linux-kernel - Re: [V9fs-developer] [PATCH v2] net/9p/trans_virtio.c: add null terminal for mount tag

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Date:   Fri, 3 Aug 2018 09:45:50 +0800
From:   piaojun <piaojun@...wei.com>
To:     Greg Kurz <groug@...d.org>
CC:     Dominique Martinet <asmadeus@...ewreck.org>,
        Latchesar Ionkov <lucho@...kov.net>,
        Eric Van Hensbergen <ericvh@...il.com>,
        "Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
        <v9fs-developer@...ts.sourceforge.net>,
        Ron Minnich <rminnich@...dia.gov>
Subject: Re: [V9fs-developer] [PATCH v2] net/9p/trans_virtio.c: add null
 terminal for mount tag

Hi Greg and Dominique,

We'd better reach an agreement about the patch fix. In my opinion,
replacing strlen(chan->tag) with a local variable sounds reasonable, and
changing strncmp to strcmp may be little beneficial, as strcmp is more
dangerours such as buffer-flow. So I'd like to hear your suggestion for
the next version of the patch, or this patch is good enough?

Thanks,
Jun

On 2018/8/2 21:23, Greg Kurz wrote:
> On Thu, 2 Aug 2018 09:59:38 +0800
> piaojun <piaojun@...wei.com> wrote:
> 
>> Hi Dominique,
>>
>> On 2018/8/2 9:54, Dominique Martinet wrote:
>>> piaojun wrote on Thu, Aug 02, 2018:  
>>>> chan->tag is Non-null terminated which will result in printing messy code
>>>> when debugging code. So we should add '\0' for tag to make the code more
>>>> convenient and robust. In addition, I drop char->tag_len to simplify the
>>>> code.  
>>>
>>> Some new lines in commit message would be appreciated.
>>>
>>> That aside, I have a couple of nitpicks, but it looks good to me - thanks
>>>   
>>>>
>>>> Signed-off-by: Jun Piao <piaojun@...wei.com>
>>>> ---
>>>>  net/9p/trans_virtio.c | 15 +++++----------
>>>>  1 file changed, 5 insertions(+), 10 deletions(-)
>>>>
>>>> diff --git a/net/9p/trans_virtio.c b/net/9p/trans_virtio.c
>>>> index d422bfc..0fe9c37 100644
>>>> --- a/net/9p/trans_virtio.c
>>>> +++ b/net/9p/trans_virtio.c
>>>> @@ -89,10 +89,8 @@ struct virtio_chan {
>>>>  	unsigned long p9_max_pages;
>>>>  	/* Scatterlist: can be too big for stack. */
>>>>  	struct scatterlist sg[VIRTQUEUE_NUM];
>>>> -
>>>> -	int tag_len;
>>>>  	/*
>>>> -	 * tag name to identify a mount Non-null terminated
>>>> +	 * tag name to identify a mount null terminated
>>>>  	 */
>>>>  	char *tag;
>>>>
>>>> @@ -529,10 +527,9 @@ static ssize_t p9_mount_tag_show(struct device *dev,
>>>>  	vdev = dev_to_virtio(dev);
>>>>  	chan = vdev->priv;
>>>>
>>>> -	memcpy(buf, chan->tag, chan->tag_len);
>>>> -	buf[chan->tag_len] = 0;
>>>> +	memcpy(buf, chan->tag, strlen(chan->tag) + 1);
>>>>
>>>> -	return chan->tag_len + 1;
>>>> +	return strlen(chan->tag) + 1;  
>>>
>>> Use a local variable for strlen(chan->tag)?
>>>   
>> Yes, local variable looks better.
>>
>>>>  }
>>>>
>>>>  static DEVICE_ATTR(mount_tag, 0444, p9_mount_tag_show, NULL);
>>>> @@ -585,7 +582,7 @@ static int p9_virtio_probe(struct virtio_device *vdev)
>>>>  		err = -EINVAL;
>>>>  		goto out_free_vq;
>>>>  	}
>>>> -	tag = kmalloc(tag_len, GFP_KERNEL);
>>>> +	tag = kzalloc(tag_len + 1, GFP_KERNEL);
>>>>  	if (!tag) {
>>>>  		err = -ENOMEM;
>>>>  		goto out_free_vq;
>>>> @@ -594,7 +591,6 @@ static int p9_virtio_probe(struct virtio_device *vdev)
>>>>  	virtio_cread_bytes(vdev, offsetof(struct virtio_9p_config, tag),
>>>>  			   tag, tag_len);
>>>>  	chan->tag = tag;
>>>> -	chan->tag_len = tag_len;
>>>>  	err = sysfs_create_file(&(vdev->dev.kobj), &dev_attr_mount_tag.attr);
>>>>  	if (err) {
>>>>  		goto out_free_tag;
>>>> @@ -654,8 +650,7 @@ static int p9_virtio_probe(struct virtio_device *vdev)
>>>>
>>>>  	mutex_lock(&virtio_9p_lock);
>>>>  	list_for_each_entry(chan, &virtio_chan_list, chan_list) {
>>>> -		if (!strncmp(devname, chan->tag, chan->tag_len) &&
>>>> -		    strlen(devname) == chan->tag_len) {
>>>> +		if (!strncmp(devname, chan->tag, strlen(chan->tag) + 1)) {  
>>>
>>> strncmp(x, y, strlen(y)+1) is precisely what strcmp does so let's use
>>> the simpler version
>>>   
>> strcmp looks simpler, and I will wait for a while to hear more
>> suggestions, and then post another patch for these fixes.
>>
> 
> Nothing more to add. Please go ahead.
> 
>> Thanks,
>> Jun
>>
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> 
> .
>