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

piaojun
2018-08-03T01:46:30Z

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@huawei.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@huawei.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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