Re: [PATCH] vduse: Fix a possible warning in vduse_create_dev()

[Michael S. Tsirkin]

On Sun, Nov 27, 2022 at 08:16:24AM +0530, Harshit Mogalapalli wrote:
> 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@xxxxxxxxxx>
> > > ---
> > >   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

OK but I don't see vduse_validate_config checking vq_num.

> > 
> > > -- 
> > > 2.38.1
> >