bpf: Fix seq_show for BPF_MAP_TYPE_STRUCT_OPS

Instead of using bpf_struct_ops_map_lookup_elem() which is
not implemented, bpf_struct_ops_map_seq_show_elem() should
also use bpf_struct_ops_map_sys_lookup_elem() which does
an inplace update to the value.  The change allocates
a value to pass to bpf_struct_ops_map_sys_lookup_elem().

[root@arch-fb-vm1 bpf]# cat /sys/fs/bpf/dctcp
{{{1}},BPF_STRUCT_OPS_STATE_INUSE,{{00000000df93eebc,00000000df93eebc},0,2, ...

Fixes: 85d33df357b6 ("bpf: Introduce BPF_MAP_TYPE_STRUCT_OPS")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200114072647.3188298-1-kafai@fb.com

diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c
index ddf48f4..8ad1c9e 100644 (file)
--- a/kernel/bpf/bpf_struct_ops.c
+++ b/kernel/bpf/bpf_struct_ops.c
@@ -496,14 +496,20 @@ static void bpf_struct_ops_map_seq_show_elem(struct bpf_map *map, void *key,
                                             struct seq_file *m)
 {
        void *value;
+       int err;
 
-       value = bpf_struct_ops_map_lookup_elem(map, key);
+       value = kmalloc(map->value_size, GFP_USER | __GFP_NOWARN);
        if (!value)
                return;
 
-       btf_type_seq_show(btf_vmlinux, map->btf_vmlinux_value_type_id,
-                         value, m);
-       seq_puts(m, "\n");
+       err = bpf_struct_ops_map_sys_lookup_elem(map, key, value);
+       if (!err) {
+               btf_type_seq_show(btf_vmlinux, map->btf_vmlinux_value_type_id,
+                                 value, m);
+               seq_puts(m, "\n");
+       }
+
+       kfree(value);
 }
 
 static void bpf_struct_ops_map_free(struct bpf_map *map)