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 7AFB951AFED; Wed, 30 Sep 2026 18:21:17 +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=1790792479; cv=none; b=R+D4A2yePtqFXmEjpYJYaBlLFm+COvlvoMJeLkmc3nxJCh1jlLoXzpWf9brbsmwpYcczhSon/+9keh/z5LlX+Ib0QzHYUpgdbrQjGNiTtcnpkeuJWpqwx+aFNU4BpLcJHJX4cM9pdi9N87wrHSEfrTm2TaTV6SSasi0foQgjQcg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790792479; c=relaxed/simple; bh=uoj6WBWxdXuTvtE3Vycz7d2bEr0Wco+R0df84aRK3ZY=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=MGmxxKPEQwq+YZB5p3aNNdBkTrhma6+B8/YT2721yR/ABLxcZDL08V2D96LHeaVb8ji5vZKHz2jpSzhm3e3e05tbGrsoltm7VVHHqRwx/Z1gdMbuxI5d7zJ+e2voVAoOz5ViYaJAcld9Q9ifqB/IJebCTG4NnHgZ71v5qrzzTaI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=0J67HVi6; 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="0J67HVi6" Received: by smtp.kernel.org (Postfix) with ESMTPSA id DBA861F000FF; Wed, 30 Sep 2026 18:21:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1790792477; bh=t0aiVvJiiOQwxE8JSP2J6XYHk3XnXOV7SoN0qPpHRuA=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=0J67HVi6bgHu+bsyip6MxP5Vj6WgIpDH5pn7AuZa+a7iARFApU2nSHKl04DmqIOkO 09nejMbXlgqnl6iwdQX3TZYShUrC1n7c36qTpD75PdaeAaiC8jR2fnxwoHIj3JWbNl 2cqreFB9qodQyT2AKUean4HPX0D0kuTYXckhSrJU= 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 5.15 670/752] tcp: fix use-after-free of retransmit_skb_hint in tcp_send_synack() Date: Wed, 30 Sep 2026 17:29:00 +0200 Message-ID: <20260930152412.750507530@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260930152358.131179731@linuxfoundation.org> References: <20260930152358.131179731@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 5.15-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 d730a3709f85e..7ebd8c88d2ab3 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -3512,6 +3512,7 @@ void tcp_send_active_reset(struct sock *sk, gfp_t priority) */ int tcp_send_synack(struct sock *sk) { + struct tcp_sock *tp = tcp_sk(sk); struct sk_buff *skb; skb = tcp_rtx_queue_head(sk); @@ -3529,6 +3530,8 @@ 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