bpf: fix bpffs non-array map seq_show issue

In function map_seq_next() of kernel/bpf/inode.c,
the first key will be the "0" regardless of the map type.
This works for array. But for hash type, if it happens
key "0" is in the map, the bpffs map show will miss
some items if the key "0" is not the first element of
the first bucket.

This patch fixed the issue by guaranteeing to get
the first element, if the seq_show is just started,
by passing NULL pointer key to map_get_next_key() callback.
This way, no missing elements will occur for
bpffs hash table show even if key "0" is in the map.

Fixes: a26ca7c982cb5 ("bpf: btf: Add pretty print support to the basic arraymap")
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

diff --git a/kernel/bpf/inode.c b/kernel/bpf/inode.c
index 76efe9a183f5313de5cc0b43f2bc4fc446d9bf6a..fc5b103512e7231b1542e4495189721b7728da31 100644 (file)
--- a/kernel/bpf/inode.c
+++ b/kernel/bpf/inode.c
@@ -196,19 +196,21 @@ static void *map_seq_next(struct seq_file *m, void *v, loff_t *pos)
 {
        struct bpf_map *map = seq_file_to_map(m);
        void *key = map_iter(m)->key;
+       void *prev_key;
 
        if (map_iter(m)->done)
                return NULL;
 
        if (unlikely(v == SEQ_START_TOKEN))
-               goto done;
+               prev_key = NULL;
+       else
+               prev_key = key;
 
-       if (map->ops->map_get_next_key(map, key, key)) {
+       if (map->ops->map_get_next_key(map, prev_key, key)) {
                map_iter(m)->done = true;
                return NULL;
        }
 
-done:
        ++(*pos);
        return key;
 }