Re: [PATCH v2 09/18] fs/kernel_read_file: Switch buffer size arg to size_t

[Scott Branden <scott.branden@broadcom.com>]

works.

On 2020-07-22 12:30 p.m., Kees Cook wrote:
> In preparation for further refactoring of kernel_read_file*(), rename
> the "max_size" argument to the more accurate "buf_size", and correct
> its type to size_t. Add kerndoc to explain the specifics of how the
> arguments will be used. Note that with buf_size now size_t, it can no
> longer be negative (and was never called with a negative value). Adjust
> callers to use it as a "maximum size" when *buf is NULL.
>
> Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Scott Branden <scott.branden@broadcom.com>
> ---
>   fs/kernel_read_file.c            | 34 +++++++++++++++++++++++---------
>   include/linux/kernel_read_file.h |  8 ++++----
>   security/integrity/digsig.c      |  2 +-
>   security/integrity/ima/ima_fs.c  |  2 +-
>   4 files changed, 31 insertions(+), 15 deletions(-)
>
> diff --git a/fs/kernel_read_file.c b/fs/kernel_read_file.c
> index dc28a8def597..e21a76001fff 100644
> --- a/fs/kernel_read_file.c
> +++ b/fs/kernel_read_file.c
> @@ -5,15 +5,31 @@
>   #include <linux/security.h>
>   #include <linux/vmalloc.h>
>   
> +/**
> + * kernel_read_file() - read file contents into a kernel buffer
> + *
> + * @file	file to read from
> + * @buf		pointer to a "void *" buffer for reading into (if
> + *		*@buf is NULL, a buffer will be allocated, and
> + *		@buf_size will be ignored)
> + * @buf_size	size of buf, if already allocated. If @buf not
> + *		allocated, this is the largest size to allocate.
> + * @id		the kernel_read_file_id identifying the type of
> + *		file contents being read (for LSMs to examine)
> + *
> + * Returns number of bytes read (no single read will be bigger
> + * than INT_MAX), or negative on error.
> + *
> + */
>   int kernel_read_file(struct file *file, void **buf,
> -		     loff_t max_size, enum kernel_read_file_id id)
> +		     size_t buf_size, enum kernel_read_file_id id)
>   {
>   	loff_t i_size, pos;
>   	ssize_t bytes = 0;
>   	void *allocated = NULL;
>   	int ret;
>   
> -	if (!S_ISREG(file_inode(file)->i_mode) || max_size < 0)
> +	if (!S_ISREG(file_inode(file)->i_mode))
>   		return -EINVAL;
>   
>   	ret = deny_write_access(file);
> @@ -29,7 +45,7 @@ int kernel_read_file(struct file *file, void **buf,
>   		ret = -EINVAL;
>   		goto out;
>   	}
> -	if (i_size > INT_MAX || (max_size > 0 && i_size > max_size)) {
> +	if (i_size > INT_MAX || i_size > buf_size) {
>   		ret = -EFBIG;
>   		goto out;
>   	}
> @@ -75,7 +91,7 @@ int kernel_read_file(struct file *file, void **buf,
>   EXPORT_SYMBOL_GPL(kernel_read_file);
>   
>   int kernel_read_file_from_path(const char *path, void **buf,
> -			       loff_t max_size, enum kernel_read_file_id id)
> +			       size_t buf_size, enum kernel_read_file_id id)
>   {
>   	struct file *file;
>   	int ret;
> @@ -87,14 +103,14 @@ int kernel_read_file_from_path(const char *path, void **buf,
>   	if (IS_ERR(file))
>   		return PTR_ERR(file);
>   
> -	ret = kernel_read_file(file, buf, max_size, id);
> +	ret = kernel_read_file(file, buf, buf_size, id);
>   	fput(file);
>   	return ret;
>   }
>   EXPORT_SYMBOL_GPL(kernel_read_file_from_path);
>   
