linux-kernel - Re: [PATCH v2] fs: define a string representation of the kernel_read_file

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Message-ID: <CAGXu5j+7f=3_pCBE2-oJnn=2RH-B3ZLxhwi8XqxxvX9x+aZM2w@mail.gmail.com>
Date:	Wed, 20 Apr 2016 15:29:22 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Mimi Zohar <zohar@...ux.vnet.ibm.com>
Cc:	Al Viro <viro@...iv.linux.org.uk>,
	linux-security-module <linux-security-module@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH v2] fs: define a string representation of the
 kernel_read_file_id enumeration

On Mon, Apr 18, 2016 at 12:09 PM, Mimi Zohar <zohar@...ux.vnet.ibm.com> wrote:
> A string representation of the kernel_read_file_id enumeration is
> needed for displaying messages (eg. pr_info, auditing) that can be
> used by multiple LSMs and the integrity subsystem.  To simplify
> keeping the list of strings up to date with the enumeration, this
> patch defines two new preprocessing macros named __fid_enumify and
> __fid_stringify to create the enumeration and an array of strings.
> kernel_read_file_id_str() returns a string based on the enumeration.
>
> Changelog:
> - redefined the macros and simplified their usage - James Bottomley
>
> Signed-off-by: Mimi Zohar <zohar@...ux.vnet.ibm.com>

This works for me! I'll add it to my LSM series to replace my
implementation of kernel_read_file_id_str.

Thanks!

-Kees

> ---
>  fs/exec.c          | 19 -------------------
>  include/linux/fs.h | 32 +++++++++++++++++++++++++-------
>  2 files changed, 25 insertions(+), 26 deletions(-)
>
> diff --git a/fs/exec.c b/fs/exec.c
> index 05e71b6..c4010b8 100644
> --- a/fs/exec.c
> +++ b/fs/exec.c
> @@ -819,25 +819,6 @@ struct file *open_exec(const char *name)
>  }
>  EXPORT_SYMBOL(open_exec);
>
> -const char *kernel_read_file_id_str(enum kernel_read_file_id id)
> -{
> -       switch (id) {
> -       case READING_FIRMWARE:
> -               return "firmware";
> -       case READING_MODULE:
> -               return "kernel-module";
> -       case READING_KEXEC_IMAGE:
> -               return "kexec-image";
> -       case READING_KEXEC_INITRAMFS:
> -               return "kexec-initramfs";
> -       case READING_POLICY:
> -               return "security-policy";
> -       default:
> -               return "unknown";
> -       }
> -}
> -EXPORT_SYMBOL(kernel_read_file_id_str);
> -
>  int kernel_read(struct file *file, loff_t offset,
>                 char *addr, unsigned long count)
>  {
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 23ea886..497c17f 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -2580,16 +2580,34 @@ static inline void i_readcount_inc(struct inode *inode)
>  #endif
>  extern int do_pipe_flags(int *, int);
>
> +#define __kernel_read_file_id(id) \
> +       id(UNKNOWN, unknown)            \
> +       id(FIRMWARE, firmware)          \
> +       id(MODULE, kernel-module)               \
> +       id(KEXEC_IMAGE, kexec-image)            \
> +       id(KEXEC_INITRAMFS, kexec-initramfs)    \
> +       id(POLICY, security-policy)             \
> +       id(MAX_ID, )
> +
> +#define __fid_enumify(ENUM, dummy) READING_ ## ENUM,
> +#define __fid_stringify(dummy, str) #str,
> +
>  enum kernel_read_file_id {
> -       READING_FIRMWARE = 1,
> -       READING_MODULE,
> -       READING_KEXEC_IMAGE,
> -       READING_KEXEC_INITRAMFS,
> -       READING_POLICY,
> -       READING_MAX_ID
> +       __kernel_read_file_id(__fid_enumify)
> +};
> +
> +static const char *kernel_read_file_str[] = {
> +       __kernel_read_file_id(__fid_stringify)
>  };
>
> -extern const char *kernel_read_file_id_str(enum kernel_read_file_id id);
> +static inline const char *kernel_read_file_id_str(enum kernel_read_file_id id)
> +{
> +       if (id < 0 || id >= READING_MAX_ID)
> +               return kernel_read_file_str[READING_UNKNOWN];
> +
> +       return kernel_read_file_str[id];
> +}
> +
>  extern int kernel_read(struct file *, loff_t, char *, unsigned long);
>  extern int kernel_read_file(struct file *, void **, loff_t *, loff_t,
>                             enum kernel_read_file_id);
> --
> 2.1.0
>



-- 
Kees Cook
Chrome OS & Brillo Security