From f5597840ac907858ad2a462b00e4a68fd199121e Mon Sep 17 00:00:00 2001 From: Zijun Hu Date: Mon, 14 Jul 2025 23:34:14 +0800 Subject: [PATCH] char: misc: Disallow registering miscdevice whose minor > MISC_DYNAMIC_MINOR 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 Link: https://lore.kernel.org/r/20250714-rfc_miscdev-v6-3-2ed949665bde@oss.qualcomm.com Signed-off-by: Greg Kroah-Hartman --- 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 558302a64dd90..b8e66466184fa 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 3e6deb00fc853..565b88efeb23d 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 { -- 2.47.3