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, 27 insertions, 0 deletions

diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c
index ecb43542246e..d771a3872500 100644
--- a/kernel/bpf/arraymap.c
+++ b/kernel/bpf/arraymap.c
@@ -335,6 +335,26 @@ static void *fd_array_map_lookup_elem(struct bpf_map *map, void *key)
 }
 
 /* only called from syscall */
+int bpf_fd_array_map_lookup_elem(struct bpf_map *map, void *key, u32 *value)
+{
+        void **elem, *ptr;
+        int ret =  0;
+
+        if (!map->ops->map_fd_sys_lookup_elem)
+                return -ENOTSUPP;
+
+        rcu_read_lock();
+        elem = array_map_lookup_elem(map, key);
+        if (elem && (ptr = READ_ONCE(*elem)))
+                *value = map->ops->map_fd_sys_lookup_elem(ptr);
+        else
+                ret = -ENOENT;
+        rcu_read_unlock();
+
+        return ret;
+}
+
+/* only called from syscall */
 int bpf_fd_array_map_update_elem(struct bpf_map *map, struct file *map_file,
                                  void *key, void *value, u64 map_flags)
 {
@@ -400,6 +420,11 @@ static void prog_fd_array_put_ptr(void *ptr)
         bpf_prog_put(ptr);
 }
 
+static u32 prog_fd_array_sys_lookup_elem(void *ptr)
+{
+        return ((struct bpf_prog *)ptr)->aux->id;
+}
+
 /* decrement refcnt of all bpf_progs that are stored in this map */
 void bpf_fd_array_map_clear(struct bpf_map *map)
 {
@@ -418,6 +443,7 @@ const struct bpf_map_ops prog_array_map_ops = {
         .map_delete_elem = fd_array_map_delete_elem,
         .map_fd_get_ptr = prog_fd_array_get_ptr,
         .map_fd_put_ptr = prog_fd_array_put_ptr,
+        .map_fd_sys_lookup_elem = prog_fd_array_sys_lookup_elem,
 };
 
 static struct bpf_event_entry *bpf_event_entry_gen(struct file *perf_file,
@@ -585,4 +611,5 @@ const struct bpf_map_ops array_of_maps_map_ops = {
         .map_delete_elem = fd_array_map_delete_elem,
         .map_fd_get_ptr = bpf_map_fd_get_ptr,
         .map_fd_put_ptr = bpf_map_fd_put_ptr,
+        .map_fd_sys_lookup_elem = bpf_map_fd_sys_lookup_elem,
 };