linux-kernel - Re: [PATCH for 5.10] vdpa_sim: fix param validation in vdpasim_get

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Message-ID: <20210215150321.anwcogkifg6sefp6@steredhat>
Date:   Mon, 15 Feb 2021 16:03:21 +0100
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     stable@...r.kernel.org, Jason Wang <jasowang@...hat.com>,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, Eli Cohen <elic@...dia.com>,
        "Michael S. Tsirkin" <mst@...hat.com>
Subject: Re: [PATCH for 5.10] vdpa_sim: fix param validation in
 vdpasim_get_config()

On Mon, Feb 15, 2021 at 03:32:19PM +0100, Greg KH wrote:
>On Thu, Feb 11, 2021 at 05:25:19PM +0100, Stefano Garzarella wrote:
>> Commit 65b709586e222fa6ffd4166ac7fdb5d5dad113ee upstream.
>
>No, this really is not that commit, so please do not say it is.

Oops, sorry.

>
>> Before this patch, if 'offset + len' was equal to
>> sizeof(struct virtio_net_config), the entire buffer wasn't filled,
>> returning incorrect values to the caller.
>>
>> Since 'vdpasim->config' type is 'struct virtio_net_config', we can
>> safely copy its content under this condition.
>>
>> Commit 65b709586e22 ("vdpa_sim: add get_config callback in
>> vdpasim_dev_attr") unintentionally solved it upstream while
>> refactoring vdpa_sim.c to support multiple devices. But we don't want
>> to backport it to stable branches as it contains many changes.
>>
>> Fixes: 2c53d0f64c06 ("vdpasim: vDPA device simulator")
>> Cc: <stable@...r.kernel.org> # 5.10.x
>> Signed-off-by: Stefano Garzarella <sgarzare@...hat.com>
>> ---
>>  drivers/vdpa/vdpa_sim/vdpa_sim.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim.c b/drivers/vdpa/vdpa_sim/vdpa_sim.c
>> index 6a90fdb9cbfc..8ca178d7b02f 100644
>> --- a/drivers/vdpa/vdpa_sim/vdpa_sim.c
>> +++ b/drivers/vdpa/vdpa_sim/vdpa_sim.c
>> @@ -572,7 +572,7 @@ static void vdpasim_get_config(struct vdpa_device *vdpa, unsigned int offset,
>>  {
>>  	struct vdpasim *vdpasim = vdpa_to_sim(vdpa);
>>
>> -	if (offset + len < sizeof(struct virtio_net_config))
>> +	if (offset + len <= sizeof(struct virtio_net_config))
>>  		memcpy(buf, (u8 *)&vdpasim->config + offset, len);
>>  }
>
>I'll be glad to take a one-off patch, but why can't we take the real
>upstream patch?  That is always the better long-term solution, right?

Because that patch depends on the following patches merged in v5.11-rc1 
while refactoring vdpa_sim:
   f37cbbc65178 vdpa_sim: make 'config' generic and usable for any device type
   cf1a3b35382c vdpa_sim: store parsed MAC address in a buffer
   a13b5918fdd0 vdpa_sim: add work_fn in vdpasim_dev_attr
   011c35bac5ef vdpa_sim: add supported_features field in vdpasim_dev_attr
   2f8f46188805 vdpa_sim: add device id field in vdpasim_dev_attr
   6c6e28fe4579 vdpa_sim: add struct vdpasim_dev_attr for device attributes
   36a9c3063025 vdpa_sim: rename vdpasim_config_ops variables
   423248d60d2b vdpa_sim: remove hard-coded virtq count

Maybe we can skip some of them, but IMHO should be less risky to apply 
only this change.

If you want I can try to figure out the minimum sub-set of patches 
needed for 65b709586e22 ("vdpa_sim: add get_config callback in 
vdpasim_dev_attr").

Thanks,
Stefano