lib/string_helpers: introduce generic string_unescape

There are several places in kernel where modules unescapes input to convert
C-Style Escape Sequences into byte codes.

The patch provides generic implementation of such approach. Test cases are
also included into the patch.

[akpm@linux-foundation.org: clarify comment]
[akpm@linux-foundation.org: export get_random_int() to modules]
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Samuel Thibault <samuel.thibault@ens-lyon.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jason Baron <jbaron@redhat.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: William Hubbs <w.d.hubbs@gmail.com>
Cc: Chris Brannon <chris@the-brannons.com>
Cc: Kirk Reiser <kirk@braille.uwo.ca>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 133 insertions, 0 deletions

diff --git a/lib/string_helpers.c b/lib/string_helpers.c
index 1cffc22..ed5c145 100644
--- a/lib/string_helpers.c
+++ b/lib/string_helpers.c
@@ -2,10 +2,12 @@
  * Helpers for formatting and printing strings
  *
  * Copyright 31 August 2008 James Bottomley
+ * Copyright (C) 2013, Intel Corporation
  */
 #include <linux/kernel.h>
 #include <linux/math64.h>
 #include <linux/export.h>
+#include <linux/ctype.h>
 #include <linux/string_helpers.h>
 
 /**
@@ -66,3 +68,134 @@ int string_get_size(u64 size, const enum string_size_units units,
 	return 0;
 }
 EXPORT_SYMBOL(string_get_size);
+
+static bool unescape_space(char **src, char **dst)
+{
+	char *p = *dst, *q = *src;
+
+	switch (*q) {
+	case 'n':
+		*p = '\n';
+		break;
+	case 'r':
+		*p = '\r';
+		break;
+	case 't':
+		*p = '\t';
+		break;
+	case 'v':
+		*p = '\v';
+		break;
+	case 'f':
+		*p = '\f';
+		break;
+	default:
+		return false;
+	}
+	*dst += 1;
+	*src += 1;
+	return true;
+}
+
+static bool unescape_octal(char **src, char **dst)
+{
+	char *p = *dst, *q = *src;
+	u8 num;
+
+	if (isodigit(*q) == 0)
+		return false;
+
+	num = (*q++) & 7;
+	while (num < 32 && isodigit(*q) && (q - *src < 3)) {
+		num <<= 3;
+		num += (*q++) & 7;
+	}
+	*p = num;
+	*dst += 1;
+	*src = q;
+	return true;
+}
+
+static bool unescape_hex(char **src, char **dst)
+{
+	char *p = *dst, *q = *src;
+	int digit;
+	u8 num;
+
+	if (*q++ != 'x')
+		return false;
+
+	num = digit = hex_to_bin(*q++);
+	if (digit < 0)
+		return false;
+
+	digit = hex_to_bin(*q);
+	if (digit >= 0) {
+		q++;
+		num = (num << 4) | digit;
+	}
+	*p = num;
+	*dst += 1;
+	*src = q;
+	return true;
+}
+
+static bool unescape_special(char **src, char **dst)
+{
+	char *p = *dst, *q = *src;
+
+	switch (*q) {
+	case '\"':
+		*p = '\"';
+		break;
+	case '\\':
+		*p = '\\';
+		break;
+	case 'a':
+		*p = '\a';
+		break;
+	case 'e':
+		*p = '\e';
+		break;
+	default:
+		return false;
+	}
+	*dst += 1;
+	*src += 1;
+	return true;
+}
+
+int string_unescape(char *src, char *dst, size_t size, unsigned int flags)
+{
+	char *out = dst;
+
+	while (*src && --size) {
+		if (src[0] == '\\' && src[1] != '\0' && size > 1) {
+			src++;
+			size--;
+
+			if (flags & UNESCAPE_SPACE &&
+					unescape_space(&src, &out))
+				continue;
+
+			if (flags & UNESCAPE_OCTAL &&
+					unescape_octal(&src, &out))
+				continue;
+
+			if (flags & UNESCAPE_HEX &&
+					unescape_hex(&src, &out))
+				continue;
+
+			if (flags & UNESCAPE_SPECIAL &&
+					unescape_special(&src, &out))
+				continue;
+
+			*out++ = '\\';
+		}
+		*out++ = *src++;
+	}
+	*out = '\0';
+
+	return out - dst;
+}
+EXPORT_SYMBOL(string_unescape);