• Kees Cook's avatar
    param: do not set store func without write perm · b0a65b0c
    Kees Cook authored
    When a module_param is defined without DAC write permissions, it can
    still be changed at runtime and updated. Drivers using a 0444 permission
    may be surprised that these values can still be changed.
    
    For drivers that want to allow updates, any S_IW* flag will set the
    "store" function as before. Drivers without S_IW* flags will have the
    "store" function unset, unforcing a read-only value. Drivers that wish
    neither "store" nor "get" can continue to use "0" for perms to stay out
    of sysfs entirely.
    
    Old behavior:
      # cd /sys/module/snd/parameters
      # ls -l
      total 0
      -r--r--r-- 1 root root 4096 Dec 11 13:55 cards_limit
      -r--r--r-- 1 root root 4096 Dec 11 13:55 major
      -r--r--r-- 1 root root 4096 Dec 11 13:55 slots
      # cat major
      116
      # echo -1 > major
      -bash: major: Permission denied
      # chmod u+w major
      # echo -1 > major
      # cat major
      -1
    
    New behavior:
      ...
      # chmod u+w major
      # echo -1 > major
      -bash: echo: write error: Input/output error
    Signed-off-by: default avatarKees Cook <keescook@chromium.org>
    Signed-off-by: default avatarRusty Russell <rusty@rustcorp.com.au>
    b0a65b0c
params.c 22.4 KB