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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
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Jakub Sitnicki authored and Alexei Starovoitov committed Jun 30, 2020
1 parent 3b70169 commit 695c121
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Showing 3 changed files with 96 additions and 48 deletions.
5 changes: 4 additions & 1 deletion include/net/netns/bpf.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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];
};

Expand Down
120 changes: 82 additions & 38 deletions kernel/bpf/net_namespace.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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 =
Expand All @@ -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);
Expand All @@ -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;

Expand All @@ -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:
Expand Down Expand Up @@ -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;
Expand All @@ -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;
Expand Down Expand Up @@ -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);

Expand All @@ -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;
}
Expand All @@ -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);
Expand All @@ -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;
}
Expand All @@ -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:
Expand Down Expand Up @@ -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);
}
Expand Down
19 changes: 10 additions & 9 deletions net/core/flow_dissector.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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;
}

Expand Down Expand Up @@ -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;
Expand Down Expand Up @@ -951,21 +950,22 @@ 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,
.data = data,
.data_end = data + hlen,
};
__be16 n_proto = proto;
struct bpf_prog *prog;

if (skb) {
ctx.skb = skb;
Expand All @@ -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);
Expand Down

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