linux-kernel - [PATCH 5.10 027/158] bpf: Acquire map uref in .init_seq

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Message-Id: <20220823080047.190919503@linuxfoundation.org>
Date:   Tue, 23 Aug 2022 10:25:59 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Hou Tao <houtao1@...wei.com>,
        Yonghong Song <yhs@...com>, Alexei Starovoitov <ast@...nel.org>
Subject: [PATCH 5.10 027/158] bpf: Acquire map uref in .init_seq_private for array map iterator

From: Hou Tao <houtao1@...wei.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@...wei.com>
Acked-by: Yonghong Song <yhs@...com>
Link: https://lore.kernel.org/r/20220810080538.1845898-2-houtao@huaweicloud.com
Signed-off-by: Alexei Starovoitov <ast@...nel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 kernel/bpf/arraymap.c |    6 ++++++
 1 file changed, 6 insertions(+)

--- a/kernel/bpf/arraymap.c
+++ b/kernel/bpf/arraymap.c
@@ -616,6 +616,11 @@ 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;
 }
@@ -624,6 +629,7 @@ 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);
 }