[PATCH] env: let setenv() take printf arguments

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

From: Sascha Hauer <s.hauer@pengutronix.de>

It's a common pattern to (ba)sprintf to a string and then call setenv()
with this string. Let setenv() take printf arguments to make that
easier. To avoid the overhead that goes with changing other callers
to using setenv(var, "%s", val) to avoid security implications (and
GCC warnings), fallback to the non-formatted version when there are
only two arguments.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
[afa: fall back to non-formatted version on old two arg version]
Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
---
Thoughts?
---
 common/env.c           | 37 +++++++++++++++++++++++++++++++++----
 include/environment.h  | 19 +++++++++++++++++--
 include/linux/kernel.h | 12 ++++++++++++
 3 files changed, 62 insertions(+), 6 deletions(-)

diff --git a/common/env.c b/common/env.c
index 05add63f625c..c36f6846ee21 100644
--- a/common/env.c
+++ b/common/env.c
@@ -243,15 +243,15 @@ static int dev_setenv(const char *name, const char *val)
 }
 
 /**
- * setenv - set environment variables
+ * __setenv_str - set environment variables
  * @_name - Variable name
  * @value - the value to set, empty string not handled specially
  *
  * Returns 0 for success and a negative error code otherwise
- * Use unsetenv() to unset.
+ * Use unsetenv() to unset. Don't use directly, use setenv()
  */
 
-int setenv(const char *_name, const char *value)
+int __setenv_str(const char *_name, const char *value)
 {
 	char *name = strdup(_name);
 	int ret = 0;
@@ -275,7 +275,36 @@ out:
 
 	return ret;
 }
-EXPORT_SYMBOL(setenv);
+EXPORT_SYMBOL(__setenv_str);
+
+/**
+ * __setenv_fmt - set environment variables
+ * @name - Variable name
+ * @fmt - format string describing how to format arguments to come
+ *
+ * Returns 0 for success and a negative error code otherwise
+ * Use unsetenv() to unset. Don't use directly, use setenv()
+ */
+
+int __setenv_fmt(const char *name, const char *fmt, ...)
+{
+	va_list ap;
+	int ret;
+	char *value;
+
+	va_start(ap, fmt);
+	ret = vasprintf(&value, fmt, ap);
+	va_end(ap);
+
+	if (ret < 0)
+		return ret;
+
+	ret = __setenv_str(name, value);
+
+	free(value);
+	return ret;
+}
+EXPORT_SYMBOL(__setenv_fmt);
 
 int export(const char *varname)
 {
diff --git a/include/environment.h b/include/environment.h
index 19e522cfb6b4..e5b9a9da3167 100644
--- a/include/environment.h
+++ b/include/environment.h
@@ -7,6 +7,7 @@
 #ifndef _ENVIRONMENT_H_
 #define _ENVIRONMENT_H_
 
+#include <linux/kernel.h>
 #include <linux/list.h>
 #include <errno.h>
 
@@ -31,7 +32,8 @@ char *var_name(struct variable_d *);
 
 #ifdef CONFIG_ENVIRONMENT_VARIABLES
 const char *getenv(const char *);
-int setenv(const char *, const char *);
+int __setenv_str(const char *, const char *val);
+int __setenv_fmt(const char *, const char *fmt, ...) __printf(2, 3);
 void export_env_ull(const char *name, unsigned long long val);
 int getenv_ull(const char *name, unsigned long long *val);
 int getenv_ul(const char *name, unsigned long *val);
@@ -44,7 +46,13 @@ static inline char *getenv(const char *var)
 	return NULL;
 }
 
-static inline int setenv(const char *var, const char *val)
+static inline int __setenv_str(const char *var, const char *val)
+{
+	return 0;
+}
+
+static inline __printf(2, 3) int __setenv_fmt(
+	const char *var, const char *fmt, ...)
 {
 	return 0;
 }
@@ -82,6 +90,13 @@ static inline const char *getenv_nonempty(const char *var)
 }
 #endif
 
+/*
+ * avoid the varargs overhead when using a fixed string
+ */
+#undef setenv
+#define setenv(args...) \
+	__optionally_variadic2(__setenv_str, __setenv_fmt, args)
+
 int env_pop_context(void);
 int env_push_context(void);
 
diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 4483d33e65bb..ebae8f666cf6 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -7,6 +7,7 @@
 #include <linux/barebox-wrapper.h>
 #include <linux/limits.h>
 #include <linux/math64.h>
+#include <linux/stringify.h>
 
 #define ALIGN(x, a)		__ALIGN_MASK(x, (typeof(x))(a) - 1)
 #define ALIGN_DOWN(x, a)	ALIGN((x) - ((a) - 1), (a))
@@ -17,6 +18,17 @@
 #define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]) + __must_be_array(arr))
 #define ARRAY_AND_SIZE(x)	(x), ARRAY_SIZE(x)
 
+/*
+ * Call func_variadic, when more than 2 arguments and func_fixed otherwise
+ */
+#define __optionally_variadic2(func_fixed, func_variadic, arg1, arg2, ...) ({ \
+		char _______STR[] = __stringify((__VA_ARGS__));  \
+		sizeof(_______STR) > 3 ?                         \
+			func_variadic(arg1, arg2, ##__VA_ARGS__) \
+		:                                                \
+			func_fixed(arg1, arg2);                  \
+	})
+
 /*
  * This looks more complex than it should be. But we need to
  * get the type for the ~ right in round_down (it needs to be
-- 
2.30.2