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Subject[PATCH 1/2] chardev: fix an overlap misjudgement case in __register_chrdev_region()
Date
Current overlap check of minor range cannot correctly
handle a case which is baseminor < existing baseminor &&
baseminor + minorct > existing baseminor + minorct.
Fix it and meanwhile do some code cleanups.

Fixes: 01d553d0fe9f90 ("Chardev checking of overlapping ranges")
Signed-off-by: Chengguang Xu <cgxu519@gmx.com>
Cc: stable@vger.kernel.org
---
fs/char_dev.c | 94 ++++++++++++++++++++++++---------------------------
1 file changed, 44 insertions(+), 50 deletions(-)

diff --git a/fs/char_dev.c b/fs/char_dev.c
index a279c58fe360..b25b1da097d5 100644
--- a/fs/char_dev.c
+++ b/fs/char_dev.c
@@ -88,86 +88,80 @@ static int find_dynamic_major(void)
/*
* Register a single major with a specified minor range.
*
- * If major == 0 this functions will dynamically allocate a major and return
- * its number.
- *
- * If major > 0 this function will attempt to reserve the passed range of
- * minors and will return zero on success.
+ * If major == 0 this function will dynamically allocate an unused major,
+ * otherwise attempt to reserve the range of minors with given major.
*
- * Returns a -ve errno on failure.
*/
static struct char_device_struct *
__register_chrdev_region(unsigned int major, unsigned int baseminor,
int minorct, const char *name)
{
- struct char_device_struct *cd, **cp;
- int ret = 0;
+ struct char_device_struct *new, *curr, *prev = NULL;
+ int ret = -EBUSY;
int i;

- cd = kzalloc(sizeof(struct char_device_struct), GFP_KERNEL);
- if (cd == NULL)
+ if (major >= CHRDEV_MAJOR_MAX) {
+ pr_err("CHRDEV \"%s\" major requested (%u) is greater than the maximum (%u)\n",
+ name, major, CHRDEV_MAJOR_MAX-1);
+ return ERR_PTR(-EINVAL);
+ }
+
+ if (minorct > MINORMASK + 1 - baseminor) {
+ pr_err("CHRDEV \"%s\" minor range requested (%u-%u) is out of range of maximum range (%u-%u) for a single major\n",
+ name, baseminor, baseminor + minorct - 1, 0, MINORMASK);
+ return ERR_PTR(-EINVAL);
+ }
+
+ new = kzalloc(sizeof(struct char_device_struct), GFP_KERNEL);
+ if (new == NULL)
return ERR_PTR(-ENOMEM);

mutex_lock(&chrdevs_lock);

if (major == 0) {
- ret = find_dynamic_major();
- if (ret < 0) {
+ major = find_dynamic_major();
+ if (major < 0) {
pr_err("CHRDEV \"%s\" dynamic allocation region is full\n",
name);
goto out;
}
- major = ret;
}

- if (major >= CHRDEV_MAJOR_MAX) {
- pr_err("CHRDEV \"%s\" major requested (%u) is greater than the maximum (%u)\n",
- name, major, CHRDEV_MAJOR_MAX-1);
- ret = -EINVAL;
- goto out;
- }
-
- cd->major = major;
- cd->baseminor = baseminor;
- cd->minorct = minorct;
- strlcpy(cd->name, name, sizeof(cd->name));
-
i = major_to_index(major);
+ for (curr = chrdevs[i]; curr; prev = curr, curr = curr->next) {
+ if (curr->major < major)
+ continue;

- for (cp = &chrdevs[i]; *cp; cp = &(*cp)->next)
- if ((*cp)->major > major ||
- ((*cp)->major == major &&
- (((*cp)->baseminor >= baseminor) ||
- ((*cp)->baseminor + (*cp)->minorct > baseminor))))
+ if (curr->major > major)
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;
+ if (curr->baseminor + curr->minorct <= baseminor)
+ continue;

- /* New driver overlaps from the left. */
- if (new_max >= old_min && new_max <= old_max) {
- ret = -EBUSY;
- goto out;
- }
+ if (curr->baseminor >= baseminor + minorct)
+ break;

- /* New driver overlaps from the right. */
- if (new_min <= old_max && new_min >= old_min) {
- ret = -EBUSY;
- goto out;
- }
+ goto out;
+ }
+
+ new->major = major;
+ new->baseminor = baseminor;
+ new->minorct = minorct;
+ strlcpy(new->name, name, sizeof(new->name));
+
+ if (!prev) {
+ new->next = curr;
+ chrdevs[i] = new;
+ } else {
+ new->next = prev->next;
+ prev->next = new;
}

- cd->next = *cp;
- *cp = cd;
mutex_unlock(&chrdevs_lock);
- return cd;
+ return new;
out:
mutex_unlock(&chrdevs_lock);
- kfree(cd);
+ kfree(new);
return ERR_PTR(ret);
}

--
2.20.1
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