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bpf, netns: Handle multiple link attachments
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Extend the BPF netns link callbacks to rebuild (grow/shrink) or update the
prog_array at given position when link gets attached/updated/released.

This let's us lift the limit of having just one link attached for the new
attach type introduced by subsequent patch.

No functional changes intended.

Signed-off-by: Jakub Sitnicki <[email protected]>
Signed-off-by: Alexei Starovoitov <[email protected]>
Acked-by: Andrii Nakryiko <[email protected]>
Link: https://lore.kernel.org/bpf/[email protected]
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@jsitnicki
jsitnicki authored and Alexei Starovoitov committed Jul 18, 2020
1 parent bfdfa51 commit ce3aa9c
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Showing 3 changed files with 139 additions and 9 deletions.
3 changes: 3 additions & 0 deletions include/linux/bpf.h
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Original file line number Diff line number Diff line change
Expand Up @@ -928,6 +928,9 @@ int bpf_prog_array_copy_to_user(struct bpf_prog_array *progs,

void bpf_prog_array_delete_safe(struct bpf_prog_array *progs,
struct bpf_prog *old_prog);
int bpf_prog_array_delete_safe_at(struct bpf_prog_array *array, int index);
int bpf_prog_array_update_at(struct bpf_prog_array *array, int index,
struct bpf_prog *prog);
int bpf_prog_array_copy_info(struct bpf_prog_array *array,
u32 *prog_ids, u32 request_cnt,
u32 *prog_cnt);
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55 changes: 55 additions & 0 deletions kernel/bpf/core.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1958,6 +1958,61 @@ void bpf_prog_array_delete_safe(struct bpf_prog_array *array,
}
}

/**
* bpf_prog_array_delete_safe_at() - Replaces the program at the given
* index into the program array with
* a dummy no-op program.
* @array: a bpf_prog_array
* @index: the index of the program to replace
*
* Skips over dummy programs, by not counting them, when calculating
* the the position of the program to replace.
*
* Return:
* * 0 - Success
* * -EINVAL - Invalid index value. Must be a non-negative integer.
* * -ENOENT - Index out of range
*/
int bpf_prog_array_delete_safe_at(struct bpf_prog_array *array, int index)
{
return bpf_prog_array_update_at(array, index, &dummy_bpf_prog.prog);
}

/**
* bpf_prog_array_update_at() - Updates the program at the given index
* into the program array.
* @array: a bpf_prog_array
* @index: the index of the program to update
* @prog: the program to insert into the array
*
* Skips over dummy programs, by not counting them, when calculating
* the position of the program to update.
*
* Return:
* * 0 - Success
* * -EINVAL - Invalid index value. Must be a non-negative integer.
* * -ENOENT - Index out of range
*/
int bpf_prog_array_update_at(struct bpf_prog_array *array, int index,
struct bpf_prog *prog)
{
struct bpf_prog_array_item *item;

if (unlikely(index < 0))
return -EINVAL;

for (item = array->items; item->prog; item++) {
if (item->prog == &dummy_bpf_prog.prog)
continue;
if (!index) {
WRITE_ONCE(item->prog, prog);
return 0;
}
index--;
}
return -ENOENT;
}

int bpf_prog_array_copy(struct bpf_prog_array *old_array,
struct bpf_prog *exclude_prog,
struct bpf_prog *include_prog,
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90 changes: 81 additions & 9 deletions kernel/bpf/net_namespace.c
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Original file line number Diff line number Diff line change
Expand Up @@ -36,12 +36,50 @@ static void netns_bpf_run_array_detach(struct net *net,
bpf_prog_array_free(run_array);
}

static int link_index(struct net *net, enum netns_bpf_attach_type type,
struct bpf_netns_link *link)
{
struct bpf_netns_link *pos;
int i = 0;

list_for_each_entry(pos, &net->bpf.links[type], node) {
if (pos == link)
return i;
i++;
}
return -ENOENT;
}

static int link_count(struct net *net, enum netns_bpf_attach_type type)
{
struct list_head *pos;
int i = 0;

list_for_each(pos, &net->bpf.links[type])
i++;
return i;
}

static void fill_prog_array(struct net *net, enum netns_bpf_attach_type type,
struct bpf_prog_array *prog_array)
{
struct bpf_netns_link *pos;
unsigned int i = 0;

list_for_each_entry(pos, &net->bpf.links[type], node) {
prog_array->items[i].prog = pos->link.prog;
i++;
}
}

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 cnt, idx;

mutex_lock(&netns_bpf_mutex);

Expand All @@ -53,9 +91,27 @@ static void bpf_netns_link_release(struct bpf_link *link)
if (!net)
goto out_unlock;

netns_bpf_run_array_detach(net, type);
/* Remember link position in case of safe delete */
idx = link_index(net, type, net_link);
list_del(&net_link->node);

cnt = link_count(net, type);
if (!cnt) {
netns_bpf_run_array_detach(net, type);
goto out_unlock;
}

old_array = rcu_dereference_protected(net->bpf.run_array[type],
lockdep_is_held(&netns_bpf_mutex));
new_array = bpf_prog_array_alloc(cnt, GFP_KERNEL);
if (!new_array) {
WARN_ON(bpf_prog_array_delete_safe_at(old_array, idx));
goto out_unlock;
}
fill_prog_array(net, type, new_array);
rcu_assign_pointer(net->bpf.run_array[type], new_array);
bpf_prog_array_free(old_array);

out_unlock:
mutex_unlock(&netns_bpf_mutex);
}
Expand All @@ -77,7 +133,7 @@ static int bpf_netns_link_update_prog(struct bpf_link *link,
enum netns_bpf_attach_type type = net_link->netns_type;
struct bpf_prog_array *run_array;
struct net *net;
int ret = 0;
int idx, ret;

if (old_prog && old_prog != link->prog)
return -EPERM;
Expand All @@ -95,7 +151,10 @@ static int bpf_netns_link_update_prog(struct bpf_link *link,

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);
idx = link_index(net, type, net_link);
ret = bpf_prog_array_update_at(run_array, idx, new_prog);
if (ret)
goto out_unlock;

old_prog = xchg(&link->prog, new_prog);
bpf_prog_put(old_prog);
Expand Down Expand Up @@ -309,18 +368,28 @@ int netns_bpf_prog_detach(const union bpf_attr *attr, enum bpf_prog_type ptype)
return ret;
}

static int netns_bpf_max_progs(enum netns_bpf_attach_type type)
{
switch (type) {
case NETNS_BPF_FLOW_DISSECTOR:
return 1;
default:
return 0;
}
}

static int netns_bpf_link_attach(struct net *net, struct bpf_link *link,
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;
int err;
int cnt, err;

mutex_lock(&netns_bpf_mutex);

/* Allow attaching only one prog or link for now */
if (!list_empty(&net->bpf.links[type])) {
cnt = link_count(net, type);
if (cnt >= netns_bpf_max_progs(type)) {
err = -E2BIG;
goto out_unlock;
}
Expand All @@ -341,16 +410,19 @@ static int netns_bpf_link_attach(struct net *net, struct bpf_link *link,
if (err)
goto out_unlock;

run_array = bpf_prog_array_alloc(1, GFP_KERNEL);
run_array = bpf_prog_array_alloc(cnt + 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]);

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

out_unlock:
mutex_unlock(&netns_bpf_mutex);
return err;
Expand Down

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