linux-kernel - Re: [Xen-devel] [PATCH] [v2] xen: hypercall: fix out-of-bounds memcpy

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Date:   Mon, 5 Feb 2018 16:47:18 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Jan Beulich <JBeulich@...e.com>
Cc:     David Laight <David.Laight@...lab.com>,
        xen-devel <xen-devel@...ts.xenproject.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [Xen-devel] [PATCH] [v2] xen: hypercall: fix out-of-bounds memcpy

On Mon, Feb 5, 2018 at 4:14 PM, Jan Beulich <JBeulich@...e.com> wrote:
>>>> On 05.02.18 at 16:03, <arnd@...db.de> wrote:
>>  int xen_event_channel_op_compat(int cmd, void *arg)
>>  {
>> -     struct evtchn_op op;
>> +     struct evtchn_op op = { .cmd = cmd, };
>> +     size_t len;
>>       int rc;
>>
>> -     op.cmd = cmd;
>> -     memcpy(&op.u, arg, sizeof(op.u));
>> -     rc = _hypercall1(int, event_channel_op_compat, &op);
>> -
>> -     switch (cmd) {
>> -     case EVTCHNOP_close:
>> -     case EVTCHNOP_send:
>> -     case EVTCHNOP_bind_vcpu:
>> -     case EVTCHNOP_unmask:
>> -             /* no output */
>> -             break;
>> +     if (cmd > ARRAY_SIZE(evtchnop_len))
>> +             return -ENOSYS;
>
>>= perhaps?

Argh, of course. This is why I preferred the switch/case version, I knew
I'd screw this up somehow ;-)

       Arnd