[PATCH 7/9] Simplify string_escape_mem

["J. Bruce Fields" <bfields@redhat.com>]

From: "J. Bruce Fields" <bfields@redhat.com>

string_escape_mem is harder to use than necessary:

	- ESCAPE_NP sounds like it means "escape nonprinting
	  characters", but actually means "do not escape printing
	  characters"
	- the use of the "only" string to limit the list of escaped
	  characters rather than supplement them is confusing and
	  unehlpful.

So:

	- use the "only" string to add to, rather than replace, the list
	  of characters to escape
	- separate flags into those that select which characters to
	  escape, and those that choose the format of the escaping ("\ "
	  vs "\x20" vs "\040".)  Make flags that select characters just
	  select the union when they're OR'd together.

Untested.  The tests themselves, especially, I'm unsure about.

Signed-off-by: J. Bruce Fields <bfields@redhat.com>
---
 fs/proc/array.c                |  2 +-
 fs/seq_file.c                  |  2 +-
 include/linux/string_helpers.h | 14 +++----
 lib/string_helpers.c           | 76 +++++++++++++++-------------------
 lib/test-string_helpers.c      | 41 ++++++++----------
 lib/vsprintf.c                 |  2 +-
 net/sunrpc/cache.c             |  2 +-
 7 files changed, 62 insertions(+), 77 deletions(-)

diff --git a/fs/proc/array.c b/fs/proc/array.c
index 982c95d09176..bdeeb3318fa2 100644
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -111,7 +111,7 @@ void proc_task_name(struct seq_file *m, struct task_struct *p, bool escape)
 	size = seq_get_buf(m, &buf);
 	if (escape) {
 		ret = string_escape_str(tcomm, buf, size,
-					ESCAPE_SPECIAL, "\n\\");
+					ESCAPE_STYLE_SLASH, "\n\\");
 		if (ret >= size)
 			ret = -1;
 	} else {
diff --git a/fs/seq_file.c b/fs/seq_file.c
index 1600034a929b..63e5a7c4dbf7 100644
--- a/fs/seq_file.c
+++ b/fs/seq_file.c
@@ -379,7 +379,7 @@ void seq_escape(struct seq_file *m, const char *s, const char *esc)
 	size_t size = seq_get_buf(m, &buf);
 	int ret;
 
-	ret = string_escape_str(s, buf, size, ESCAPE_OCTAL, esc);
+	ret = string_escape_str(s, buf, size, ESCAPE_STYLE_OCTAL, esc);
 	seq_commit(m, ret < size ? ret : -1);
 }
 EXPORT_SYMBOL(seq_escape);
diff --git a/include/linux/string_helpers.h b/include/linux/string_helpers.h
index 7bf0d137373d..5d350f7f6874 100644
--- a/include/linux/string_helpers.h
+++ b/include/linux/string_helpers.h
@@ -41,13 +41,13 @@ static inline int string_unescape_any_inplace(char *buf)
 	return string_unescape_any(buf, buf, 0);
 }
 
-#define ESCAPE_SPECIAL		0x02
-#define ESCAPE_OCTAL		0x08
-#define ESCAPE_ANY		(ESCAPE_OCTAL | ESCAPE_SPECIAL)
-#define ESCAPE_NP		0x10
-#define ESCAPE_ANY_NP		(ESCAPE_ANY | ESCAPE_NP)
-#define ESCAPE_HEX		0x20
-#define ESCAPE_FLAG_MASK	0x3a
+#define ESCAPE_SPECIAL		0x01
+#define ESCAPE_NP		0x02
+#define ESCAPE_ANY_NP		(ESCAPE_SPECIAL | ESCAPE_NP)
+#define ESCAPE_STYLE_SLASH	0x20
+#define ESCAPE_STYLE_OCTAL	0x40
+#define ESCAPE_STYLE_HEX	0x80
+#define ESCAPE_FLAG_MASK	0xe3
 
 int string_escape_mem(const char *src, size_t isz, char *dst, size_t osz,
 		unsigned int flags, const char *only);
diff --git a/lib/string_helpers.c b/lib/string_helpers.c
index ac72159d3980..47f40406f9d4 100644
--- a/lib/string_helpers.c
+++ b/lib/string_helpers.c
@@ -400,6 +400,11 @@ static bool escape_hex(unsigned char c, char **dst, char *end)
 	return true;
 }
 
