linux-kernel - [PATCH] bpf: Fix mismatched RCU unlock flavour in bpf_out_neigh

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Message-ID: <tencent_CFD3D1C3D68B45EA9F52D8EC76D2C4134306@qq.com>
Date: Fri,  8 Nov 2024 08:18:52 +0000
From: Jiawei Ye <jiawei.ye@...mail.com>
To: martin.lau@...ux.dev,
	daniel@...earbox.net,
	edumazet@...gle.com,
	kuba@...nel.org
Cc: bpf@...r.kernel.org,
	netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] bpf: Fix mismatched RCU unlock flavour in bpf_out_neigh_v6

In the bpf_out_neigh_v6 function, rcu_read_lock() is used to begin an RCU
read-side critical section. However, when unlocking, one branch
incorrectly uses a different RCU unlock flavour rcu_read_unlock_bh()
instead of rcu_read_unlock(). This mismatch in RCU locking flavours can
lead to unexpected behavior and potential concurrency issues.

This possible bug was identified using a static analysis tool developed
by myself, specifically designed to detect RCU-related issues.

This patch corrects the mismatched unlock flavour by replacing the
incorrect rcu_read_unlock_bh() with the appropriate rcu_read_unlock(),
ensuring that the RCU critical section is properly exited. This change
prevents potential synchronization issues and aligns with proper RCU
usage patterns.

Fixes: 09eed1192cec ("neighbour: switch to standard rcu, instead of rcu_bh")
Signed-off-by: Jiawei Ye <jiawei.ye@...mail.com>
---
 net/core/filter.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/core/filter.c b/net/core/filter.c
index 64248d0ac4ad..44bbc1dbfb50 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -2232,7 +2232,7 @@ static int bpf_out_neigh_v6(struct net *net, struct sk_buff *skb,
 		rcu_read_unlock();
 		return ret;
 	}
-	rcu_read_unlock_bh();
+	rcu_read_unlock();
 	if (dst)
 		IP6_INC_STATS(net, ip6_dst_idev(dst), IPSTATS_MIB_OUTNOROUTES);
 out_drop:
-- 
2.34.1