Fix bounds check bug in __register_chrdev_region

The code in __register_chrdev_region checks that if the driver wishing to register has the same major as an existing driver the new minor range is strictly less than the existing minor range. However, it does not also check that the new minor range is strictly greater than the existing minor range. That is, if driver X has registered with major=x and minor=0-3, __register_chrdev_region will allow driver Y to register with major=x and minor=1-4.

I came across this in the context of the Xen virtual console driver, but I imagine it causes a problem for any driver with the same major number but different minor numbers as a driver that has registered ahead of it.

---

 fs/char_dev.c |    7 +++++--
 1 files changed, 5 insertions(+), 2 deletions(-)

5127ecec5817868799c55ac27e8d1651308d1497

index 3483d3c..11c0249 100644
@@ -109,10 +109,13 @@ __register_chrdev_region(unsigned int ma
 
 	for (cp = &chrdevs[i]; *cp; cp = &(*cp)->next)
 		if ((*cp)->major > major ||
-		    ((*cp)->major == major && (*cp)->baseminor >= baseminor))
+		    ((*cp)->major == major &&
+		     (((*cp)->baseminor >= baseminor) ||
+		      ((*cp)->baseminor + (*cp)->minorct > baseminor))))
 			break;
 	if (*cp && (*cp)->major == major &&
-	    (*cp)->baseminor < baseminor + minorct) {
+	    (((*cp)->baseminor < baseminor + minorct) ||
+	     ((*cp)->baseminor + (*cp)->minorct > baseminor))) {
 		ret = -EBUSY;
 		goto out;
 	}

1.0.4