[PATCH 5.15 044/244] bpf: Acquire map uref in .init_seq_private for array map iterator

Greg Kroah-Hartman
2022-08-23T09:47:55Z

From: Hou Tao <houtao1@huawei.com>

commit f76fa6b338055054f80c72b29c97fb95c1becadc upstream.

bpf_iter_attach_map() acquires a map uref, and the uref may be released
before or in the middle of iterating map elements. For example, the uref
could be released in bpf_iter_detach_map() as part of
bpf_link_release(), or could be released in bpf_map_put_with_uref() as
part of bpf_map_release().

Alternative fix is acquiring an extra bpf_link reference just like
a pinned map iterator does, but it introduces unnecessary dependency
on bpf_link instead of bpf_map.

So choose another fix: acquiring an extra map uref in .init_seq_private
for array map iterator.

Fixes: d3cc2ab546ad ("bpf: Implement bpf iterator for array maps")
Signed-off-by: Hou Tao <houtao1@huawei.com>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/r/20220810080538.1845898-2-houtao@huaweicloud.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
kernel/bpf/arraymap.c | 6 ++++++
1 file changed, 6 insertions(+)

--- a/kernel/bpf/arraymap.c
+++ b/kernel/bpf/arraymap.c
@@ -620,6 +620,11 @@ static int bpf_iter_init_array_map(void
seq_info->percpu_value_buf = value_buf;
}

+ /* bpf_iter_attach_map() acquires a map uref, and the uref may be
+ * released before or in the middle of iterating map elements, so
+ * acquire an extra map uref for iterator.
+ */
+ bpf_map_inc_with_uref(map);
seq_info->map = map;
return 0;
}
@@ -628,6 +633,7 @@ static void bpf_iter_fini_array_map(void
{
struct bpf_iter_seq_array_map_info *seq_info = priv_data;

+ bpf_map_put_with_uref(seq_info->map);
kfree(seq_info->percpu_value_buf);
}