* [PATCH] char: misc: restore MISC_DYNAMIC_MINOR on device_create() failure
@ 2015-05-18 17:11 Vladimir Zapolskiy
0 siblings, 0 replies; only message in thread
From: Vladimir Zapolskiy @ 2015-05-18 17:11 UTC (permalink / raw
To: Arnd Bergmann, Greg Kroah-Hartman; +Cc: linux-kernel
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>
---
drivers/char/misc.c | 13 +++++++++----
1 file changed, 9 insertions(+), 4 deletions(-)
diff --git a/drivers/char/misc.c b/drivers/char/misc.c
index 9fd5a91..5113409 100644
--- a/drivers/char/misc.c
+++ b/drivers/char/misc.c
@@ -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)) {
- int i = DYNAMIC_MINORS - misc->minor - 1;
- if (i < DYNAMIC_MINORS && i >= 0)
- clear_bit(i, misc_minors);
+ 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;
}
--
2.1.4
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2015-05-18 17:11 [PATCH] char: misc: restore MISC_DYNAMIC_MINOR on device_create() failure Vladimir Zapolskiy
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