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[23.128.96.18]) by mx.google.com with ESMTP id f19si4055621edu.388.2021.06.14.04.01.28; Mon, 14 Jun 2021 04:01:50 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18; Authentication-Results: mx.google.com; dkim=pass header.i=@linuxfoundation.org header.s=korg header.b="gek5h/2s"; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=linuxfoundation.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234969AbhFNK7t (ORCPT + 99 others); Mon, 14 Jun 2021 06:59:49 -0400 Received: from mail.kernel.org ([198.145.29.99]:52688 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234050AbhFNKvH (ORCPT ); Mon, 14 Jun 2021 06:51:07 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 603FC61464; Mon, 14 Jun 2021 10:38:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1623667133; bh=D6ZED7p3zja0m7Hj1BJucKeJYgz7zyrlAByLjarxpyk=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=gek5h/2sNfwq9cQhWclcygp2oC/eMm74rVqBbV5eWZhUR5qudsDw7Oe/HMdr97N4M YYM4MT91obLcAkR84dZw9lXzAgSJlfzPM6679loelCG82jADTKlCjnT+kZJH5iz3tE hQOIFMzHEsbXEGOtdweIRSx9zi0DKe/8yr1vYoOQ= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Dan Carpenter , Desmond Cheong Zhi Xi , Daniel Vetter Subject: [PATCH 5.4 40/84] drm: Lock pointer access in drm_master_release() Date: Mon, 14 Jun 2021 12:27:18 +0200 Message-Id: <20210614102647.732502686@linuxfoundation.org> X-Mailer: git-send-email 2.32.0 In-Reply-To: <20210614102646.341387537@linuxfoundation.org> References: <20210614102646.341387537@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Desmond Cheong Zhi Xi commit c336a5ee984708db4826ef9e47d184e638e29717 upstream. This patch eliminates the following smatch warning: drivers/gpu/drm/drm_auth.c:320 drm_master_release() warn: unlocked access 'master' (line 318) expected lock '&dev->master_mutex' The 'file_priv->master' field should be protected by the mutex lock to '&dev->master_mutex'. This is because other processes can concurrently modify this field and free the current 'file_priv->master' pointer. This could result in a use-after-free error when 'master' is dereferenced in subsequent function calls to 'drm_legacy_lock_master_cleanup()' or to 'drm_lease_revoke()'. An example of a scenario that would produce this error can be seen from a similar bug in 'drm_getunique()' that was reported by Syzbot: https://syzkaller.appspot.com/bug?id=148d2f1dfac64af52ffd27b661981a540724f803 In the Syzbot report, another process concurrently acquired the device's master mutex in 'drm_setmaster_ioctl()', then overwrote 'fpriv->master' in 'drm_new_set_master()'. The old value of 'fpriv->master' was subsequently freed before the mutex was unlocked. Reported-by: Dan Carpenter Signed-off-by: Desmond Cheong Zhi Xi Cc: stable@vger.kernel.org Signed-off-by: Daniel Vetter Link: https://patchwork.freedesktop.org/patch/msgid/20210609092119.173590-1-desmondcheongzx@gmail.com Signed-off-by: Greg Kroah-Hartman --- drivers/gpu/drm/drm_auth.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) --- a/drivers/gpu/drm/drm_auth.c +++ b/drivers/gpu/drm/drm_auth.c @@ -268,9 +268,10 @@ int drm_master_open(struct drm_file *fil void drm_master_release(struct drm_file *file_priv) { struct drm_device *dev = file_priv->minor->dev; - struct drm_master *master = file_priv->master; + struct drm_master *master; mutex_lock(&dev->master_mutex); + master = file_priv->master; if (file_priv->magic) idr_remove(&file_priv->master->magic_map, file_priv->magic);