Re: [PATCH v2 1/2] fs/kernel_read_file: Allow to read files up-to ssize_t

[Baoquan He]

On 05/27/22 at 02:55am, Pasha Tatashin wrote:
> Currently, the maximum file size that is supported is 2G. This may be
> too small in some cases. For example, kexec_file_load() system call
> loads initramfs. In some netboot cases initramfs can be rather large.
> 
> Allow to use up-to ssize_t bytes. The callers still can limit the
> maximum file size via buf_size.

If we really met initramfs bigger than 2G, it's reasonable to increase
the limit. While wondering why we should take sszie_t, but not size_t.

> 
> Signed-off-by: Pasha Tatashin <pasha.tatashin@xxxxxxxxxx>
> ---
>  fs/kernel_read_file.c            | 38 ++++++++++++++++----------------
>  include/linux/kernel_read_file.h | 32 +++++++++++++--------------
>  include/linux/limits.h           |  1 +
>  3 files changed, 36 insertions(+), 35 deletions(-)
> 
> diff --git a/fs/kernel_read_file.c b/fs/kernel_read_file.c
> index 1b07550485b9..5d826274570c 100644
> --- a/fs/kernel_read_file.c
> +++ b/fs/kernel_read_file.c
> @@ -29,15 +29,15 @@
>   * change between calls to kernel_read_file().
>   *
>   * Returns number of bytes read (no single read will be bigger
> - * than INT_MAX), or negative on error.
> + * than SSIZE_MAX), or negative on error.
>   *
>   */
> -int kernel_read_file(struct file *file, loff_t offset, void **buf,
> -		     size_t buf_size, size_t *file_size,
> -		     enum kernel_read_file_id id)
> +ssize_t kernel_read_file(struct file *file, loff_t offset, void **buf,
> +			 size_t buf_size, size_t *file_size,
> +			 enum kernel_read_file_id id)
>  {
>  	loff_t i_size, pos;
> -	size_t copied;
> +	ssize_t copied;
>  	void *allocated = NULL;
>  	bool whole_file;
>  	int ret;
> @@ -58,7 +58,7 @@ int kernel_read_file(struct file *file, loff_t offset, void **buf,
>  		goto out;
>  	}
>  	/* The file is too big for sane activities. */
> -	if (i_size > INT_MAX) {
> +	if (i_size > SSIZE_MAX) {
>  		ret = -EFBIG;
>  		goto out;
>  	}
> @@ -124,12 +124,12 @@ int kernel_read_file(struct file *file, loff_t offset, void **buf,
>  }
>  EXPORT_SYMBOL_GPL(kernel_read_file);
>  
> -int kernel_read_file_from_path(const char *path, loff_t offset, void **buf,
> -			       size_t buf_size, size_t *file_size,
> -			       enum kernel_read_file_id id)
> +ssize_t kernel_read_file_from_path(const char *path, loff_t offset, void **buf,
> +				   size_t buf_size, size_t *file_size,
> +				   enum kernel_read_file_id id)
>  {
>  	struct file *file;
> -	int ret;
> +	ssize_t ret;
>  
>  	if (!path || !*path)
>  		return -EINVAL;
> @@ -144,14 +144,14 @@ int kernel_read_file_from_path(const char *path, loff_t offset, void **buf,
>  }
>  EXPORT_SYMBOL_GPL(kernel_read_file_from_path);
>  
> -int kernel_read_file_from_path_initns(const char *path, loff_t offset,
> -				      void **buf, size_t buf_size,
> -				      size_t *file_size,
> -				      enum kernel_read_file_id id)
> +ssize_t kernel_read_file_from_path_initns(const char *path, loff_t offset,
> +					  void **buf, size_t buf_size,
> +					  size_t *file_size,
> +					  enum kernel_read_file_id id)
>  {
>  	struct file *file;
>  	struct path root;
> -	int ret;
> +	ssize_t ret;
>  
>  	if (!path || !*path)
>  		return -EINVAL;
> @@ -171,12 +171,12 @@ int kernel_read_file_from_path_initns(const char *path, loff_t offset,
>  }
>  EXPORT_SYMBOL_GPL(kernel_read_file_from_path_initns);
>  
> -int kernel_read_file_from_fd(int fd, loff_t offset, void **buf,
> -			     size_t buf_size, size_t *file_size,
> -			     enum kernel_read_file_id id)
> +ssize_t kernel_read_file_from_fd(int fd, loff_t offset, void **buf,
> +				 size_t buf_size, size_t *file_size,
> +				 enum kernel_read_file_id id)
>  {
>  	struct fd f = fdget(fd);
> -	int ret = -EBADF;
> +	ssize_t ret = -EBADF;
>  
>  	if (!f.file || !(f.file->f_mode & FMODE_READ))
>  		goto out;
> diff --git a/include/linux/kernel_read_file.h b/include/linux/kernel_read_file.h
> index 575ffa1031d3..90451e2e12bd 100644
> --- a/include/linux/kernel_read_file.h
> +++ b/include/linux/kernel_read_file.h
> @@ -35,21 +35,21 @@ static inline const char *kernel_read_file_id_str(enum kernel_read_file_id id)
>  	return kernel_read_file_str[id];
>  }
>  
> -int kernel_read_file(struct file *file, loff_t offset,
> -		     void **buf, size_t buf_size,
> -		     size_t *file_size,
> -		     enum kernel_read_file_id id);
> -int kernel_read_file_from_path(const char *path, loff_t offset,
> -			       void **buf, size_t buf_size,
> -			       size_t *file_size,
> -			       enum kernel_read_file_id id);
> -int kernel_read_file_from_path_initns(const char *path, loff_t offset,
> -				      void **buf, size_t buf_size,
> -				      size_t *file_size,
> -				      enum kernel_read_file_id id);
> -int kernel_read_file_from_fd(int fd, loff_t offset,
> -			     void **buf, size_t buf_size,
> -			     size_t *file_size,
> -			     enum kernel_read_file_id id);
> +ssize_t kernel_read_file(struct file *file, loff_t offset,
> +			 void **buf, size_t buf_size,
> +			 size_t *file_size,
> +			 enum kernel_read_file_id id);
> +ssize_t kernel_read_file_from_path(const char *path, loff_t offset,
> +				   void **buf, size_t buf_size,
> +				   size_t *file_size,
> +				   enum kernel_read_file_id id);
> +ssize_t kernel_read_file_from_path_initns(const char *path, loff_t offset,
> +					  void **buf, size_t buf_size,
> +					  size_t *file_size,
> +					  enum kernel_read_file_id id);
> +ssize_t kernel_read_file_from_fd(int fd, loff_t offset,
> +				 void **buf, size_t buf_size,
> +				 size_t *file_size,
> +				 enum kernel_read_file_id id);
>  
>  #endif /* _LINUX_KERNEL_READ_FILE_H */
> diff --git a/include/linux/limits.h b/include/linux/limits.h
> index b568b9c30bbf..f6bcc9369010 100644
> --- a/include/linux/limits.h
> +++ b/include/linux/limits.h
> @@ -7,6 +7,7 @@
>  #include <vdso/limits.h>
>  
>  #define SIZE_MAX	(~(size_t)0)
> +#define SSIZE_MAX	((ssize_t)(SIZE_MAX >> 1))
>  #define PHYS_ADDR_MAX	(~(phys_addr_t)0)
>  
>  #define U8_MAX		((u8)~0U)
> -- 
> 2.36.1.124.g0e6072fb45-goog
>