Commit b575f712 authored May 18, 2015 by Vladimir Zapolskiy Committed by Greg Kroah-Hartman Jun 01, 2015

char: misc: restore MISC_DYNAMIC_MINOR on device_create() failure

On attempt to register a dynamic minor misc device its minor number is
updated to a virtual minor number prior to device_create() call,
however on error path misc->minor == MISC_DYNAMIC_MINOR is not
restored.

Following the rule of thumb that a function returning an error must
not change the state of the caller, assign MISC_DYNAMIC_MINOR back.

The problem is met in a sutuation, when subsys_initcall(misc_init) is
not yet called and misc_class is not created, but misc_register()
modifies statically defined ".minor = MISC_DYNAMIC_MINOR", therefore
implicitly changing the client's logic on next attempt (e.g. retrying
from deferred list) to register a misc device, whose minor number is
converted from dynamic to some unknown static one.

Signed-off-by: Vladimir Zapolskiy <vladimir_zapolskiy@mentor.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent b144ce2d

drivers/char/misc.c

+9 −4

Original line number	Diff line number	Diff line
		@@ -186,12 +186,13 @@ int misc_register(struct miscdevice * misc)
		{
		dev_t dev;
		int err = 0;
		bool is_dynamic = (misc->minor == MISC_DYNAMIC_MINOR);

		INIT_LIST_HEAD(&misc->list);

		mutex_lock(&misc_mtx);

		if (misc->minor == MISC_DYNAMIC_MINOR) {
		if (is_dynamic) {
		int i = find_first_zero_bit(misc_minors, DYNAMIC_MINORS);
		if (i >= DYNAMIC_MINORS) {
		err = -EBUSY;
		@@ -216,9 +217,13 @@ int misc_register(struct miscdevice * misc)
		device_create_with_groups(misc_class, misc->parent, dev,
		misc, misc->groups, "%s", misc->name);
		if (IS_ERR(misc->this_device)) {
		if (is_dynamic) {
		int i = DYNAMIC_MINORS - misc->minor - 1;

		if (i < DYNAMIC_MINORS && i >= 0)
		clear_bit(i, misc_minors);
		misc->minor = MISC_DYNAMIC_MINOR;
		}
		err = PTR_ERR(misc->this_device);
		goto out;
		}