Re: [PATCH 03/23] lib: uaccess: provide getline_from_user()

[Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>]

On Fri, Sep 04, 2020 at 05:45:27PM +0200, Bartosz Golaszewski wrote:
> From: Bartosz Golaszewski <bgolaszewski@xxxxxxxxxxxx>
> 
> Provide a uaccess helper that allows callers to copy a single line from
> user memory. This is useful for debugfs write callbacks.

Doesn't mm/util.c provides us something like this?
strndup_user()?

> 
> Signed-off-by: Bartosz Golaszewski <bgolaszewski@xxxxxxxxxxxx>
> ---
>  include/linux/uaccess.h |  3 +++
>  lib/usercopy.c          | 37 +++++++++++++++++++++++++++++++++++++
>  2 files changed, 40 insertions(+)
> 
> diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
> index 94b285411659..5aedd8ac5c31 100644
> --- a/include/linux/uaccess.h
> +++ b/include/linux/uaccess.h
> @@ -333,6 +333,9 @@ long strncpy_from_user_nofault(char *dst, const void __user *unsafe_addr,
>  		long count);
>  long strnlen_user_nofault(const void __user *unsafe_addr, long count);
>  
> +ssize_t getline_from_user(char *dst, size_t dst_size,
> +			  const char __user *src, size_t src_size);
> +
>  /**
>   * get_kernel_nofault(): safely attempt to read from a location
>   * @val: read into this variable
> diff --git a/lib/usercopy.c b/lib/usercopy.c
> index b26509f112f9..55aaaf93d847 100644
> --- a/lib/usercopy.c
> +++ b/lib/usercopy.c
> @@ -87,3 +87,40 @@ int check_zeroed_user(const void __user *from, size_t size)
>  	return -EFAULT;
>  }
>  EXPORT_SYMBOL(check_zeroed_user);
> +
> +/**
> + * getline_from_user - Copy a single line from user
> + * @dst: Where to copy the line to
> + * @dst_size: Size of the destination buffer
> + * @src: Where to copy the line from
> + * @src_size: Size of the source user buffer
> + *
> + * Copies a number of characters from given user buffer into the dst buffer.
> + * The number of bytes is limited to the lesser of the sizes of both buffers.
> + * If the copied string contains a newline, its first occurrence is replaced
> + * by a NULL byte in the destination buffer. Otherwise the function ensures
> + * the copied string is NULL-terminated.
> + *
> + * Returns the number of copied bytes or a negative error number on failure.
> + */
> +
> +ssize_t getline_from_user(char *dst, size_t dst_size,
> +			  const char __user *src, size_t src_size)
> +{
> +	size_t size = min_t(size_t, dst_size, src_size);
> +	char *c;
> +	int ret;
> +
> +	ret = copy_from_user(dst, src, size);
> +	if (ret)
> +		return -EFAULT;
> +
> +	dst[size - 1] = '\0';
> +
> +	c = strchrnul(dst, '\n');
> +	if (*c)
> +		*c = '\0';
> +
> +	return c - dst;
> +}
> +EXPORT_SYMBOL(getline_from_user);
> -- 
> 2.26.1
> 

-- 
With Best Regards,
Andy Shevchenko