+static bool is_special(char c)
+{
+	return c == '\0' || strchr("\f\n\r\t\v\\\a\e", c);
+}
+
 /**
  * string_escape_mem - quote characters in the given memory buffer
  * @src:	source buffer (unescaped)
@@ -407,23 +412,18 @@ static bool escape_hex(unsigned char c, char **dst, char *end)
  * @dst:	destination buffer (escaped)
  * @osz:	destination buffer size
  * @flags:	combination of the flags
- * @only:	NULL-terminated string containing characters used to limit
- *		the selected escape class. If characters are included in @only
- *		that would not normally be escaped by the classes selected
- *		in @flags, they will be copied to @dst unescaped.
+ * @esc:	NULL-terminated string containing characters which
+ *		should also be escaped.
  *
- * Description:
- * The process of escaping byte buffer includes several parts. They are applied
- * in the following sequence.
  *
- *	1. The character is matched to the printable class, if asked, and in
- *	   case of match it passes through to the output.
- *	2. The character is not matched to the one from @only string and thus
- *	   must go as-is to the output.
- *	3. The character is checked if it falls into the class given by @flags.
- *	   %ESCAPE_OCTAL and %ESCAPE_HEX are going last since they cover any
- *	   character. Note that they actually can't go together, otherwise
- *	   %ESCAPE_HEX will be ignored.
+ * Description:
+ * The characters selected by ESCAPE_* flags and by the "esc" string
+ * are escaped, using the escaping specified by the ESCAPE_STYLE_*
+ * flags.  If ESCAPE_STYLE_SLASH is specified together with one of the
+ * ESCAPE_STYLE_OCTAL or ESCAPE_STYLE_HEX flags, then those characters
+ * for which special slash escapes exist will be escaped using those,
+ * with others escaped using octal or hexidecimal values.  If
+ * unspecified, the default is ESCAPE_STYLE_OCTAL.
  *
  * Caller must provide valid source and destination pointers. Be aware that
  * destination buffer will not be NULL-terminated, thus caller have to append
@@ -439,14 +439,14 @@ static bool escape_hex(unsigned char c, char **dst, char *end)
  *		'\a' - alert (BEL)
  *		'\e' - escape
  *		'\0' - null
- *	%ESCAPE_OCTAL:
- *		'\NNN' - byte with octal value NNN (3 digits)
- *	%ESCAPE_ANY:
- *		all previous together
  *	%ESCAPE_NP:
  *		escape only non-printable characters (checked by isprint)
  *	%ESCAPE_ANY_NP:
  *		all previous together
+ *	%ESCAPE_STYLE_SLASH:
+ *		Escape using the slash codes shown above
+ *	%ESCAPE_STYLE_OCTAL:
+ *		'\NNN' - byte with octal value NNN (3 digits)
  *	%ESCAPE_HEX:
  *		'\xHH' - byte with hexadecimal value HH (2 digits)
  *
@@ -457,39 +457,31 @@ static bool escape_hex(unsigned char c, char **dst, char *end)
  * dst for a '\0' terminator if and only if ret < osz.
  */
 int string_escape_mem(const char *src, size_t isz, char *dst, size_t osz,
-		      unsigned int flags, const char *only)
+		      unsigned int flags, const char *esc)
 {
 	char *p = dst;
 	char *end = p + osz;
-	bool is_dict = only && *only;
+	bool is_dict = esc && *esc;
 
 	while (isz--) {
 		unsigned char c = *src++;
 
-		/*
-		 * Apply rules in the following sequence:
-		 *	- the character is printable, when @flags has
-		 *	  %ESCAPE_NP bit set
-		 *	- the @only string is supplied and does not contain a
-		 *	  character under question
-		 *	- the character doesn't fall into a class of symbols
-		 *	  defined by given @flags
-		 * In these cases we just pass through a character to the
-		 * output buffer.
-		 */
-		if ((flags & ESCAPE_NP && isprint(c)) ||
-		    (is_dict && !strchr(only, c))) {
-			/* do nothing */
-		} else {
-			if (flags & ESCAPE_SPECIAL && escape_special(c, &p, end))
-				continue;
+		if ((is_dict && strchr(esc, c)) ||
+		    (flags & ESCAPE_NP && !isprint(c)) ||
+		    (flags & ESCAPE_SPECIAL && is_special(c))) {
 
