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

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Message-Id: <81B40AF5-EBCA-4628-8CF6-687C12134552@oracle.com>
Date:   Fri, 31 Jul 2020 13:14:09 +0200
From:   Håkon Bugge <haakon.bugge@...cle.com>
To:     Dan Carpenter <dan.carpenter@...cle.com>
Cc:     Leon Romanovsky <leon@...nel.org>,
        Peilin Ye <yepeilin.cs@...il.com>,
        Santosh Shilimkar <santosh.shilimkar@...cle.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        netdev@...r.kernel.org,
        OFED mailing list <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 31 Jul 2020, at 11:59, Dan Carpenter <dan.carpenter@...cle.com> 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.
>> 
> 
> No, there is no difference.  Even struct assignments like:
> 
> 	foo = *bar;
> 
> can leave struct holes uninitialized.  Depending on the compiler the
> assignment can be implemented as a memset() or as a series of struct
> member assignments.

What about:

struct rds_rdma_notify {
	__u64                      user_token;
	__s32                      status;
} __attribute__((packed));


Thxs, Håkon


> regards,
> dan carpenter
>