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Date:   Mon, 7 May 2018 09:42:31 +0800
From:   YU Bo <tsu.yubo@gmail.com>
To:     Wenwen Wang <wang6495@umn.edu>
Cc:     Kangjie Lu <kjlu@umn.edu>, Armin Schindler <mac@melware.de>,
        Karsten Keil <isdn@linux-pingi.de>,
        "open list:ISDN SUBSYSTEM" <netdev@vger.kernel.org>,
        open list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] isdn: eicon: fix a missing-check bug
Message-ID: <20180507014230.5wquwxjoeztuv2k5@debian.debian>
Mail-Followup-To: Wenwen Wang <wang6495@umn.edu>, Kangjie Lu <kjlu@umn.edu>,
        Armin Schindler <mac@melware.de>,
        Karsten Keil <isdn@linux-pingi.de>,
        "open list:ISDN SUBSYSTEM" <netdev@vger.kernel.org>,
        open list <linux-kernel@vger.kernel.org>
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Hello,
I am just notice your subject line.There are missing something i think
On Sat, May 05, 2018 at 02:32:46PM -0500, Wenwen Wang wrote:
>In divasmain.c, the function divas_write() firstly invokes the function
>diva_xdi_open_adapter() to open the adapter that matches with the adapter
>number provided by the user, and then invokes the function diva_xdi_write()
>to perform the write operation using the matched adapter. The two functions
>diva_xdi_open_adapter() and diva_xdi_write() are located in diva.c.
>
>In diva_xdi_open_adapter(), the user command is copied to the object 'msg'
>from the userspace pointer 'src' through the function pointer 'cp_fn',
>which eventually calls copy_from_user() to do the copy. Then, the adapter
>number 'msg.adapter' is used to find out a matched adapter from the
>'adapter_queue'. A matched adapter will be returned if it is found.
>Otherwise, NULL is returned to indicate the failure of the verification on
>the adapter number.
>
>As mentioned above, if a matched adapter is returned, the function
>diva_xdi_write() is invoked to perform the write operation. In this
>function, the user command is copied once again from the userspace pointer
>'src', which is the same as the 'src' pointer in diva_xdi_open_adapter() as
>both of them are from the 'buf' pointer in divas_write(). Similarly, the
>copy is achieved through the function pointer 'cp_fn', which finally calls
>copy_from_user(). After the successful copy, the corresponding command
>processing handler of the matched adapter is invoked to perform the write
>operation.
>
>It is obvious that there are two copies here from userspace, one is in
>diva_xdi_open_adapter(), and one is in diva_xdi_write(). Plus, both of
>these two copies share the same source userspace pointer, i.e., the 'buf'
>pointer in divas_write(). Given that a malicious userspace process can race
>to change the content pointed by the 'buf' pointer, this can pose potential
>security issues. For example, in the first copy, the user provides a valid
>adapter number to pass the verification process and a valid adapter can be
>found. Then the user can modify the adapter number to an invalid number.
>This way, the user can bypass the verification process of the adapter
>number and inject inconsistent data.
>
>To avoid such issues, this patch adds a check after the second copy in the
>function diva_xdi_write(). If the adapter number is not equal to the one
>obtained in the first copy, (-4) will be returned to divas_write(), which
>will then return an error code -EINVAL.
>
>Signed-off-by: Wenwen Wang <wang6495@umn.edu>
>---
> drivers/isdn/hardware/eicon/diva.c      | 6 +++++-
> drivers/isdn/hardware/eicon/divasmain.c | 3 +++
> 2 files changed, 8 insertions(+), 1 deletion(-)
>
>diff --git a/drivers/isdn/hardware/eicon/diva.c b/drivers/isdn/hardware/eicon/diva.c
>index 944a7f3..46cbf76 100644
>--- a/drivers/isdn/hardware/eicon/diva.c
>+++ b/drivers/isdn/hardware/eicon/diva.c
>@@ -440,6 +440,7 @@ diva_xdi_write(void *adapter, void *os_handle, const void __user *src,
> 	       int length, divas_xdi_copy_from_user_fn_t cp_fn)
> {
> 	diva_os_xdi_adapter_t *a = (diva_os_xdi_adapter_t *) adapter;
>+	diva_xdi_um_cfg_cmd_t *p;
> 	void *data;
>
> 	if (a->xdi_mbox.status & DIVA_XDI_MBOX_BUSY) {
>@@ -461,7 +462,10 @@ diva_xdi_write(void *adapter, void *os_handle, const void __user *src,
>
> 	length = (*cp_fn) (os_handle, data, src, length);
> 	if (length > 0) {
>-		if ((*(a->interface.cmd_proc))
>+		p = (diva_xdi_um_cfg_cmd_t *) data;
>+		if (a->controller != (int)p->adapter) {
>+			length = -4;
>+		} else if ((*(a->interface.cmd_proc))
> 		    (a, (diva_xdi_um_cfg_cmd_t *) data, length)) {
> 			length = -3;
> 		}
>diff --git a/drivers/isdn/hardware/eicon/divasmain.c b/drivers/isdn/hardware/eicon/divasmain.c
>index b9980e8..a03c658 100644
>--- a/drivers/isdn/hardware/eicon/divasmain.c
>+++ b/drivers/isdn/hardware/eicon/divasmain.c
>@@ -614,6 +614,9 @@ static ssize_t divas_write(struct file *file, const char __user *buf,
> 	case -3:
> 		ret = -ENXIO;
> 		break;
>+	case -4:
>+		ret = -EINVAL;
>+		break;
> 	}
> 	DBG_TRC(("write: ret %d", ret));
> 	return (ret);
>--
>2.7.4
>