From: Jason Gunthorpe <jgg@ziepe.ca>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Leon Romanovsky <leon@kernel.org>,
Peilin Ye <yepeilin.cs@gmail.com>,
Santosh Shilimkar <santosh.shilimkar@oracle.com>,
"David S. Miller" <davem@davemloft.net>,
Jakub Kicinski <kuba@kernel.org>,
Dan Carpenter <dan.carpenter@oracle.com>,
Arnd Bergmann <arnd@arndb.de>,
linux-kernel-mentees@lists.linuxfoundation.org,
netdev@vger.kernel.org, linux-rdma@vger.kernel.org,
rds-devel@oss.oracle.com, linux-kernel@vger.kernel.org
Subject: Re: [Linux-kernel-mentees] [PATCH net] rds: Prevent kernel-infoleak in rds_notify_queue_get()
Date: Fri, 31 Jul 2020 11:04:52 -0300 [thread overview]
Message-ID: <20200731140452.GE24045@ziepe.ca> (raw)
In-Reply-To: <20200731053333.GB466103@kroah.com>
On Fri, Jul 31, 2020 at 07:33:33AM +0200, Greg Kroah-Hartman wrote:
> 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?
The spec was updated in C11 to require zero'ing padding when doing
partial initialization of aggregates (eg = {})
"""if it is an aggregate, every member is initialized (recursively)
according to these rules, and any padding is initialized to zero
bits;"""
The difference between {0} and the {} extension is only that {}
reliably triggers partial initialization for all kinds of aggregates,
while {0} has a number of edge cases where it can fail to compile.
IIRC gcc has cleared the padding during aggregate initialization for a
long time. Considering we have thousands of aggregate initializers it
seems likely to me Linux also requires a compiler with this C11
behavior to operate correctly.
Does this patch actually fix anything? My compiler generates identical
assembly code in either case.
Jason
next prev parent reply other threads:[~2020-07-31 14:04 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-30 19:20 [Linux-kernel-mentees] [PATCH net] rds: Prevent kernel-infoleak in rds_notify_queue_get() Peilin Ye
2020-07-30 19:29 ` santosh.shilimkar
2020-07-31 4:53 ` Leon Romanovsky
2020-07-31 5:33 ` Greg Kroah-Hartman
2020-07-31 5:33 ` Greg Kroah-Hartman
[not found] ` <CAHp75Vdr2HC_ogNhBCxxGut9=Z6pQMFiA0w-268OQv+5unYOTg@mail.gmail.com>
2020-07-31 7:00 ` Leon Romanovsky
2020-07-31 7:05 ` Andy Shevchenko
2020-07-31 14:04 ` Jason Gunthorpe [this message]
2020-07-31 14:21 ` Greg Kroah-Hartman
2020-07-31 14:36 ` Jason Gunthorpe
2020-07-31 17:19 ` Greg Kroah-Hartman
2020-07-31 18:27 ` Jason Gunthorpe
2020-08-01 8:00 ` Dan Carpenter
2020-08-01 14:40 ` Jason Gunthorpe
2020-08-03 9:34 ` Dan Carpenter
2020-08-01 5:38 ` Leon Romanovsky
2020-08-02 22:10 ` Jason Gunthorpe
2020-08-02 22:23 ` Joe Perches
2020-08-02 22:28 ` Jason Gunthorpe
2020-08-02 22:45 ` Joe Perches
2020-08-03 4:58 ` Leon Romanovsky
2020-08-03 23:06 ` Jason Gunthorpe
2020-08-08 22:57 ` Jack Leadford
2020-08-09 7:04 ` Leon Romanovsky
2020-08-14 17:07 ` Jason Gunthorpe
2020-07-31 9:59 ` Dan Carpenter
2020-07-31 11:14 ` Håkon Bugge
2020-07-31 11:59 ` Greg Kroah-Hartman
2020-07-31 12:03 ` Håkon Bugge
2020-07-31 23:54 ` David Miller
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