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

[Colin King (gmail)]

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