[RFC PATCH v2 02/11] vfs: define a generic function to read a file from the kernel

[Luis R. Rodriguez]

On Mon, Jan 18, 2016 at 10:11:17AM -0500, Mimi Zohar wrote:
> diff --git a/fs/exec.c b/fs/exec.c
> index b06623a..6d623c2 100644
> --- a/fs/exec.c
> +++ b/fs/exec.c
> @@ -831,6 +832,58 @@ int kernel_read(struct file *file, loff_t offset,
>  
>  EXPORT_SYMBOL(kernel_read);
>  
> +int kernel_read_file(struct file *file, void **buf, loff_t *size,
> +		     loff_t max_size)
> +{
> +	loff_t i_size, pos;
> +	ssize_t bytes = 0;
> +	int ret;
> +
> +	if (!S_ISREG(file_inode(file)->i_mode))
> +		return -EINVAL;
> +
> +	i_size = i_size_read(file_inode(file));
> +	if (max_size > 0 && i_size > max_size)
> +		return -EFBIG;

loff_t is a __kernel_loff_t, which in turn is a long long, and that's
signed. We don't catch a negative value here, for max_size, we could
return -EINVAL if its < 0.

> +	if (i_size == 0)
> +		return -EINVAL;

Likewise for i_size. The setter of the size will depend on how the
code calling this routine setup the struct file passed.

So how about adding a i_size <= 0 check here as well here?
At least fw_read_file_contents() has historically done this,
so if this generic read is going to skip that I'd like to
see why. We're unifying so I rather be more pedantic.

Provided this is addressed feel free to peg:

Reviewed-by: Luis R. Rodriguez <mcgrof at suse.com>

  Luis