This patch fixes the behaviour of __register_chrdev_region.
Old implemention allowed registering a region which fully contains
an existing one. For example, if we made subseqent calls
__register_chrdev_region(8,5,5,"a")
__register_chrdev_region(8,0,15,"a")
both would have finished successfully, which is not supposed to happen.
---
fs/char_dev.c | 18 ++++++------------
1 file changed, 6 insertions(+), 12 deletions(-)
diff --git a/fs/char_dev.c b/fs/char_dev.c
index 687471d..93a28f2 100644
--- a/fs/char_dev.c
+++ b/fs/char_dev.c
@@ -118,19 +118,13 @@ __register_chrdev_region(unsigned int major, unsigned int baseminor,
/* 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;
+ int intersection_begin = max((*cp)->baseminor, baseminor);
+ int intersection_end = min(
+ (*cp)->baseminor + (*cp)->minorct,
+ baseminor + minorct);
- /* 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) {
+ /* Intersection is nonempty */
+ if (intersection_begin < intersection_end) {
ret = -EBUSY;
goto out;
}
--
2.9.0
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