-			/* ESCAPE_OCTAL and ESCAPE_HEX always go last */
-			if (flags & ESCAPE_OCTAL && escape_octal(c, &p, end))
+			if (flags & ESCAPE_STYLE_SLASH &&
+					escape_special(c, &p, end))
 				continue;
 
-			if (flags & ESCAPE_HEX && escape_hex(c, &p, end))
+			if (flags & ESCAPE_STYLE_HEX &&
+					escape_hex(c, &p, end))
 				continue;
+			/*
+			 * Always the default, so a caller doesn't
+			 * accidentally leave something unescaped:
+			 */
+			escape_octal(c, &p, end);
 		}
 
 		escape_passthrough(c, &p, end);
@@ -526,7 +518,7 @@ char *kstrdup_quotable(const char *src, gfp_t gfp)
 {
 	size_t slen, dlen;
 	char *dst;
-	const int flags = ESCAPE_HEX;
+	const int flags = ESCAPE_STYLE_HEX;
 	const char esc[] = "\f\n\r\t\v\a\e\\\"";
 
 	if (!src)
diff --git a/lib/test-string_helpers.c b/lib/test-string_helpers.c
index 0da3c195a327..d40fedab24ad 100644
--- a/lib/test-string_helpers.c
+++ b/lib/test-string_helpers.c
@@ -127,13 +127,13 @@ static const struct test_string_2 escape0[] __initconst = {{
 	.in = "\\h\\\"\a\e\\",
 	.s1 = {{
 		.out = "\\\\h\\\\\"\\a\\e\\\\",
-		.flags = ESCAPE_SPECIAL,
+		.flags = ESCAPE_SPECIAL | ESCAPE_STYLE_SLASH,
 	},{
 		.out = "\\\\\\150\\\\\\042\\a\\e\\\\",
-		.flags = ESCAPE_SPECIAL | ESCAPE_OCTAL,
+		.flags = ESCAPE_SPECIAL | ESCAPE_STYLE_SLASH | ESCAPE_STYLE_OCTAL,
 	},{
 		.out = "\\\\\\x68\\\\\\x22\\a\\e\\\\",
-		.flags = ESCAPE_SPECIAL | ESCAPE_HEX,
+		.flags = ESCAPE_SPECIAL | ESCAPE_STYLE_SLASH | ESCAPE_STYLE_HEX,
 	},{
 		/* terminator */
 	}},
@@ -141,28 +141,19 @@ static const struct test_string_2 escape0[] __initconst = {{
 	.in = "\eb \\C\007\"\x90\r]",
 	.s1 = {{
 		.out = "\\eb \\\\C\\a\"\x90\\r]",
-		.flags = ESCAPE_SPECIAL,
-	},{
-		.out = "\\033\\142\\040\\134\\103\\007\\042\\220\\015\\135",
-		.flags = ESCAPE_OCTAL,
+		.flags = ESCAPE_SPECIAL | ESCAPE_STYLE_SLASH,
 	},{
 		.out = "\\e\\142\\040\\\\\\103\\a\\042\\220\\r\\135",
-		.flags = ESCAPE_SPECIAL | ESCAPE_OCTAL,
-	},{
-		.out = "\eb \\C\007\"\x90\r]",
-		.flags = ESCAPE_NP,
+		.flags = ESCAPE_SPECIAL | ESCAPE_STYLE_SLASH | ESCAPE_STYLE_OCTAL,
 	},{
 		.out = "\\eb \\C\\a\"\x90\\r]",
-		.flags = ESCAPE_SPECIAL | ESCAPE_NP,
-	},{
-		.out = "\\033b \\C\\007\"\\220\\015]",
-		.flags = ESCAPE_OCTAL | ESCAPE_NP,
+		.flags = ESCAPE_SPECIAL | ESCAPE_STYLE_SLASH | ESCAPE_STYLE_OCTAL,
 	},{
 		.out = "\\eb \\C\\a\"\\220\\r]",
-		.flags = ESCAPE_SPECIAL ESCAPE_OCTAL | ESCAPE_NP,
+		.flags = ESCAPE_SPECIAL | ESCAPE_STYLE_OCTAL | ESCAPE_NP,
 	},{
 		.out = "\\x1bb \\C\\x07\"\\x90\\x0d]",
-		.flags = ESCAPE_NP | ESCAPE_HEX,
+		.flags = ESCAPE_NP | ESCAPE_STYLE_HEX,
 	},{
 		/* terminator */
 	}},
@@ -175,10 +166,10 @@ static const struct test_string_2 escape1[] __initconst = {{
 	.in = "\f\\ \n\r\t\v",
 	.s1 = {{
 		.out = "\f\\134\\040\n\\015\\011\v",
-		.flags = ESCAPE_OCTAL,
+		.flags = ESCAPE_STYLE_OCTAL,
 	},{
 		.out = "\f\\x5c\\x20\n\\x0d\\x09\v",
-		.flags = ESCAPE_HEX,
+		.flags = ESCAPE_STYLE_HEX,
 	},{
 		/* terminator */
 	}},
@@ -186,7 +177,7 @@ static const struct test_string_2 escape1[] __initconst = {{
 	.in = "\\h\\\"\a\e\\",
 	.s1 = {{
 		.out = "\\134h\\134\"\a\e\\134",
-		.flags = ESCAPE_OCTAL,
+		.flags = ESCAPE_STYLE_OCTAL,
 	},{
 		/* terminator */
 	}},
@@ -194,7 +185,7 @@ static const struct test_string_2 escape1[] __initconst = {{
 	.in = "\eb \\C\007\"\x90\r]",
 	.s1 = {{
 		.out = "\e\\142\\040\\134C\007\"\x90\\015]",
-		.flags = ESCAPE_OCTAL,
+		.flags = ESCAPE_STYLE_OCTAL,
 	},{
 		/* terminator */
 	}},
@@ -211,9 +202,9 @@ static __init const char *test_string_find_match(const struct test_string_2 *s2,
 	if (!flags)
 		return s2->in;
 
