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

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Date:	Thu, 14 Apr 2016 16:49:12 -0400
From:	Mimi Zohar <zohar@...ux.vnet.ibm.com>
To:	Kees Cook <keescook@...omium.org>
Cc:	Al Viro <viro@...IV.linux.org.uk>,
	linux-security-module <linux-security-module@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: [RFC PATCH] fs: define a string representation of the
 kernel_read_file_id enumeration

(This patch is being posted as an RFC and has not been compiled.)

A string representation of the kernel_read_file_id enumeration is needed
for displaying messages (eg. pr_info, auditing).  We assume that the
string representation of the enumeration will be needed by multiple LSMs
and the integrity subsystem.  Instead of each defining their own string
representation, this patch defines a common one.

Each time a new enumeration entry is defined, it will need to be reflected
in the list of strings.  To simplify keeping the list of strings in sync
with the enumeration, this patch proposes using two preprocessing
macros: stringify_1 and an a new macro named enumify.

In general, preprocessing macros are not recommended.  The question is
whether using preprocessing macros is preferable to having to remember to
update the list each time a new enumeration is defined.

With these changes, the simplified version of kernel_read_file_id_str()
could be moved to a header.

Signed-off-by: Mimi Zohar <zohar@...ux.vnet.ibm.com>
---
 fs/exec.c          | 28 ++++++++++++++--------------
 include/linux/fs.h | 17 +++++++++++------
 2 files changed, 25 insertions(+), 20 deletions(-)

diff --git a/fs/exec.c b/fs/exec.c
index 05e71b6..e9b9b85 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -819,25 +819,25 @@ struct file *open_exec(const char *name)
 }
 EXPORT_SYMBOL(open_exec);
 
+static char *kernel_read_file_str[READING_MAX_ID];
 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";
-	}
+	return kernel_read_file_str[id];
 }
 EXPORT_SYMBOL(kernel_read_file_id_str);
 
+void __init kernel_read_file_init()
+{
+	const char *kernel_read_file_upper_str[] = {
+		 __kernel_read_file_id(__stringify_1)
+	};
+
+	for (i = 0; i < READING_MAX_ID; i++) {
+		kernel_read_file_str[i] = strdup(kernel_read_file_upper_str[i];
+		lower_case(kernel_read_file_str[i];
+	}
+}
+
 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..35ed80f 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2580,13 +2580,18 @@ 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)		\
+	id(FIRMWARE)		\
+	id(MODULE)		\
+	id(KEXEC_IMAGE)		\
+	id(KEXEC_INITRAMFS)	\
+	id(POLICY)		\
+	id(MAX_ID)		\
+#define __enumify(ENUM) READING_ ## ENUM,
+
 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(__enumify)
 };
 
 extern const char *kernel_read_file_id_str(enum kernel_read_file_id id);
-- 
2.1.0