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bpf, netns: Keep attached programs in bpf_prog_array

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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
This commit is contained in:
Jakub Sitnicki 2020-06-25 16:13:55 +02:00 committed by Alexei Starovoitov
parent 3b7016996c
commit 695c12147a
3 changed files with 96 additions and 48 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
include/net/netns/bpf.h
View File

@ -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];
};

120
kernel/bpf/net_namespace.c
View File

@ -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);
}

19
net/core/flow_dissector.c
View File

@ -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);