bpf: Add syscall lookup support for fd array and htab

This patch allows userspace to do BPF_MAP_LOOKUP_ELEM on
BPF_MAP_TYPE_PROG_ARRAY,
BPF_MAP_TYPE_ARRAY_OF_MAPS and
BPF_MAP_TYPE_HASH_OF_MAPS.

The lookup returns a prog-id or map-id to the userspace.
The userspace can then use the BPF_PROG_GET_FD_BY_ID
or BPF_MAP_GET_FD_BY_ID to get a fd.

Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 13 insertions, 3 deletions

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 8942c820d620..4409ccca8831 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -24,6 +24,13 @@
 #include <linux/kernel.h>
 #include <linux/idr.h>
 
+#define IS_FD_ARRAY(map) ((map)->map_type == BPF_MAP_TYPE_PROG_ARRAY || \
+                           (map)->map_type == BPF_MAP_TYPE_PERF_EVENT_ARRAY || \
+                           (map)->map_type == BPF_MAP_TYPE_CGROUP_ARRAY || \
+                           (map)->map_type == BPF_MAP_TYPE_ARRAY_OF_MAPS)
+#define IS_FD_HASH(map) ((map)->map_type == BPF_MAP_TYPE_HASH_OF_MAPS)
+#define IS_FD_MAP(map) (IS_FD_ARRAY(map) || IS_FD_HASH(map))
+
 DEFINE_PER_CPU(int, bpf_prog_active);
 static DEFINE_IDR(prog_idr);
 static DEFINE_SPINLOCK(prog_idr_lock);
@@ -411,6 +418,8 @@ static int map_lookup_elem(union bpf_attr *attr)
             map->map_type == BPF_MAP_TYPE_LRU_PERCPU_HASH ||
             map->map_type == BPF_MAP_TYPE_PERCPU_ARRAY)
                 value_size = round_up(map->value_size, 8) * num_possible_cpus();
+        else if (IS_FD_MAP(map))
+                value_size = sizeof(u32);
         else
                 value_size = map->value_size;
 
@@ -426,9 +435,10 @@ static int map_lookup_elem(union bpf_attr *attr)
                 err = bpf_percpu_array_copy(map, key, value);
         } else if (map->map_type == BPF_MAP_TYPE_STACK_TRACE) {
                 err = bpf_stackmap_copy(map, key, value);
-        } else if (map->map_type == BPF_MAP_TYPE_ARRAY_OF_MAPS ||
-                   map->map_type == BPF_MAP_TYPE_HASH_OF_MAPS) {
-                err = -ENOTSUPP;
+        } else if (IS_FD_ARRAY(map)) {
+                err = bpf_fd_array_map_lookup_elem(map, key, value);
+        } else if (IS_FD_HASH(map)) {
+                err = bpf_fd_htab_map_lookup_elem(map, key, value);
         } else {
                 rcu_read_lock();
                 ptr = map->ops->map_lookup_elem(map, key);