From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9AD85C3279B for ; Tue, 10 Jul 2018 18:27:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6840520936 for ; Tue, 10 Jul 2018 18:27:24 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6840520936 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linuxfoundation.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1733114AbeGJS1b (ORCPT ); Tue, 10 Jul 2018 14:27:31 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:44806 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732400AbeGJS1b (ORCPT ); Tue, 10 Jul 2018 14:27:31 -0400 Received: from localhost (LFbn-1-12247-202.w90-92.abo.wanadoo.fr [90.92.61.202]) by mail.linuxfoundation.org (Postfix) with ESMTPSA id 4118DD66; Tue, 10 Jul 2018 18:27:20 +0000 (UTC) From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Jann Horn , Douglas Gilbert , "Martin K. Petersen" Subject: [PATCH 4.4 18/47] scsi: sg: mitigate read/write abuse Date: Tue, 10 Jul 2018 20:24:42 +0200 Message-Id: <20180710182337.902591750@linuxfoundation.org> X-Mailer: git-send-email 2.18.0 In-Reply-To: <20180710182337.047502999@linuxfoundation.org> References: <20180710182337.047502999@linuxfoundation.org> User-Agent: quilt/0.65 X-stable: review MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 4.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Jann Horn commit 26b5b874aff5659a7e26e5b1997e3df2c41fa7fd upstream. As Al Viro noted in commit 128394eff343 ("sg_write()/bsg_write() is not fit to be called under KERNEL_DS"), sg improperly accesses userspace memory outside the provided buffer, permitting kernel memory corruption via splice(). But it doesn't just do it on ->write(), also on ->read(). As a band-aid, make sure that the ->read() and ->write() handlers can not be called in weird contexts (kernel context or credentials different from file opener), like for ib_safe_file_access(). If someone needs to use these interfaces from different security contexts, a new interface should be written that goes through the ->ioctl() handler. I've mostly copypasted ib_safe_file_access() over as sg_safe_file_access() because I couldn't find a good common header - please tell me if you know a better way. [mkp: s/_safe_/_check_/] Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Cc: Signed-off-by: Jann Horn Acked-by: Douglas Gilbert Signed-off-by: Martin K. Petersen Signed-off-by: Greg Kroah-Hartman --- drivers/scsi/sg.c | 42 ++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 40 insertions(+), 2 deletions(-) --- a/drivers/scsi/sg.c +++ b/drivers/scsi/sg.c @@ -51,6 +51,7 @@ static int sg_version_num = 30536; /* 2 #include #include #include +#include /* for sg_check_file_access() */ #include "scsi.h" #include @@ -221,6 +222,33 @@ static void sg_device_destroy(struct kre sdev_prefix_printk(prefix, (sdp)->device, \ (sdp)->disk->disk_name, fmt, ##a) +/* + * The SCSI interfaces that use read() and write() as an asynchronous variant of + * ioctl(..., SG_IO, ...) are fundamentally unsafe, since there are lots of ways + * to trigger read() and write() calls from various contexts with elevated + * privileges. This can lead to kernel memory corruption (e.g. if these + * interfaces are called through splice()) and privilege escalation inside + * userspace (e.g. if a process with access to such a device passes a file + * descriptor to a SUID binary as stdin/stdout/stderr). + * + * This function provides protection for the legacy API by restricting the + * calling context. + */ +static int sg_check_file_access(struct file *filp, const char *caller) +{ + if (filp->f_cred != current_real_cred()) { + pr_err_once("%s: process %d (%s) changed security contexts after opening file descriptor, this is not allowed.\n", + caller, task_tgid_vnr(current), current->comm); + return -EPERM; + } + if (unlikely(segment_eq(get_fs(), KERNEL_DS))) { + pr_err_once("%s: process %d (%s) called from kernel context, this is not allowed.\n", + caller, task_tgid_vnr(current), current->comm); + return -EACCES; + } + return 0; +} + static int sg_allow_access(struct file *filp, unsigned char *cmd) { struct sg_fd *sfp = filp->private_data; @@ -405,6 +433,14 @@ sg_read(struct file *filp, char __user * struct sg_header *old_hdr = NULL; int retval = 0; + /* + * This could cause a response to be stranded. Close the associated + * file descriptor to free up any resources being held. + */ + retval = sg_check_file_access(filp, __func__); + if (retval) + return retval; + if ((!(sfp = (Sg_fd *) filp->private_data)) || (!(sdp = sfp->parentdp))) return -ENXIO; SCSI_LOG_TIMEOUT(3, sg_printk(KERN_INFO, sdp, @@ -592,9 +628,11 @@ sg_write(struct file *filp, const char _ struct sg_header old_hdr; sg_io_hdr_t *hp; unsigned char cmnd[SG_MAX_CDB_SIZE]; + int retval; - if (unlikely(segment_eq(get_fs(), KERNEL_DS))) - return -EINVAL; + retval = sg_check_file_access(filp, __func__); + if (retval) + return retval; if ((!(sfp = (Sg_fd *) filp->private_data)) || (!(sdp = sfp->parentdp))) return -ENXIO;