-	/* ESCAPE_OCTAL has a higher priority */
-	if (flags & ESCAPE_OCTAL)
-		flags &= ~ESCAPE_HEX;
+	/* ESCAPE_OCTAL is default: */
+	if (!(flags & ESCAPE_STYLE_HEX))
+		flags |= ESCAPE_STYLE_OCTAL;
 
 	for (i = 0; i < TEST_STRING_2_MAX_S1 && s1->out; i++, s1++)
 		if (s1->flags == flags)
@@ -266,6 +257,8 @@ static __init void test_string_escape(const char *name,
 		memcpy(&out_test[q_test], out, len);
 		q_test += len;
 	}
+	if (!p)
+		goto out;
 
 	q_real = string_escape_mem(in, p, out_real, out_size, flags, esc);
 
diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 5522d2a052e1..020aff0c3fd9 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -1553,7 +1553,7 @@ char *escaped_string(char *buf, char *end, u8 *addr, struct printf_spec spec,
 	 * had the buffer been big enough.
 	 */
 	buf += string_escape_mem(addr, len, buf, buf < end ? end - buf : 0,
-				 ESCAPE_ANY_NP, NULL);
+				 ESCAPE_ANY_NP|ESCAPE_STYLE_SLASH, NULL);
 
 	return buf;
 }
diff --git a/net/sunrpc/cache.c b/net/sunrpc/cache.c
index 6f1528f271ee..1b5a2b9e7808 100644
--- a/net/sunrpc/cache.c
+++ b/net/sunrpc/cache.c
@@ -1118,7 +1118,7 @@ void qword_add(char **bpp, int *lp, char *str)
 
 	if (len < 0) return;
 
-	ret = string_escape_str(str, bp, len, ESCAPE_OCTAL, "\\ \n\t");
+	ret = string_escape_str(str, bp, len, ESCAPE_STYLE_OCTAL, "\\ \n\t");
 	if (ret >= len) {
 		bp += len;
 		len = -1;
-- 
2.21.0