On Wed, May 25, 2016 at 10:53:36PM +0800, Gavin Chang wrote:
> Hi,
>
> I'm a new person to learn Linux kernel.
>
> In fs/char_dev.c function __register_chrdev_region(), there is the
> following code:
>
> for (cp = &chrdevs[i]; *cp; cp = &(*cp)->next)
> if ((*cp)->major > major ||
> ((*cp)->major == major &&
> (((*cp)->baseminor >= baseminor) ||
> ((*cp)->baseminor + (*cp)->minorct > baseminor))))
> break;
>
> /* Check for overlapping minor ranges. */
> if (*cp && (*cp)->major == major) {
> int old_min = (*cp)->baseminor;
> int old_max = (*cp)->baseminor + (*cp)->minorct - 1;
> int new_min = baseminor;
> int new_max = baseminor + minorct - 1;
>
> /* New driver overlaps from the left. */
> if (new_max >= old_min && new_max <= old_max) {
> ret = -EBUSY;
> goto out;
> }
>
> /* New driver overlaps from the right. */
> if (new_min <= old_max && new_min >= old_min) {
> ret = -EBUSY;
> goto out;
> }
> }
>
> I think there is a bug in checking of overlapping ranges.
> For example, driver X has registered with major=x and minor=1-3, and
> __register_chrdev_region() will allow driver Y to register with
> major=x and minor=0-4.
> The minor of driver Y will not meet the two if statements:
> if (new_max >= old_min && new_max <= old_max) and if (new_min <=
> old_max && new_min >= old_min)
>
> The attached is my patch to repair this problem.
> And there is a related commit 01d553d0fe9f90a132c5ff494872be8d4126be1e
> for reference.
> diff --git a/fs/char_dev.c b/fs/char_dev.c
> index 24b1425..d65765e 100644
> --- a/fs/char_dev.c
> +++ b/fs/char_dev.c
> @@ -107,29 +107,14 @@ __register_chrdev_region(unsigned int major, unsigned int baseminor,
>
> for (cp = &chrdevs[i]; *cp; cp = &(*cp)->next)
> if ((*cp)->major > major ||
> - ((*cp)->major == major &&
> - (((*cp)->baseminor >= baseminor) ||
> - ((*cp)->baseminor + (*cp)->minorct > baseminor))))
> + ((*cp)->major == major && ((*cp)->baseminor + (*cp)->minorct > baseminor)))
> break;
>
> /* Check for overlapping minor ranges. */
> - if (*cp && (*cp)->major == major) {
> - int old_min = (*cp)->baseminor;
> - int old_max = (*cp)->baseminor + (*cp)->minorct - 1;
> - int new_min = baseminor;
> - int new_max = baseminor + minorct - 1;
> -
> - /* New driver overlaps from the left. */
> - if (new_max >= old_min && new_max <= old_max) {
> - ret = -EBUSY;
> - goto out;
> - }
> -
> - /* New driver overlaps from the right. */
> - if (new_min <= old_max && new_min >= old_min) {
> - ret = -EBUSY;
> - goto out;
> - }
> + if (*cp && (*cp)->major == major &&
> + (*cp)->baseminor < baseminor + minorct) {
> + ret = -EBUSY;
> + goto out;
> }
>
> cd->next = *cp;
Gavin,
You're going to want to read Documentation/SubmittingPatches. Basically,
you want to use git commit -s, git format-patch, and git send-email
rather than attachments.
Thanks,
--
Omar
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