6.6-stable review patch. If anyone has any objections, please let me know.
------------------
From: Thadeu Lima de Souza Cascardo cascardo@igalia.com
commit c876be906ce7e518d9ef9926478669c151999e69 upstream.
register_chrdev will only register the first 256 minors of a major chrdev. That means that dynamically allocated misc devices with minor above 255 will fail to open with -ENXIO.
This was found by kernel test robot when testing a different change that makes all dynamically allocated minors be above 255. This has, however, been separately tested by creating 256 serio_raw devices with the help of userio driver.
Ever since allowing misc devices with minors above 128, this has been possible.
Fix it by registering all minor numbers from 0 to MINORMASK + 1 for MISC_MAJOR.
Reported-by: kernel test robot oliver.sang@intel.com Cc: stable stable@kernel.org Closes: https://lore.kernel.org/oe-lkp/202503171507.6c8093d0-lkp@intel.com Fixes: ab760791c0cf ("char: misc: Increase the maximum number of dynamic misc devices to 1048448") Signed-off-by: Thadeu Lima de Souza Cascardo cascardo@igalia.com Tested-by: Hou Wenlong houwenlong.hwl@antgroup.com Link: https://lore.kernel.org/r/20250317-misc-chrdev-v1-1-6cd05da11aef@igalia.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/char/misc.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/drivers/char/misc.c +++ b/drivers/char/misc.c @@ -315,7 +315,7 @@ static int __init misc_init(void) goto fail_remove;
err = -EIO; - if (register_chrdev(MISC_MAJOR, "misc", &misc_fops)) + if (__register_chrdev(MISC_MAJOR, 0, MINORMASK + 1, "misc", &misc_fops)) goto fail_printk; return 0;