[PATCH bpf 1/9] bpf: Acquire map uref in .init_seq_private for array map iterator

[Hou Tao <houtao@xxxxxxxxxxxxxxx>]

From: Hou Tao <houtao1@xxxxxxxxxx>

During bpf(BPF_LINK_CREATE) for BPF_TRACE_ITER, bpf_iter_attach_map()
has already acquired a map uref, but the uref may be released by
bpf_link_release() during th reading of map iterator.

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@xxxxxxxxxx>
---
 kernel/bpf/arraymap.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c
index d3e734bf8056..bf6898bb7cb8 100644
--- a/kernel/bpf/arraymap.c
+++ b/kernel/bpf/arraymap.c
@@ -649,6 +649,12 @@ static int bpf_iter_init_array_map(void *priv_data,
 		seq_info->percpu_value_buf = value_buf;
 	}
 
+	/*
+	 * During bpf(BPF_LINK_CREATE), bpf_iter_attach_map() has already
+	 * acquired a map uref, but the uref may be released by
+	 * bpf_link_release(), so acquire an extra map uref for iterator.
+	 */
+	bpf_map_inc_with_uref(map);
 	seq_info->map = map;
 	return 0;
 }
@@ -657,6 +663,7 @@ static void bpf_iter_fini_array_map(void *priv_data)
 {
 	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);
 }
 
-- 
2.29.2