[PATCH] cdev: cdev_put oops

While fixing an oops in the st driver in a dirty release path, I
encountered an oops in cdev_put for cdevs allocated using cdev_alloc.  If
cdev_del is called when the cdev kobject still has an open user, when the
last cdev_put is called, the cdev_put will call kobject_put, which will end
up ultimately releasing the cdev in cdev_dynamic_release.  Patch fixes the
oops by preventing cdev_put from accessing freed memory.

Signed-off-by: Brian King <brking@us.ibm.com>
Cc: <viro@parcelfarce.linux.theplanet.co.uk>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/fs/char_dev.c b/fs/char_dev.c
index a69a5d8a406f982be7eb6cb1fc9c4ff59a858ffa..3b1b1eefdbb01686f127df582143f922bf87c193 100644 (file)
--- a/fs/char_dev.c
+++ b/fs/char_dev.c
@@ -277,8 +277,9 @@ static struct kobject *cdev_get(struct cdev *p)
 void cdev_put(struct cdev *p)
 {
        if (p) {
+               struct module *owner = p->owner;
                kobject_put(&p->kobj);
-               module_put(p->owner);
+               module_put(owner);
        }
 }