Hi Dan,
On Sat, Nov 26, 2016 at 12:57:17PM +0300, Dan Carpenter wrote:
> Hello Sean Young,
>
> The patch afbb110172b9: "[media] lirc: prevent use-after free" from
> Oct 31, 2016, leads to the following static checker warning:
>
> drivers/media/rc/lirc_dev.c:190 lirc_cdev_add()
> error: potential null dereference 'cdev'. (cdev_alloc returns null)
>
> drivers/media/rc/lirc_dev.c
> 158 static int lirc_cdev_add(struct irctl *ir)
> 159 {
> 160 int retval = -ENOMEM;
> 161 struct lirc_driver *d = &ir->d;
> 162 struct cdev *cdev;
> 163
> 164 cdev = cdev_alloc();
> 165 if (!cdev)
> 166 goto err_out;
>
> Classic one err bug. Just return directly here. return -ENOMEM is 100%
> readable but goto err_out is opaque because you first have to scroll
> down to see what err_out does then you have to scroll to the start of
> the function to verify that retval is set.
>
> 167
> 168 if (d->fops) {
> 169 cdev->ops = d->fops;
> 170 cdev->owner = d->owner;
> 171 } else {
> 172 cdev->ops = &lirc_dev_fops;
> 173 cdev->owner = THIS_MODULE;
> 174 }
> 175 retval = kobject_set_name(&cdev->kobj, "lirc%d", d->minor);
> 176 if (retval)
> 177 goto err_out;
> 178
> 179 retval = cdev_add(cdev, MKDEV(MAJOR(lirc_base_dev),
> d->minor), 1);
> 180 if (retval) {
> 181 kobject_put(&cdev->kobj);
>
> This is a double free, isn't it? It should just be goto del_cdev;
>
> 182 goto err_out;
> 183 }
> 184
> 185 ir->cdev = cdev;
> 186
> 187 return 0;
> 188
> 189 err_out:
> 190 cdev_del(cdev);
>
> Can't pass NULLs to this function.
>
> 191 return retval;
> 192 }
Oh dear! Thanks for reporting this, you're absolutely right. I'll send
out a patch shortly.
Thanks
Sean
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