Re: [PATCH] tty: vt: add a bounds checking in vt_do_kdgkb_ioctl()

[kernel test robot]

Hi Hangyu,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on tty/tty-testing]
[also build test WARNING on linus/master v6.0-rc4 next-20220908]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Hangyu-Hua/tty-vt-add-a-bounds-checking-in-vt_do_kdgkb_ioctl/20220908-155511
base:   https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty.git tty-testing
config: x86_64-randconfig-a005 (https://download.01.org/0day-ci/archive/20220908/202209082101.rCth0nPs-lkp@xxxxxxxxx/config)
compiler: clang version 14.0.6 (https://github.com/llvm/llvm-project f28c006a5895fc0e329fe15fead81e37457cb1d1)
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # https://github.com/intel-lab-lkp/linux/commit/9878c90ddacf7a81079f77b10502496c4d6cd0cb
        git remote add linux-review https://github.com/intel-lab-lkp/linux
        git fetch --no-tags linux-review Hangyu-Hua/tty-vt-add-a-bounds-checking-in-vt_do_kdgkb_ioctl/20220908-155511
        git checkout 9878c90ddacf7a81079f77b10502496c4d6cd0cb
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=x86_64 SHELL=/bin/bash drivers/tty/vt/ fs/ext4/

If you fix the issue, kindly add following tag where applicable
Reported-by: kernel test robot <lkp@xxxxxxxxx>

All warnings (new ones prefixed by >>):

>> drivers/tty/vt/keyboard.c:2070:14: warning: result of comparison of constant 256 with expression of type 'unsigned char' is always false [-Wtautological-constant-out-of-range-compare]
           if (kb_func >= MAX_NR_FUNC)
               ~~~~~~~ ^  ~~~~~~~~~~~
   1 warning generated.


vim +2070 drivers/tty/vt/keyboard.c

  2059	
  2060	int vt_do_kdgkb_ioctl(int cmd, struct kbsentry __user *user_kdgkb, int perm)
  2061	{
  2062		unsigned char kb_func;
  2063		unsigned long flags;
  2064		char *kbs;
  2065		int ret;
  2066	
  2067		if (get_user(kb_func, &user_kdgkb->kb_func))
  2068			return -EFAULT;
  2069	
> 2070		if (kb_func >= MAX_NR_FUNC)
  2071			return -EFAULT;
  2072	
  2073		kb_func = array_index_nospec(kb_func, MAX_NR_FUNC);
  2074	
  2075		switch (cmd) {
  2076		case KDGKBSENT: {
  2077			/* size should have been a struct member */
  2078			ssize_t len = sizeof(user_kdgkb->kb_string);
  2079	
  2080			kbs = kmalloc(len, GFP_KERNEL);
  2081			if (!kbs)
  2082				return -ENOMEM;
  2083	
  2084			spin_lock_irqsave(&func_buf_lock, flags);
  2085			len = strlcpy(kbs, func_table[kb_func] ? : "", len);
  2086			spin_unlock_irqrestore(&func_buf_lock, flags);
  2087	
  2088			ret = copy_to_user(user_kdgkb->kb_string, kbs, len + 1) ?
  2089				-EFAULT : 0;
  2090	
  2091			break;
  2092		}
  2093		case KDSKBSENT:
  2094			if (!perm || !capable(CAP_SYS_TTY_CONFIG))
  2095				return -EPERM;
  2096	
  2097			kbs = strndup_user(user_kdgkb->kb_string,
  2098					sizeof(user_kdgkb->kb_string));
  2099			if (IS_ERR(kbs))
  2100				return PTR_ERR(kbs);
  2101	
  2102			spin_lock_irqsave(&func_buf_lock, flags);
  2103			kbs = vt_kdskbsent(kbs, kb_func);
  2104			spin_unlock_irqrestore(&func_buf_lock, flags);
  2105	
  2106			ret = 0;
  2107			break;
  2108		}
  2109	
  2110		kfree(kbs);
  2111	
  2112		return ret;
  2113	}
  2114	

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