netdev - [PATCH net-next 1/8] tcp: do not accept packets beyond window

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20250711114006.480026-2-edumazet@google.com>
Date: Fri, 11 Jul 2025 11:39:59 +0000
From: Eric Dumazet <edumazet@...gle.com>
To: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>, Neal Cardwell <ncardwell@...gle.com>
Cc: Simon Horman <horms@...nel.org>, Kuniyuki Iwashima <kuniyu@...gle.com>, 
	Willem de Bruijn <willemb@...gle.com>, netdev@...r.kernel.org, eric.dumazet@...il.com, 
	Eric Dumazet <edumazet@...gle.com>
Subject: [PATCH net-next 1/8] tcp: do not accept packets beyond window

Currently, TCP accepts incoming packets which might go beyond the
offered RWIN.

Add to tcp_sequence() the validation of packet end sequence.

Add the corresponding check in the fast path.

We relax this new constraint if the receive queue is empty,
to not freeze flows from buggy peers.

Add a new drop reason : SKB_DROP_REASON_TCP_INVALID_END_SEQUENCE.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 include/net/dropreason-core.h |  7 ++++++-
 net/ipv4/tcp_input.c          | 22 +++++++++++++++++-----
 2 files changed, 23 insertions(+), 6 deletions(-)

diff --git a/include/net/dropreason-core.h b/include/net/dropreason-core.h
index b9e78290269e6e7d9d9155171f6b0ef03c7697c9..d88ff9a75d15fe60a961332a7eb4be94c5c7c3ec 100644
--- a/include/net/dropreason-core.h
+++ b/include/net/dropreason-core.h
@@ -45,6 +45,7 @@
 	FN(TCP_LISTEN_OVERFLOW)		\
 	FN(TCP_OLD_SEQUENCE)		\
 	FN(TCP_INVALID_SEQUENCE)	\
+	FN(TCP_INVALID_END_SEQUENCE)	\
 	FN(TCP_INVALID_ACK_SEQUENCE)	\
 	FN(TCP_RESET)			\
 	FN(TCP_INVALID_SYN)		\
@@ -303,8 +304,12 @@ enum skb_drop_reason {
 	SKB_DROP_REASON_TCP_LISTEN_OVERFLOW,
 	/** @SKB_DROP_REASON_TCP_OLD_SEQUENCE: Old SEQ field (duplicate packet) */
 	SKB_DROP_REASON_TCP_OLD_SEQUENCE,
-	/** @SKB_DROP_REASON_TCP_INVALID_SEQUENCE: Not acceptable SEQ field */
+	/** @SKB_DROP_REASON_TCP_INVALID_SEQUENCE: Not acceptable SEQ field.
+	 */
 	SKB_DROP_REASON_TCP_INVALID_SEQUENCE,
+	/** @SKB_DROP_REASON_TCP_INVALID_END_SEQUENCE: Not acceptable END_SEQ field.
+	 */
+	SKB_DROP_REASON_TCP_INVALID_END_SEQUENCE,
 	/**
 	 * @SKB_DROP_REASON_TCP_INVALID_ACK_SEQUENCE: Not acceptable ACK SEQ
 	 * field because ack sequence is not in the window between snd_una
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 9b03c44c12b862b5d33f4390cfc85e2f8897cd8e..f0f9c78654b449cb2a122e8c53fdcc96e5317de7 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -4391,14 +4391,22 @@ static enum skb_drop_reason tcp_disordered_ack_check(const struct sock *sk,
  * (borrowed from freebsd)
  */
 
-static enum skb_drop_reason tcp_sequence(const struct tcp_sock *tp,
+static enum skb_drop_reason tcp_sequence(const struct sock *sk,
 					 u32 seq, u32 end_seq)
 {
+	const struct tcp_sock *tp = tcp_sk(sk);
+
 	if (before(end_seq, tp->rcv_wup))
 		return SKB_DROP_REASON_TCP_OLD_SEQUENCE;
 
-	if (after(seq, tp->rcv_nxt + tcp_receive_window(tp)))
-		return SKB_DROP_REASON_TCP_INVALID_SEQUENCE;
+	if (after(end_seq, tp->rcv_nxt + tcp_receive_window(tp))) {
+		if (after(seq, tp->rcv_nxt + tcp_receive_window(tp)))
+			return SKB_DROP_REASON_TCP_INVALID_SEQUENCE;
+
+		/* Only accept this packet if receive queue is empty. */
+		if (skb_queue_len(&sk->sk_receive_queue))
+			return SKB_DROP_REASON_TCP_INVALID_END_SEQUENCE;
+	}
 
 	return SKB_NOT_DROPPED_YET;
 }
@@ -5881,7 +5889,7 @@ static bool tcp_validate_incoming(struct sock *sk, struct sk_buff *skb,
 
 step1:
 	/* Step 1: check sequence number */
-	reason = tcp_sequence(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
+	reason = tcp_sequence(sk, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
 	if (reason) {
 		/* RFC793, page 37: "In all states except SYN-SENT, all reset
 		 * (RST) segments are validated by checking their SEQ-fields."
@@ -6110,6 +6118,10 @@ void tcp_rcv_established(struct sock *sk, struct sk_buff *skb)
 			if (tcp_checksum_complete(skb))
 				goto csum_error;
 
+			if (after(TCP_SKB_CB(skb)->end_seq,
+				  tp->rcv_nxt + tcp_receive_window(tp)))
+				goto validate;
+
 			if ((int)skb->truesize > sk->sk_forward_alloc)
 				goto step5;
 
@@ -6165,7 +6177,7 @@ void tcp_rcv_established(struct sock *sk, struct sk_buff *skb)
 	/*
 	 *	Standard slow path.
 	 */
-
+validate:
 	if (!tcp_validate_incoming(sk, skb, th, 1))
 		return;
 
-- 
2.50.0.727.gbf7dc18ff4-goog