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[PATCH] Chardev checking of overlapping ranges
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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.

Signed-off-by: Amos Waterland <[email protected]>
Cc: Linas Vepstas <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
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Amos Waterland authored and Linus Torvalds committed Sep 29, 2006
1 parent f400e19 commit 01d553d
Showing 1 changed file with 23 additions and 5 deletions.
28 changes: 23 additions & 5 deletions fs/char_dev.c
Original file line number Diff line number Diff line change
Expand Up @@ -128,13 +128,31 @@ __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)->major == major &&
(((*cp)->baseminor >= baseminor) ||
((*cp)->baseminor + (*cp)->minorct > baseminor))))
break;
if (*cp && (*cp)->major == major &&
(*cp)->baseminor < baseminor + minorct) {
ret = -EBUSY;
goto out;

/* 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;
}
}

cd->next = *cp;
*cp = cd;
mutex_unlock(&chrdevs_lock);
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