[PATCH 3/4] Add strict version of vsscanf()

[Demi Marie Obenour <demi@invisiblethingslab.com>]

Signed-off-by: Demi Marie Obenour <demi@invisiblethingslab.com>
---
 include/linux/kernel.h |  4 ++++
 lib/vsprintf.c         | 43 +++++++++++++++++++++++++++++++++++++++---
 2 files changed, 44 insertions(+), 3 deletions(-)

diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 0d91e0af01250c1d82f4a2ea562d2619b9cc6e9c..b348b84ce9c4e95031f67e0cbac5de8deca69aac 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -227,8 +227,12 @@ const char *kvasprintf_const(gfp_t gfp, const char *fmt, va_list args);
 
 extern __scanf(2, 3)
 int sscanf(const char *, const char *, ...);
+extern __scanf(2, 3)
+int sscanf_strict(const char *, const char *, ...);
 extern __scanf(2, 0)
 int vsscanf(const char *, const char *, va_list);
+extern __scanf(2, 0)
+int vsscanf_strict(const char *, const char *, va_list);
 
 extern int no_hash_pointers_enable(char *str);
 
diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 9846d2385f5b9e8f3945a5664d81047e97cf10d5..2dae357b367e1da8b1004ed6e85e051a045ca36b 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -3414,6 +3414,8 @@ EXPORT_SYMBOL_GPL(bprintf);
 
 #endif /* CONFIG_BINARY_PRINTF */
 
+static int vsscanf_internal(const char *buf, const char *fmt, va_list args, bool strict);
+
 /**
  * vsscanf - Unformat a buffer into a list of arguments
  * @buf:	input buffer
@@ -3421,6 +3423,23 @@ EXPORT_SYMBOL_GPL(bprintf);
  * @args:	arguments
  */
 int vsscanf(const char *buf, const char *fmt, va_list args)
+{
+	return vsscanf_internal(buf, fmt, args, false);
+}
+
+/**
+ * vsscanf_strict - Unformat a buffer into a list of arguments, but
+ *                  do not skip spaces.
+ * @buf:	input buffer
+ * @fmt:	format of buffer
+ * @args:	arguments
+ */
+int vsscanf_strict(const char *buf, const char *fmt, va_list args)
+{
+	return vsscanf_internal(buf, fmt, args, true);
+}
+
+static int vsscanf_internal(const char *buf, const char *fmt, va_list args, bool strict)
 {
 	const char *str = buf;
 	char *next;
@@ -3530,8 +3549,10 @@ int vsscanf(const char *buf, const char *fmt, va_list args)
 			char *s = (char *)va_arg(args, char *);
 			if (field_width == -1)
 				field_width = SHRT_MAX;
-			/* first, skip leading white space in buffer */
-			str = skip_spaces(str);
+			if (!strict) {
+				/* first, skip leading white space in buffer */
+				str = skip_spaces(str);
+			}
 
 			/* now copy until next white space */
 			while (*str && !isspace(*str) && field_width--)
@@ -3621,7 +3642,8 @@ int vsscanf(const char *buf, const char *fmt, va_list args)
 		/* have some sort of integer conversion.
 		 * first, skip white space in buffer.
 		 */
-		str = skip_spaces(str);
+		if (!strict)
+			str = skip_spaces(str);
 
 		digit = *str;
 		if (is_sign && digit == '-') {
@@ -3721,6 +3743,9 @@ int vsscanf(const char *buf, const char *fmt, va_list args)
 		str = next;
 	}
 
+	if (strict && *str)
+		return -EINVAL;
+
 	return num;
 }
 EXPORT_SYMBOL(vsscanf);
@@ -3743,3 +3768,15 @@ int sscanf(const char *buf, const char *fmt, ...)
 	return i;
 }
 EXPORT_SYMBOL(sscanf);
+int sscanf_strict(const char *buf, const char *fmt, ...)
+{
+	va_list args;
+	int i;
+
+	va_start(args, fmt);
+	i = vsscanf_strict(buf, fmt, args);
+	va_end(args);
+
+	return i;
+}
+EXPORT_SYMBOL(sscanf_strict);
-- 
Sincerely,
Demi Marie Obenour (she/her/hers)
Invisible Things Lab