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 8627123C39A; Wed, 20 May 2026 13:48:46 +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=1779284927; cv=none; b=qlfmxxFBaQYl8ULmLqtDp08dObdSZX4X8+9l3h0FaXVs7Dcl+O6ARamtMepyxnt+VP3tyDgmg4xIxsQRK21E1BDRJZnPpfkSitAZ2MuDOfqvkz1errvb84/KmWHxX+wmPfckue+hBMW8iskSuEl/iGDakLhkJBaKeRwuROMvOrU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779284927; c=relaxed/simple; bh=Q1bXY7UlxwnmfwjlCVNcMh70j2jjziqp16h8olKSqlw=; h=From:To:Subject:Date:Message-ID:MIME-Version; b=dKOVhw7lDICqpQRkF9s+s4fSwnOnzgf4bVuiwEPQTqAWZxP8VGHtE+Ez5MxYg8hPqvbRfUOzcRxFioX64P/oVe16+sCtQ+OrGYdbNP4v5nFRCI8+JyUwyhDgOlQU95Nszg5R0t56wk+PB8McuHXLJfc5dCnnKP6Z3SlZ3+otwDw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=cryIU+Y4; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="cryIU+Y4" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3B1861F000E9; Wed, 20 May 2026 13:48:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1779284926; bh=aumXBrLrxxQFmyzkYmXrDbHFCke8TkoH++Nv66XdtSY=; h=From:To:Subject:Date; b=cryIU+Y4SMQ9BDgSuvTAmy0n2kIsz1lB3M5yrQ5jiOMj+aVUAkKbf+7fkl6OfNhQk 5dxIhleIBQTI+QCbMiXSGp1pUZ6lqcRBvcJBWgsvCjRDQBJjANUWCJJ1hn0rN5dlCd lGSVi4vzAKQHW4mhPtPT6gvc5kMLc2jIz2MK4bv5O11xzLeSzhyKsZUE/74epR57bq WmAy0m9amqUEHnnGjL+7SJARKJLk5jEqZEAH6k4WI2bYsv+M3Sd4b5Hk+Fhe0jFcoA it6S0qGpiv6/xp5UkHikCKh1gnnYG4Ov58G/HftILvfUI3JYdiGiPLu+LDHKPfL0Fx 0FqepdA7HfjYw== From: Lee Jones To: lee@kernel.org, James Chapman , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH 1/1] l2tp: pppol2tp: hold reference to session in pppol2tp_ioctl() Date: Wed, 20 May 2026 14:48:36 +0100 Message-ID: <20260520134837.2780050-1-lee@kernel.org> X-Mailer: git-send-email 2.54.0.631.ge1b05301d1-goog Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit pppol2tp_ioctl() read sock->sk->sk_user_data directly without any locks or reference counting. If a controllable sleep was induced during copy_from_user() (e.g. via a userfaultfd page fault sleep), a concurrent socket close could trigger pppol2tp_session_close() asynchronously. This frees the l2tp_session structure via the l2tp_session_del_work workqueue. Upon resuming, the ioctl thread dereferences the stale session pointer, resulting in a Use-After-Free (UAF). Fix this by securely fetching the session reference using the RCU-safe, refcounted helper pppol2tp_sock_to_session(sk) on entry. This locks the session's refcount across the sleep. We structured the function to exit via standard err breaks, guaranteeing that l2tp_session_put() is cleanly called on all return paths to drop the reference. Signed-off-by: Lee Jones --- net/l2tp/l2tp_ppp.c | 72 ++++++++++++++++++++++----------------------- 1 file changed, 35 insertions(+), 37 deletions(-) diff --git a/net/l2tp/l2tp_ppp.c b/net/l2tp/l2tp_ppp.c index 99d6582f41de..9a2243a32ceb 100644 --- a/net/l2tp/l2tp_ppp.c +++ b/net/l2tp/l2tp_ppp.c @@ -1045,64 +1045,57 @@ static int pppol2tp_ioctl(struct socket *sock, unsigned int cmd, { struct pppol2tp_ioc_stats stats; struct l2tp_session *session; + int err = 0; + + session = pppol2tp_sock_to_session(sock->sk); + if (!session) + return -ENOTCONN; switch (cmd) { case PPPIOCGMRU: case PPPIOCGFLAGS: - session = sock->sk->sk_user_data; - if (!session) - return -ENOTCONN; - - if (WARN_ON(session->magic != L2TP_SESSION_MAGIC)) - return -EBADF; - /* Not defined for tunnels */ - if (!session->session_id && !session->peer_session_id) - return -ENOSYS; + if (!session->session_id && !session->peer_session_id) { + err = -ENOSYS; + break; + } - if (put_user(0, (int __user *)arg)) - return -EFAULT; + if (put_user(0, (int __user *)arg)) { + err = -EFAULT; + break; + } break; case PPPIOCSMRU: case PPPIOCSFLAGS: - session = sock->sk->sk_user_data; - if (!session) - return -ENOTCONN; - - if (WARN_ON(session->magic != L2TP_SESSION_MAGIC)) - return -EBADF; - /* Not defined for tunnels */ - if (!session->session_id && !session->peer_session_id) - return -ENOSYS; + if (!session->session_id && !session->peer_session_id) { + err = -ENOSYS; + break; + } - if (!access_ok((int __user *)arg, sizeof(int))) - return -EFAULT; + if (!access_ok((int __user *)arg, sizeof(int))) { + err = -EFAULT; + break; + } break; case PPPIOCGL2TPSTATS: - session = sock->sk->sk_user_data; - if (!session) - return -ENOTCONN; - - if (WARN_ON(session->magic != L2TP_SESSION_MAGIC)) - return -EBADF; - /* Session 0 represents the parent tunnel */ if (!session->session_id && !session->peer_session_id) { u32 session_id; - int err; if (copy_from_user(&stats, (void __user *)arg, - sizeof(stats))) - return -EFAULT; + sizeof(stats))) { + err = -EFAULT; + break; + } session_id = stats.session_id; err = pppol2tp_tunnel_copy_stats(&stats, session->tunnel); if (err < 0) - return err; + break; stats.session_id = session_id; } else { @@ -1112,15 +1105,20 @@ static int pppol2tp_ioctl(struct socket *sock, unsigned int cmd, stats.tunnel_id = session->tunnel->tunnel_id; stats.using_ipsec = l2tp_tunnel_uses_xfrm(session->tunnel); - if (copy_to_user((void __user *)arg, &stats, sizeof(stats))) - return -EFAULT; + if (copy_to_user((void __user *)arg, &stats, sizeof(stats))) { + err = -EFAULT; + break; + } break; default: - return -ENOIOCTLCMD; + err = -ENOIOCTLCMD; + break; } - return 0; + l2tp_session_put(session); + + return err; } /***************************************************************************** -- 2.54.0.631.ge1b05301d1-goog