Re: [PATCH v2] smackfs: restrict bytes count in smackfs write functions

[Tetsuo Handa]

On 2021/01/28 20:58, Sabyrzhan Tasbolatov wrote:
> @@ -2005,6 +2009,9 @@ static ssize_t smk_write_onlycap(struct file *file, 
> const char __user *buf,
>       if (!smack_privileged(CAP_MAC_ADMIN))
>               return -EPERM;
>  
> +     if (count > PAGE_SIZE)
> +             return -EINVAL;
> +
>       data = memdup_user_nul(buf, count);
>       if (IS_ERR(data))
>               return PTR_ERR(data);
> @@ -2740,10 +2754,13 @@ static ssize_t smk_write_relabel_self(struct file 
> *file, const char __user *buf,
>               return -EPERM;
>  
>       /*
> +      * No partial write.
>        * Enough data must be present.
>        */
>       if (*ppos != 0)
>               return -EINVAL;
> +     if (count == 0 || count > PAGE_SIZE)
> +             return -EINVAL;
>  
>       data = memdup_user_nul(buf, count);
>       if (IS_ERR(data))
> 

Doesn't this change break legitimate requests like

  char buffer[20000];

  memset(buffer, ' ', sizeof(buffer));
  memcpy(buffer + sizeof(buffer) - 10, "foo", 3);
  write(fd, buffer, sizeof(buffer));

?