[PATCH] snprintf fixes

From: Juergen Quade <quade@hsnr.de>

Lots of places in the kernel are using [v]snprintf wrongly: they assume it
returns the number of characters copied.  It doesn't.  It returns the
number of characters which _would_ have been copied had the buffer not been
filled up.

So create new functions vscnprintf() and scnprintf() which have the
expected (sane) semaptics, and migrate callers over to using them.

1 files changed, 74 insertions, 13 deletions

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index b30a4a2541c0..b6d283372cf5 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -12,6 +12,8 @@
 /* 
  * Fri Jul 13 2001 Crutcher Dunnavant <crutcher+kernel@datastacks.com>
  * - changed to provide snprintf and vsnprintf functions
+ * So Feb  1 16:51:32 CET 2004 Juergen Quade <quade@hsnr.de>
+ * - scnprintf and vscnprintf
  */
 
 #include <stdarg.h>
@@ -228,19 +230,22 @@ static char * number(char * buf, char * end, unsigned long long num, int base, i
 }
 
 /**
-* vsnprintf - Format a string and place it in a buffer
-* @buf: The buffer to place the result into
-* @size: The size of the buffer, including the trailing null space
-* @fmt: The format string to use
-* @args: Arguments for the format string
-*
-* The return value is the number of characters which would be
-* generated for the given input, excluding the trailing null,
-* as per ISO C99.  If the return is greater than or equal to
-* @size, the resulting string is truncated.
-*
-* Call this function if you are already dealing with a va_list.
-* You probably want snprintf instead.
+ * vsnprintf - Format a string and place it in a buffer
+ * @buf: The buffer to place the result into
+ * @size: The size of the buffer, including the trailing null space
+ * @fmt: The format string to use
+ * @args: Arguments for the format string
+ *
+ * The return value is the number of characters which would
+ * be generated for the given input, excluding the trailing
+ * '\0', as per ISO C99. If you want to have the exact
+ * number of characters written into @buf as return value
+ * (not including the trailing '\0'), use vscnprintf. If the
+ * return is greater than or equal to @size, the resulting
+ * string is truncated.
+ *
+ * Call this function if you are already dealing with a va_list.
+ * You probably want snprintf instead.
  */
 int vsnprintf(char *buf, size_t size, const char *fmt, va_list args)
 {
@@ -482,6 +487,30 @@ int vsnprintf(char *buf, size_t size, const char *fmt, va_list args)
 EXPORT_SYMBOL(vsnprintf);
 
 /**
+ * vscnprintf - Format a string and place it in a buffer
+ * @buf: The buffer to place the result into
+ * @size: The size of the buffer, including the trailing null space
+ * @fmt: The format string to use
+ * @args: Arguments for the format string
+ *
+ * The return value is the number of characters which have been written into
+ * the @buf not including the trailing '\0'. If @size is <= 0 the function
+ * returns 0.
+ *
+ * Call this function if you are already dealing with a va_list.
+ * You probably want scnprintf instead.
+ */
+int vscnprintf(char *buf, size_t size, const char *fmt, va_list args)
+{
+	int i;
+
+	i=vsnprintf(buf,size,fmt,args);
+	return (i >= size) ? (size - 1) : i;
+}
+
+EXPORT_SYMBOL(vscnprintf);
+
+/**
  * snprintf - Format a string and place it in a buffer
  * @buf: The buffer to place the result into
  * @size: The size of the buffer, including the trailing null space
@@ -507,11 +536,39 @@ int snprintf(char * buf, size_t size, const char *fmt, ...)
 EXPORT_SYMBOL(snprintf);
 
 /**
+ * scnprintf - Format a string and place it in a buffer
+ * @buf: The buffer to place the result into
+ * @size: The size of the buffer, including the trailing null space
+ * @fmt: The format string to use
+ * @...: Arguments for the format string
+ *
+ * The return value is the number of characters written into @buf not including
+ * the trailing '\0'. If @size is <= 0 the function returns 0. If the return is
+ * greater than or equal to @size, the resulting string is truncated.
+ */
+
+int scnprintf(char * buf, size_t size, const char *fmt, ...)
+{
+	va_list args;
+	int i;
+
+	va_start(args, fmt);
+	i = vsnprintf(buf, size, fmt, args);
+	va_end(args);
+	return (i >= size) ? (size - 1) : i;
+}
+EXPORT_SYMBOL(scnprintf);
+
+/**
  * vsprintf - Format a string and place it in a buffer
  * @buf: The buffer to place the result into
  * @fmt: The format string to use
  * @args: Arguments for the format string
  *
+ * The function returns the number of characters written
+ * into @buf. Use vsnprintf or vscnprintf in order to avoid
+ * buffer overflows.
+ *
  * Call this function if you are already dealing with a va_list.
  * You probably want sprintf instead.
  */
@@ -527,6 +584,10 @@ EXPORT_SYMBOL(vsprintf);
  * @buf: The buffer to place the result into
  * @fmt: The format string to use
  * @...: Arguments for the format string
+ *
+ * The function returns the number of characters written
+ * into @buf. Use snprintf or scnprintf in order to avoid
+ * buffer overflows.
  */
 int sprintf(char * buf, const char *fmt, ...)
 {