linux-kernel - [PATCH AUTOSEL 6.11 20/21] bpf: fix filed access without lock

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Message-ID: <20241104105048.96444-20-sashal@kernel.org>
Date: Mon,  4 Nov 2024 05:49:56 -0500
From: Sasha Levin <sashal@...nel.org>
To: linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Cc: Jiayuan Chen <mrpre@....com>,
	Martin KaFai Lau <martin.lau@...nel.org>,
	Sasha Levin <sashal@...nel.org>,
	edumazet@...gle.com,
	john.fastabend@...il.com,
	jakub@...udflare.com,
	davem@...emloft.net,
	dsahern@...nel.org,
	kuba@...nel.org,
	pabeni@...hat.com,
	netdev@...r.kernel.org,
	bpf@...r.kernel.org
Subject: [PATCH AUTOSEL 6.11 20/21] bpf: fix filed access without lock

From: Jiayuan Chen <mrpre@....com>

[ Upstream commit a32aee8f0d987a7cba7fcc28002553361a392048 ]

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.

Due to concurrency, the copied_seq field in tcp_bpf_recvmsg_parser()
might be set to an incorrect value (less than the actual copied_seq) at
the end of function: 'WRITE_ONCE(tcp->copied_seq, seq)'. This causes the
'offset' to be negative in tcp_read_sock()->tcp_recv_skb() when
processing new incoming packets (sk->copied_seq - skb->seq becomes less
than 0), and all subsequent packets will be dropped.

Signed-off-by: Jiayuan Chen <mrpre@....com>
Link: https://lore.kernel.org/r/20241028065226.35568-1-mrpre@163.com
Signed-off-by: Martin KaFai Lau <martin.lau@...nel.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 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 fe6178715ba05..915286c3615a2 100644
--- a/net/ipv4/tcp_bpf.c
+++ b/net/ipv4/tcp_bpf.c
@@ -221,11 +221,11 @@ static int tcp_bpf_recvmsg_parser(struct sock *sk,
 				  int flags,
 				  int *addr_len)
 {
-	struct tcp_sock *tcp = tcp_sk(sk);
 	int peek = flags & MSG_PEEK;
-	u32 seq = tcp->copied_seq;
 	struct sk_psock *psock;
+	struct tcp_sock *tcp;
 	int copied = 0;
+	u32 seq;

 	if (unlikely(flags & MSG_ERRQUEUE))
 		return inet_recv_error(sk, msg, len, addr_len);
@@ -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
-- 
2.43.0