linux-kernel - Re: [PATCH] vduse: Fix a possible warning in vduse_create

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Date:   Sun, 27 Nov 2022 08:16:24 +0530
From:   Harshit Mogalapalli <harshit.m.mogalapalli@...cle.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     error27@...il.com, harshit.m.mogalapalli@...il.com,
        Jason Wang <jasowang@...hat.com>,
        Xie Yongji <xieyongji@...edance.com>,
        Gautam Dawar <gautam.dawar@...inx.com>,
        Maxime Coquelin <maxime.coquelin@...hat.com>,
        Guanjun <guanjun@...ux.alibaba.com>,
        Parav Pandit <parav@...dia.com>, Eli Cohen <elic@...dia.com>,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org,
        Harshit Mogalapalli <harshit.m.mogalapalli@...cle.com>
Subject: Re: [PATCH] vduse: Fix a possible warning in vduse_create_dev()

Hi Micheal,

On 27/11/22 4:52 am, Michael S. Tsirkin wrote:
> On Fri, Nov 25, 2022 at 07:59:58PM -0800, Harshit Mogalapalli wrote:
>> As 'dev->vq_num' is user-controlled data, if user tries to allocate
>> memory larger than(>=) MAX_ORDER, then kcalloc() will fail, it
>> creates a stack trace and messes up dmesg with a warning.
>>
>> Call trace:
>> -> vduse_ioctl
>> --> vduse_create_dev
>> 'config->vq_num' is user data as it comes from ioctl, which is
>> assigned to 'dev->vq_num'.
>>
>> Add __GFP_NOWARN in order to avoid too large allocation warning.
>> This is detected by static analysis using smatch.
>>
>> Fixes: c8a6153b6c59 ("vduse: Introduce VDUSE - vDPA Device in Userspace")
>> Signed-off-by: Harshit Mogalapalli <harshit.m.mogalapalli@...cle.com>
>> ---
>>   drivers/vdpa/vdpa_user/vduse_dev.c | 3 ++-
>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/vdpa/vdpa_user/vduse_dev.c b/drivers/vdpa/vdpa_user/vduse_dev.c
>> index 35dceee3ed56..5e9546b16165 100644
>> --- a/drivers/vdpa/vdpa_user/vduse_dev.c
>> +++ b/drivers/vdpa/vdpa_user/vduse_dev.c
>> @@ -1512,7 +1512,8 @@ static int vduse_create_dev(struct vduse_dev_config *config,
>>   	dev->config_size = config->config_size;
>>   	dev->vq_align = config->vq_align;
>>   	dev->vq_num = config->vq_num;
>> -	dev->vqs = kcalloc(dev->vq_num, sizeof(*dev->vqs), GFP_KERNEL);
>> +	dev->vqs = kcalloc(dev->vq_num, sizeof(*dev->vqs),
>> +			   GFP_KERNEL | __GFP_NOWARN);
>>   	if (!dev->vqs)
>>   		goto err_vqs;
> 

Thanks for checking the patch.

> This is insufficient - the real source of the problem is that
> vq_num is not validated.
> The thing to do is to validate config and limit vq_num to 0xffff;
> 

1557 static long vduse_ioctl(struct file *file, unsigned int cmd,
1558                         unsigned long arg)
1559 {
1560         int ret;
1561         void __user *argp = (void __user *)arg;
1564         mutex_lock(&vduse_lock);
1565         switch (cmd) {
              ....
1584         case VDUSE_CREATE_DEV: {
1585                 struct vduse_dev_config config;
1587                 void *buf;
1588
1589                 ret = -EFAULT;
1590                 if (copy_from_user(&config, argp, size))
1591                         break;
1592
1593                 ret = -EINVAL;
1594                 if (vduse_validate_config(&config) == false)
1595                         break;
1596
1597                 buf = vmemdup_user(argp + size, config.config_size);
1598                 if (IS_ERR(buf)) {
1599                         ret = PTR_ERR(buf);
1600                         break;
1601                 }
1602                 config.name[VDUSE_NAME_MAX - 1] = '\0';
1603                 ret = vduse_create_dev(&config, buf, 
control->api_version);
1604                 if (ret)
1605                         kvfree(buf);
1606                 break;
1607         }

we have vduse_validate_config() being called in vduse_ioctl() which is 
the caller of vduse_create_dev(), so validate_config() is not necessary 
in vduse_create_dev() ?

Thanks,
Harshit

> 
>> -- 
>> 2.38.1
>