netdev - [PATCH] bpf: fix filed access without lock

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Message-ID: <20241021013705.14105-1-mrpre@163.com>
Date: Mon, 21 Oct 2024 09:37:05 +0800
From: mrpre <mrpre@....com>
To: edumazet@...gle.com,
	jakub@...udflare.com,
	davem@...emloft.net,
	dsahern@...nel.org,
	kuba@...nel.org,
	pabeni@...hat.com,
	netdev@...r.kernel.org,
	bpf@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc: mrpre <mrpre@....com>
Subject: [PATCH] bpf: fix filed access without lock

The tcp_bpf_recvmsg_parser() function, running in user context,
retrieves seq_copied from tcp_sk without holding the socket lock, and
stores it in a local variable seq. However, the softirq context can
modify tcp_sk->seq_copied concurrently, for example, n tcp_read_sock().

As a result, the seq value is stale when it is assigned back to
tcp_sk->copied_seq at the end of tcp_bpf_recvmsg_parser(), leading to
incorrect behavior.

Signed-off-by: mrpre <mrpre@....com>
---
 net/ipv4/tcp_bpf.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/net/ipv4/tcp_bpf.c b/net/ipv4/tcp_bpf.c
index e7658c5d6b79..7b44d4ece8b2 100644
--- a/net/ipv4/tcp_bpf.c
+++ b/net/ipv4/tcp_bpf.c
@@ -221,9 +221,9 @@ static int tcp_bpf_recvmsg_parser(struct sock *sk,
 				  int flags,
 				  int *addr_len)
 {
-	struct tcp_sock *tcp = tcp_sk(sk);
+	struct tcp_sock *tcp;
+	u32 seq;
 	int peek = flags & MSG_PEEK;
-	u32 seq = tcp->copied_seq;
 	struct sk_psock *psock;
 	int copied = 0;
 
@@ -238,7 +238,8 @@ static int tcp_bpf_recvmsg_parser(struct sock *sk,
 		return tcp_recvmsg(sk, msg, len, flags, addr_len);
 
 	lock_sock(sk);
-
+	tcp = tcp_sk(sk);
+	seq = tcp->copied_seq;
 	/* We may have received data on the sk_receive_queue pre-accept and
 	 * then we can not use read_skb in this context because we haven't
 	 * assigned a sk_socket yet so have no link to the ops. The work-around
-- 
2.43.5