[PATCH] drivers/video/via/ioctl.c: prevent reading uninitialized

[PATCH] drivers/video/via/ioctl.c: prevent reading uninitialized

[Dan Rosenberg]

The VIAFB_GET_INFO device ioctl allows unprivileged users to read 1968
bytes of uninitialized stack memory, because the "reserved" member of
the viafb_ioctl_info struct declared on the stack is not altered or
zeroed before being copied back to the user.  This patch takes care of
it.

Signed-off-by: Dan Rosenberg <dan.j.rosenberg@gmail.com>

--- linux-2.6.35.4.orig/drivers/video/via/ioctl.c	2010-08-26 19:47:12.000000000 -0400
+++ linux-2.6.35.4/drivers/video/via/ioctl.c	2010-09-15 11:53:29.997375748 -0400
@@ -25,6 +25,8 @@ int viafb_ioctl_get_viafb_info(u_long ar
 {
 	struct viafb_ioctl_info viainfo;
 
+	memset(&viainfo, 0, sizeof(struct viafb_ioctl));
+
 	viainfo.viafb_id = VIAID;
 	viainfo.vendor_id = PCI_VIA_VENDOR_ID;
 

Re: [PATCH] drivers/video/via/ioctl.c: prevent reading uninitialized

[Florian Tobias Schandinat]

Hi,

Dan Rosenberg schrieb:
> The VIAFB_GET_INFO device ioctl allows unprivileged users to read 1968
> bytes of uninitialized stack memory, because the "reserved" member of
> the viafb_ioctl_info struct declared on the stack is not altered or
> zeroed before being copied back to the user.  This patch takes care of
> it.

I am wondering about the number of bytes as sizeof(struct viafb_ioctl_info) = 
256 so it should be a bit less. But that's just nitpicking, the issue is 
certainly real. Your patch does the right thing but there is a bug in it:

> Signed-off-by: Dan Rosenberg <dan.j.rosenberg@gmail.com>
> 
> --- linux-2.6.35.4.orig/drivers/video/via/ioctl.c	2010-08-26 19:47:12.000000000 -0400
> +++ linux-2.6.35.4/drivers/video/via/ioctl.c	2010-09-15 11:53:29.997375748 -0400
> @@ -25,6 +25,8 @@ int viafb_ioctl_get_viafb_info(u_long ar
>  {
>  	struct viafb_ioctl_info viainfo;
>  
> +	memset(&viainfo, 0, sizeof(struct viafb_ioctl));

Shouldn't it be sizeof(struct viafb_ioctl_info) or sizeof(viainfo) ?
At least here it does not even compile otherwise....


Thanks,

Florian Tobias Schandinat

Re: [PATCH] drivers/video/via/ioctl.c: prevent reading

[Steven Rostedt]

On Wed, Sep 15, 2010 at 05:44:19PM -0400, Dan Rosenberg wrote:
> The VIAFB_GET_INFO device ioctl allows unprivileged users to read 1968
> bytes of uninitialized stack memory, because the "reserved" member of
> the viafb_ioctl_info struct declared on the stack is not altered or
> zeroed before being copied back to the user.  This patch takes care of
> it.
> 
> Signed-off-by: Dan Rosenberg <dan.j.rosenberg@gmail.com>
> 
> --- linux-2.6.35.4.orig/drivers/video/via/ioctl.c	2010-08-26 19:47:12.000000000 -0400
> +++ linux-2.6.35.4/drivers/video/via/ioctl.c	2010-09-15 11:53:29.997375748 -0400
> @@ -25,6 +25,8 @@ int viafb_ioctl_get_viafb_info(u_long ar
>  {
>  	struct viafb_ioctl_info viainfo;
>  
> +	memset(&viainfo, 0, sizeof(struct viafb_ioctl));
> +

Again, this could probably be better off as:

-  	struct viafb_ioctl_info viainfo;
+  	struct viafb_ioctl_info viainfo = {
+  		.viafb_id = VIAID,
+ 		.vendor_id = PCI_VIA_VENDOR_ID,
+	};

-  	viainfo.viafb_id = VIAID;
-  	viainfo.vendor_id = PCI_VIA_VENDOR_ID;

-- Steve

>  	viainfo.viafb_id = VIAID;
>  	viainfo.vendor_id = PCI_VIA_VENDOR_ID;
>  
> 
> 
> 
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