From: Zijun Hu <zijun.hu@oss.qualcomm.com>
Currently, It is allowed to register miscdevice with minor > 255
which is defined by macro MISC_DYNAMIC_MINOR, and cause:
- Chaos regarding division and management of minor codes.
- Registering failure if the minor was allocated to other dynamic request.
Fortunately, in-kernel users have not had such usage yet.
Fix by refusing to register miscdevice whose minor > 255.
Also bring in a very simple minor code space division and management:
< 255 : Fixed minor code
== 255 : Indicator to request dynamic minor code
> 255 : Dynamic minor code requested, 1048320 minor codes totally
And all fixed minors allocated should be registered in 'linux/miscdevice.h'
Signed-off-by: Zijun Hu <zijun.hu@oss.qualcomm.com>
---
drivers/char/misc.c | 6 ++++++
include/linux/miscdevice.h | 8 ++++++++
2 files changed, 14 insertions(+)
diff --git a/drivers/char/misc.c b/drivers/char/misc.c
index 558302a64dd908aee30341547a5413df1af71459..b8e66466184fa21fb66d968db7950e0b5669ac43 100644
--- a/drivers/char/misc.c
+++ b/drivers/char/misc.c
@@ -210,6 +210,12 @@ int misc_register(struct miscdevice *misc)
int err = 0;
bool is_dynamic = (misc->minor == MISC_DYNAMIC_MINOR);
+ if (misc->minor > MISC_DYNAMIC_MINOR) {
+ pr_err("Invalid fixed minor %d for miscdevice '%s'\n",
+ misc->minor, misc->name);
+ return -EINVAL;
+ }
+
INIT_LIST_HEAD(&misc->list);
mutex_lock(&misc_mtx);
diff --git a/include/linux/miscdevice.h b/include/linux/miscdevice.h
index 3e6deb00fc8535a7571f85489c74979e18385bad..565b88efeb23d02b7d91df1cd7df4bdcf2898224 100644
--- a/include/linux/miscdevice.h
+++ b/include/linux/miscdevice.h
@@ -71,6 +71,14 @@
#define USERIO_MINOR 240
#define VHOST_VSOCK_MINOR 241
#define RFKILL_MINOR 242
+
+/*
+ * Misc char device minor code space division related to below macro:
+ *
+ * < 255 : Fixed minor code
+ * == 255 : Indicator to request dynamic minor code
+ * > 255 : Dynamic minor code requested, 1048320 minor codes totally.
+ */
#define MISC_DYNAMIC_MINOR 255
struct miscdevice {
--
2.34.1