netdev - [PATCH bpf-next 3/7] bpf: Free element after unlock in __htab_map_lookup_and_delete

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Message-Id: <20250107085559.3081563-4-houtao@huaweicloud.com>
Date: Tue,  7 Jan 2025 16:55:55 +0800
From: Hou Tao <houtao@...weicloud.com>
To: bpf@...r.kernel.org,
	netdev@...r.kernel.org
Cc: Martin KaFai Lau <martin.lau@...ux.dev>,
	Alexei Starovoitov <alexei.starovoitov@...il.com>,
	Andrii Nakryiko <andrii@...nel.org>,
	Eduard Zingerman <eddyz87@...il.com>,
	Song Liu <song@...nel.org>,
	Hao Luo <haoluo@...gle.com>,
	Yonghong Song <yonghong.song@...ux.dev>,
	Daniel Borkmann <daniel@...earbox.net>,
	KP Singh <kpsingh@...nel.org>,
	Stanislav Fomichev <sdf@...ichev.me>,
	Jiri Olsa <jolsa@...nel.org>,
	John Fastabend <john.fastabend@...il.com>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	houtao1@...wei.com,
	xukuohai@...wei.com
Subject: [PATCH bpf-next 3/7] bpf: Free element after unlock in __htab_map_lookup_and_delete_elem()

From: Hou Tao <houtao1@...wei.com>

The freeing of special fields in map value may acquire a spin-lock
(e.g., the freeing of bpf_timer), however, the lookup_and_delete_elem
procedure has already held a raw-spin-lock, which violates the lockdep
rule.

The running context of __htab_map_lookup_and_delete_elem() has already
disabled the migration. Therefore, it is OK to invoke free_htab_elem()
after unlocking the bucket lock.

Fix the potential problem by freeing element after unlocking bucket lock
in __htab_map_lookup_and_delete_elem().

Signed-off-by: Hou Tao <houtao1@...wei.com>
---
 kernel/bpf/hashtab.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index 59eb117908c5..903447a340d3 100644
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -1669,14 +1669,16 @@ static int __htab_map_lookup_and_delete_elem(struct bpf_map *map, void *key,
 		check_and_init_map_value(map, value);
 	}
 	hlist_nulls_del_rcu(&l->hash_node);
-	if (!is_lru_map)
-		free_htab_elem(htab, l);
 
 out_unlock:
 	htab_unlock_bucket(htab, b, hash, bflags);
 
-	if (is_lru_map && l)
-		htab_lru_push_free(htab, l);
+	if (l) {
+		if (is_lru_map)
+			htab_lru_push_free(htab, l);
+		else
+			free_htab_elem(htab, l);
+	}
 
 	return ret;
 }
-- 
2.29.2