linux-kernel - Re: [PATCH] net: core: scm: fix information leak to userland

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Date:	Sat, 30 Oct 2010 18:50:42 +0400
From:	Vasiliy Kulikov <segooon@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	kernel-janitors@...r.kernel.org,
	"David S. Miller" <davem@...emloft.net>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Tejun Heo <tj@...nel.org>,
	"Serge E. Hallyn" <serge@...lyn.com>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: core: scm: fix information leak to userland

On Sat, Oct 30, 2010 at 16:33 +0200, Eric Dumazet wrote:
> Le samedi 30 octobre 2010 à 18:26 +0400, Vasiliy Kulikov a écrit :
> > Structure cmsghdr is copied to userland with padding bytes
> > unitialized on architectures where __kernel_size_t is unsigned long.
> > It leads to leaking of contents of kernel stack memory.
> > 
> > Signed-off-by: Vasiliy Kulikov <segooon@...il.com>
> > ---
> >  Compile tested.
> > 
> >  net/core/scm.c |    1 +
> >  1 files changed, 1 insertions(+), 0 deletions(-)
> > 
> > diff --git a/net/core/scm.c b/net/core/scm.c
> > index 413cab8..a4a9b70 100644
> > --- a/net/core/scm.c
> > +++ b/net/core/scm.c
> > @@ -233,6 +233,7 @@ int put_cmsg(struct msghdr * msg, int level, int type, int len, void *data)
> >  		msg->msg_flags |= MSG_CTRUNC;
> >  		cmlen = msg->msg_controllen;
> >  	}
> > +	memset(&cmhdr, 0, sizeof(cmhdr));
> >  	cmhdr.cmsg_level = level;
> >  	cmhdr.cmsg_type = type;
> >  	cmhdr.cmsg_len = cmlen;
> 
> 
> ???
> 
> struct cmsghdr {
>         __kernel_size_t cmsg_len;       /* data byte count, including hdr */
>         int             cmsg_level;     /* originating protocol */
>         int             cmsg_type;      /* protocol-specific type */
> };
> 
> Could you explain where are the padding bytes ?

Ah, sorry, nowhere :)  int is stored quite OK after long.  Please ignore this patch.

Thanks,

-- 
Vasiliy
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