linux-kernel - Re: [PATCH 6/8] char: synclink: fix information leak to userland

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Date:	Sun, 17 Oct 2010 19:38:39 +0400
From:	Vasiliy Kulikov <segooon@...il.com>
To:	Jiri Slaby <jslaby@...e.cz>
Cc:	kernel-janitors@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Alan Cox <alan@...ux.intel.com>, Arnd Bergmann <arnd@...db.de>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 6/8] char: synclink: fix information leak to userland

On Sun, Oct 17, 2010 at 17:34 +0200, Jiri Slaby wrote:
> On 10/17/2010 04:41 PM, Vasiliy Kulikov wrote:
> > Structure new_line is copied to userland with some padding fields unitialized.
> > It leads to leaking of stack memory.
> 
> I think your tool has a bug. I must admit I fail to see the padding
> which would cause leaks. Could you elaborate?

I didn't use any tool except "grep copy_to_user" :)

    typedef struct { 
        unsigned int clock_rate; /* bits per second */
        unsigned int clock_type; /* internal, external, TX-internal etc. */
        unsigned short loopback;
    } sync_serial_settings;          /* V.35, V.24, X.21 */

On x86_64 sizeof(sync_serial_settings) = 4 + 4 + 2 + 2 = 12.
The last 2 is padding.

> 
> > Signed-off-by: Vasiliy Kulikov <segooon@...il.com>
> > ---
> >  Compile tested.
> > 
> >  drivers/char/synclink.c |    2 ++
> >  1 files changed, 2 insertions(+), 0 deletions(-)
> > 
> > diff --git a/drivers/char/synclink.c b/drivers/char/synclink.c
> > index 3a6824f..abd0867 100644
> > --- a/drivers/char/synclink.c
> > +++ b/drivers/char/synclink.c
> > @@ -7846,6 +7846,8 @@ static int hdlcdev_ioctl(struct net_device *dev, struct ifreq *ifr, int cmd)
> >  	if (cmd != SIOCWANDEV)
> >  		return hdlc_ioctl(dev, ifr, cmd);
> >  
> > +	memset(&new_line, 0, size);
> > +
> >  	switch(ifr->ifr_settings.type) {
> >  	case IF_GET_IFACE: /* return current sync_serial_settings */
> >  
> 
> 
> -- 
> js
> suse labs

-- 
Vasiliy
--
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