ifcfg-rh: restore previous behavior for svUnescape() stripping backslash from double-quoting

Now we could parse simple shell variable assignment properly, but old versions
of svEscape() wrote invalid double-quoted strings.

Add a hack to restore the broken behavior for that case only.

src/settings/plugins/ifcfg-rh/shvar.c

@@ -245,6 +245,28 @@ svEscape (const char *s, char **to_free)
 	return new;
 }
 
+static gboolean
+_looks_like_old_svescaped (const char *value)
+{
+	gsize k;
+
+	if (value[0] != '"')
+		return FALSE;
+
+	for (k = 1; ; k++) {
+		if (value[k] == '\0')
+			return FALSE;
+		if (value[k] == '"')
+			return (value[k + 1] == '\0');
+		if (value[k] == '\\') {
+			k++;
+			if (!_char_in_strset (value[k], "\"'\\$~`"))
+				return FALSE;
+		} else if (_char_in_strset (value[k], "'\\$~`"))
+			return FALSE;
+	}
+}
+
 static gboolean
 _ch_octal_is (char ch)
 {
@@ -302,6 +324,7 @@ svUnescape (const char *value, char **to_free)
 {
 	gsize i, j;
 	nm_auto_free_gstring GString *str = NULL;
+	int looks_like_old_svescaped = -1;
 
 	/* we handle bash syntax here (note that ifup has #!/bin/bash.
 	 * Thus, see https://www.gnu.org/software/bash/manual/html_node/Quoting.html#Quoting */
@@ -404,7 +427,26 @@ svUnescape (const char *value, char **to_free)
 						/* we don't support line continuation */
 						goto out_error;
 					}
-					if (!NM_IN_SET (value[i], '$', '`', '"', '\\'))
+					if (NM_IN_SET (value[i], '$', '`', '"', '\\')) {
+						/* Drop the backslash. */
+					} else if (NM_IN_SET (value[i], '\'', '~')) {
+						/* '\'' and '~' in double qoutes are not handled special by shell.
+						 * However, old versions of svEscape() would wrongly use double-quoting
+						 * with backslash escaping for these characters (expecting svUnescape()
+						 * to remove the backslash).
+						 *
+						 * In order to preserve previous behavior, we continue to read such
+						 * strings different then shell does. */
+
+						/* Actually, we can relax this. Old svEscape() escaped the entire value
+						 * in a particular way with double quotes.
+						 * If the value doesn't exactly look like something as created by svEscape(),
+						 * don't do the compat hack and preserve the backslash. */
+						if (looks_like_old_svescaped < 0)
+							looks_like_old_svescaped = _looks_like_old_svescaped (value);
+						if (!looks_like_old_svescaped)
+							g_string_append_c (str, '\\');
+					} else
 						g_string_append_c (str, '\\');
 				}
 				g_string_append_c (str, value[i]);

src/settings/plugins/ifcfg-rh/tests/test-ifcfg-rh.c

@@ -8233,8 +8233,6 @@ test_svUnescape (void)
 		V1 ("\"\\\\\"", "\\"),
 		V1 ("\"\\a\"", "\\a"),
 		V1 ("\"\\b\"", "\\b"),
-		V1 ("\"\\'\"", "\\'"),
-		V1 ("\"\\~\"", "\\~"),
 		V1 ("\"\\\t\"", "\\\t"),
 		V0 ("ab\r", "ab"),
 		V0 ("a'b'\r ", "ab"),
@@ -8262,6 +8260,23 @@ test_svUnescape (void)
 		V1 ("\"aa\\\"\"", "aa\""),
 		V1 ("\"aa\\\"b\"c", "aa\"bc"),
 		V1 ("\"aa\\\"\"b", "aa\"b"),
+
+		/* the following is not shell behavior, but kept for backward compatibility
+		 * with old svEscape(). */
+		V0 ("\"\\'\"", "'"),
+		V0 ("\"\\~\"", "~"),
+		V0 ("\"b\\~b\"", "b~b"),
+		V0 ("\"\\~\\~\"", "~~"),
+		V0 ("\"\\~\\'\"", "~'"),
+
+		/* the following is shell-behavior, because it doesn't look like written
+		 * by old svEscape(). */
+		V1 ("\"\\~~\"", "\\~~"),
+		V1 ("\"\\a\\'\"", "\\a\\'"),
+		V1 ("x\"\\~\"", "x\\~"),
+		V1 ("\"\\'\"''", "\\'"),
+		V0 ("\"b\\~b\" ", "b\\~b"),
+		V1 ("\"b\\~b\"x", "b\\~bx"),
 	};
 	const UnescapeTestData data_ansi[] = {
 		/* strings inside $''. They cannot be compared directly, but must