>   int kernel_read_file_from_path_initns(const char *path, void **buf,
> -				      loff_t max_size,
> +				      size_t buf_size,
>   				      enum kernel_read_file_id id)
>   {
>   	struct file *file;
> @@ -113,13 +129,13 @@ int kernel_read_file_from_path_initns(const char *path, void **buf,
>   	if (IS_ERR(file))
>   		return PTR_ERR(file);
>   
> -	ret = kernel_read_file(file, buf, max_size, id);
> +	ret = kernel_read_file(file, buf, buf_size, id);
>   	fput(file);
>   	return ret;
>   }
>   EXPORT_SYMBOL_GPL(kernel_read_file_from_path_initns);
>   
> -int kernel_read_file_from_fd(int fd, void **buf, loff_t max_size,
> +int kernel_read_file_from_fd(int fd, void **buf, size_t buf_size,
>   			     enum kernel_read_file_id id)
>   {
>   	struct fd f = fdget(fd);
> @@ -128,7 +144,7 @@ int kernel_read_file_from_fd(int fd, void **buf, loff_t max_size,
>   	if (!f.file)
>   		goto out;
>   
> -	ret = kernel_read_file(f.file, buf, max_size, id);
> +	ret = kernel_read_file(f.file, buf, buf_size, id);
>   out:
>   	fdput(f);
>   	return ret;
> diff --git a/include/linux/kernel_read_file.h b/include/linux/kernel_read_file.h
> index 0ca0bdbed1bd..910039e7593e 100644
> --- a/include/linux/kernel_read_file.h
> +++ b/include/linux/kernel_read_file.h
> @@ -36,16 +36,16 @@ static inline const char *kernel_read_file_id_str(enum kernel_read_file_id id)
>   }
>   
>   int kernel_read_file(struct file *file,
> -		     void **buf, loff_t max_size,
> +		     void **buf, size_t buf_size,
>   		     enum kernel_read_file_id id);
>   int kernel_read_file_from_path(const char *path,
> -			       void **buf, loff_t max_size,
> +			       void **buf, size_t buf_size,
>   			       enum kernel_read_file_id id);
>   int kernel_read_file_from_path_initns(const char *path,
> -				      void **buf, loff_t max_size,
> +				      void **buf, size_t buf_size,
>   				      enum kernel_read_file_id id);
>   int kernel_read_file_from_fd(int fd,
> -			     void **buf, loff_t max_size,
> +			     void **buf, size_t buf_size,
>   			     enum kernel_read_file_id id);
>   
>   #endif /* _LINUX_KERNEL_READ_FILE_H */
> diff --git a/security/integrity/digsig.c b/security/integrity/digsig.c
> index 97661ffabc4e..04f779c4f5ed 100644
> --- a/security/integrity/digsig.c
> +++ b/security/integrity/digsig.c
> @@ -175,7 +175,7 @@ int __init integrity_load_x509(const unsigned int id, const char *path)
>   	int rc;
>   	key_perm_t perm;
>   
> -	rc = kernel_read_file_from_path(path, &data, 0,
> +	rc = kernel_read_file_from_path(path, &data, INT_MAX,
>   					READING_X509_CERTIFICATE);
>   	if (rc < 0) {
>   		pr_err("Unable to open file: %s (%d)", path, rc);
> diff --git a/security/integrity/ima/ima_fs.c b/security/integrity/ima/ima_fs.c
> index 602f52717757..692b83e82edf 100644
> --- a/security/integrity/ima/ima_fs.c
> +++ b/security/integrity/ima/ima_fs.c
> @@ -284,7 +284,7 @@ static ssize_t ima_read_policy(char *path)
>   	datap = path;
>   	strsep(&datap, "\n");
>   
> -	rc = kernel_read_file_from_path(path, &data, 0, READING_POLICY);
> +	rc = kernel_read_file_from_path(path, &data, INT_MAX, READING_POLICY);
>   	if (rc < 0) {
>   		pr_err("Unable to open file: %s (%d)", path, rc);
>   		return rc;


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