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Subject: Re: [Linux-kernel-mentees] [PATCH net] rds: Prevent kernel-infoleak
 in rds_notify_queue_get()
From:   =?utf-8?Q?H=C3=A5kon_Bugge?= <haakon.bugge@oracle.com>
In-Reply-To: <20200731095943.GI5493@kadam>
Date:   Fri, 31 Jul 2020 13:14:09 +0200
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>,
        Arnd Bergmann <arnd@arndb.de>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-kernel-mentees@lists.linuxfoundation.org,
        netdev@vger.kernel.org,
        OFED mailing list <linux-rdma@vger.kernel.org>,
        rds-devel@oss.oracle.com, linux-kernel@vger.kernel.org
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Message-Id: <81B40AF5-EBCA-4628-8CF6-687C12134552@oracle.com>
References: <20200730192026.110246-1-yepeilin.cs@gmail.com>
 <20200731045301.GI75549@unreal> <20200731095943.GI5493@kadam>
To:     Dan Carpenter <dan.carpenter@oracle.com>
Sender: linux-kernel-owner@vger.kernel.org
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> On 31 Jul 2020, at 11:59, Dan Carpenter <dan.carpenter@oracle.com> =
wrote:
>=20
> 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`.
>>>=20
>>> In 2016 we tried to fix this issue by doing `=3D { 0 };` on `cmsg`, =
which
>>> unfortunately does not always initialize that 4-byte hole. Fix it by =
using
>>> memset() instead.
>>=20
>> Of course, this is the difference between "{ 0 }" and "{}" =
initializations.
>>=20
>=20
> No, there is no difference.  Even struct assignments like:
>=20
> 	foo =3D *bar;
>=20
> 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, H=C3=A5kon


> regards,
> dan carpenter
>=20