Commit 1ae80cf3 authored by Daniel Colascione's avatar Daniel Colascione Committed by Alexei Starovoitov

bpf: wait for running BPF programs when updating map-in-map

The map-in-map frequently serves as a mechanism for atomic
snapshotting of state that a BPF program might record.  The current
implementation is dangerous to use in this way, however, since
userspace has no way of knowing when all programs that might have
retrieved the "old" value of the map may have completed.

This change ensures that map update operations on map-in-map map types
always wait for all references to the old map to drop before returning
to userspace.
Signed-off-by: default avatarDaniel Colascione <dancol@google.com>
Reviewed-by: default avatarJoel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent ef4ab844
...@@ -748,6 +748,17 @@ static int map_lookup_elem(union bpf_attr *attr) ...@@ -748,6 +748,17 @@ static int map_lookup_elem(union bpf_attr *attr)
return err; return err;
} }
static void maybe_wait_bpf_programs(struct bpf_map *map)
{
/* Wait for any running BPF programs to complete so that
* userspace, when we return to it, knows that all programs
* that could be running use the new map value.
*/
if (map->map_type == BPF_MAP_TYPE_HASH_OF_MAPS ||
map->map_type == BPF_MAP_TYPE_ARRAY_OF_MAPS)
synchronize_rcu();
}
#define BPF_MAP_UPDATE_ELEM_LAST_FIELD flags #define BPF_MAP_UPDATE_ELEM_LAST_FIELD flags
static int map_update_elem(union bpf_attr *attr) static int map_update_elem(union bpf_attr *attr)
...@@ -842,6 +853,7 @@ static int map_update_elem(union bpf_attr *attr) ...@@ -842,6 +853,7 @@ static int map_update_elem(union bpf_attr *attr)
} }
__this_cpu_dec(bpf_prog_active); __this_cpu_dec(bpf_prog_active);
preempt_enable(); preempt_enable();
maybe_wait_bpf_programs(map);
out: out:
free_value: free_value:
kfree(value); kfree(value);
...@@ -894,6 +906,7 @@ static int map_delete_elem(union bpf_attr *attr) ...@@ -894,6 +906,7 @@ static int map_delete_elem(union bpf_attr *attr)
rcu_read_unlock(); rcu_read_unlock();
__this_cpu_dec(bpf_prog_active); __this_cpu_dec(bpf_prog_active);
preempt_enable(); preempt_enable();
maybe_wait_bpf_programs(map);
out: out:
kfree(key); kfree(key);
err_put: err_put:
......
Markdown is supported
0%
or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment