re: btrfs: add btrfs_read_policy_to_enum helper and refactor read, policy store

["Colin King (gmail)" <colin.i.king@gmail.com>]

Hi,

Static analysis on linux-next today has found a potential buffer 
overflow in fs/btrfs/sysfs.c in function btrfs_read_policy_to_enum()

The strcpy to string param has no length checks on str and hence if str 
is longer than param a buffer overflow on the stack occurs. This can 
potentially occur when a user writes a long string to the btrfs sysfs 
file read_policy via btrfs_read_policy_store()

int btrfs_read_policy_to_enum(const char *str, s64 *value)
{
         char param[32] = {'\0'};
         char *__maybe_unused value_str;
         int index;
         bool found = false;

         if (!str || strlen(str) == 0)
                 return 0;

         strcpy(param, str);   /* issue here */

	....
}

Colin