From: Martin KaFai Lau <kafai@fb.com>
Date: Mon, 13 Jan 2020 23:26:47 -0800
Subject: bpf: Fix seq_show for BPF_MAP_TYPE_STRUCT_OPS
Patch-mainline: v5.6-rc1
Git-commit: 3b4130418f62b0e7a4685cc2c03bb41c6cb8922d
References: bsc#1177028

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
Acked-by: Gary Lin <glin@suse.com>
---
 kernel/bpf/bpf_struct_ops.c |   14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

--- 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_
 					     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)