bpf, netns: Keep attached programs in bpf_prog_array

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.

After this change bpf(PROG_QUERY) may block to allocate memory in
bpf_prog_array_copy_to_user() for collected program IDs. This forces a
change in how we protect access to the attached program in the query
callback. Because bpf_prog_array_copy_to_user() can sleep, we switch from
an RCU read lock to holding a mutex that serializes updaters.

Because we allow only one BPF flow_dissector program to be attached to
netns at all times, the bpf_prog_array pointed by net->bpf.run_array is
always either detached (null) or one element long.

No functional changes intended.

Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/20200625141357.910330-3-jakub@cloudflare.com

diff --git a/include/net/netns/bpf.h b/include/net/netns/bpf.h
index a8dce2a380c8e85e6c32bbe4244f2bac302e68de..a5015bda997981cdc9b587f99c175b2a004f8de9 100644 (file)
--- 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/net_namespace.c b/kernel/bpf/net_namespace.c
index b951dab2687f861a7fdec63175c75962a99ce28d..0dba972023571edc32b3d4d637d128197d2cf716 100644 (file)
--- a/kernel/bpf/net_namespace.c
+++ b/kernel/bpf/net_namespace.c
@@ -33,6 +33,17 @@ static void __net_exit bpf_netns_link_auto_detach(struct bpf_link *link)
        net_link->net = NULL;
 }
 
+/* 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_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)
 {
        struct bpf_netns_link *net_link =
@@ -54,8 +65,8 @@ static void bpf_netns_link_release(struct bpf_link *link)
        if (!net)
                goto out_unlock;
 
+       netns_bpf_run_array_detach(net, type);
        net->bpf.links[type] = NULL;
-       RCU_INIT_POINTER(net->bpf.progs[type], NULL);
 
 out_unlock:
        mutex_unlock(&netns_bpf_mutex);
@@ -76,6 +87,7 @@ 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 +105,11 @@ 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:
@@ -142,14 +157,38 @@ 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 +201,17 @@ 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 +241,28 @@ 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) {
+               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);
 
@@ -244,11 +282,11 @@ 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 +310,7 @@ 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 *run_array;
        int err;
 
        mutex_lock(&netns_bpf_mutex);
@@ -283,9 +321,7 @@ 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 +337,14 @@ 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);
+       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);
+
        net->bpf.links[type] = link;
 
 out_unlock:
@@ -368,11 +411,12 @@ 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 b57fb13593958c892a2bfdebd80b8038e9ce8bec..142a8824f0a8ef348b56b0497484f1e3af391ae3 100644 (file)
--- 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;
@@ -976,7 +976,8 @@ bool __skb_flow_dissect(const struct net *net,
                                n_proto = skb->protocol;
                        }
 
-                       ret = bpf_flow_dissect(attached, &ctx, n_proto, nhoff,
+                       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);