linux-kernel - Re: [Linux-kernel-mentees] [PATCH net] rds: Prevent kernel-infoleak in rds_notify_queue

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Message-ID: <20200731053333.GB466103@kroah.com>
Date:   Fri, 31 Jul 2020 07:33:33 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Leon Romanovsky <leon@...nel.org>
Cc:     Peilin Ye <yepeilin.cs@...il.com>,
        Santosh Shilimkar <santosh.shilimkar@...cle.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Arnd Bergmann <arnd@...db.de>,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        netdev@...r.kernel.org, linux-rdma@...r.kernel.org,
        rds-devel@....oracle.com, linux-kernel@...r.kernel.org
Subject: Re: [Linux-kernel-mentees] [PATCH net] rds: Prevent kernel-infoleak
 in rds_notify_queue_get()

On Fri, Jul 31, 2020 at 07:33:06AM +0200, Greg Kroah-Hartman wrote:
> On Fri, Jul 31, 2020 at 07:53:01AM +0300, Leon Romanovsky wrote:
> > On Thu, Jul 30, 2020 at 03:20:26PM -0400, Peilin Ye wrote:
> > > rds_notify_queue_get() is potentially copying uninitialized kernel stack
> > > memory to userspace since the compiler may leave a 4-byte hole at the end
> > > of `cmsg`.
> > >
> > > In 2016 we tried to fix this issue by doing `= { 0 };` on `cmsg`, which
> > > unfortunately does not always initialize that 4-byte hole. Fix it by using
> > > memset() instead.
> > 
> > Of course, this is the difference between "{ 0 }" and "{}" initializations.
> 
> Really?  Neither will handle structures with holes in it, try it and
> see.

And if true, where in the C spec does it say that?

thanks,

greg k-h