpf.run_array[type]);
+ if (!run_array)
+ run_array = rcu_dereference(net->bpf.run_array[type]);
- if (!attached)
- attached = rcu_dereference(net->bpf.progs[type]);
-
- if (attached) {
+ if (run_array) {
struct bpf_flow_keys flow_keys;
struct bpf_flow_dissector ctx = {
.flow_keys = &flow_keys,
@@ -966,6 +965,7 @@ bool __skb_flow_dissect(const struct net *net,
.data_end = data + hlen,
};
__be16 n_proto = proto;
+ struct bpf_prog *prog;
if (skb) {
ctx.skb = skb;
@@ -976,8 +976,9 @@ bool __skb_flow_dissect(const struct net *net,
n_proto = skb->protocol;
}
- ret = bpf_flow_dissect(attached, &ctx, n_proto, nhoff,
- hlen, flags);
+ prog = READ_ONCE(run_array->items[0].prog);
+ ret = bpf_flow_dissect(prog, &ctx, n_proto,
+ nhoff, hlen, flags);
__skb_flow_bpf_to_target(&flow_keys, flow_dissector,
target_container);
rcu_read_unlock();
--
2.25.4
