From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B513B51AEEE; Wed, 30 Sep 2026 17:28:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790789335; cv=none; b=h1vOeYdNnjLet/XOWb3uUYoIC5d5lF7aJBQLqB5mFCUVjWkahs/UyWXGHELaVGVrqHcu2HElEQtGxHmyNtjbd62hNYBdoXmK1qrLyDZodEioZXpLnhMfRtERfyW2hukCEZpXdZ5icvZMmYeQ8bSd2wWZS8RyAbhs6GsatX64mFs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790789335; c=relaxed/simple; bh=kNQDJgPM9XpLs/HnoIKBRM0FmvLvfANmkludSb9E+QU=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=RnAxw56xLjDLy+WYUr9bECh/IGSGxfmBmP2FiZBEQxXyYBXXSoaUcN3SErl+9ALmgVpcjRMXpk42mp10+8u8AHGVGgYEi9CXXyo9ruYi7z4uJ1GWac8xAkj62VMJC9ImXDV2/O/svgGeLPnIaqScSRifrYL9YCWUuSr1MMPoTzU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=isuOUDLR; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="isuOUDLR" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 21A401F000FF; Wed, 30 Sep 2026 17:28:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1790789334; bh=kI4LICaH99Qv86SQRi7A0nXx4GjQKZCNDjhoEvX2twY=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=isuOUDLRjhm0WXjdY8CsP79pzZpXBpAyUdb0Yj6l1+E6RGlXHdBnNyJJIJnY4UPQS AGbUmBVNadQDRbDks7U4bhSp2mI7j9cO6dfY4fWuRGKQy34zk48GHY5Zb2qGRHlw3B 7Uf47q/UD/H8Rgt00gQIQcG6O8E90IjqZAmRGlm8= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Kimi Security Team , Weiming Shi , Yilin Zhang , Eric Dumazet , Jakub Kicinski , Sasha Levin Subject: [PATCH 6.12 439/877] tcp: fix use-after-free of retransmit_skb_hint in tcp_send_synack() Date: Wed, 30 Sep 2026 17:22:30 +0200 Message-ID: <20260930152424.156921757@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260930152414.738996857@linuxfoundation.org> References: <20260930152414.738996857@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: Yilin Zhang [ Upstream commit fe99bbeee5c5dbd3abc30721a8079ced59649d97 ] When tcp_send_synack() replaces the cloned SYN skb at the head of the retransmit queue with a copy, it frees the original with tcp_rtx_queue_unlink_and_free() and only repairs tp->highest_sack. tp->retransmit_skb_hint keeps pointing at the freed skbuff_fclone_cache object. The dangling hint is read in tcp_verify_retransmit_hint() and used as the root of the rbtree walk in tcp_xmit_retransmit_queue(). An unprivileged TFO client (sendmsg(MSG_FASTOPEN)) can arm the hint with an attacker-supplied ICMP fragmentation-needed message, after which a simultaneous open frees the armed SYN skb: BUG: KASAN: slab-use-after-free in tcp_mark_skb_lost (net/ipv4/tcp_input.c:1316) Read of size 4 at addr ffff88800604d928 by task swapper/1/0 Call Trace: tcp_mark_skb_lost (net/ipv4/tcp_input.c:1316) tcp_simple_retransmit (net/ipv4/tcp_input.c:3158) tcp_v4_err (net/ipv4/tcp_ipv4.c:587) Sync the hint to the copy. Fixes: c31b70c9968f ("tcp: Add logic to check for SYN w/ data in tcp_simple_retransmit") Reported-by: Kimi Security Team Tested-by: Weiming Shi Signed-off-by: Yilin Zhang Reviewed-by: Eric Dumazet Link: https://patch.msgid.link/8a9dff4063a2745653b7e88ceb745d75efa16e68.1790224474.git.yilinzhang@moonshot.ai Signed-off-by: Jakub Kicinski Signed-off-by: Sasha Levin --- net/ipv4/tcp_output.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index a8c4801228677..aa00a9fb2506c 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -3679,6 +3679,7 @@ void tcp_send_active_reset(struct sock *sk, enum sk_rst_reason reason) */ int tcp_send_synack(struct sock *sk) { + struct tcp_sock *tp = tcp_sk(sk); struct sk_buff *skb; skb = tcp_rtx_queue_head(sk); @@ -3696,6 +3697,8 @@ int tcp_send_synack(struct sock *sk) if (!nskb) return -ENOMEM; INIT_LIST_HEAD(&nskb->tcp_tsorted_anchor); + if (skb == tp->retransmit_skb_hint) + tp->retransmit_skb_hint = nskb; tcp_highest_sack_replace(sk, skb, nskb); tcp_rtx_queue_unlink_and_free(skb, sk); __skb_header_release(nskb); -- 2.53.0