fix: escape control characters in IfcfgUtil.ValueEscape

The ANSI-C quoting branch tested `ord(c) < ord(c)`, which is always
False, so the escaping path was dead and control characters were
written raw into the $'...' string. ifcfg_to_content() emits one
KEY=VALUE per line, so a value containing a newline broke that
structure in the generated file.

The escape also emitted a decimal code point, but ANSI-C quoting
reads \nnn as octal, so the sequence would have decoded to the wrong
character once the branch became reachable. Both are corrected by
comparing against ord(" ") and emitting %03o.

Adds unit tests covering the ANSI-C path, the double-quoting path and
the unquoted path. The two control-character tests fail without the
fix.

Documents the escaping rules in the ValueEscape docstring, citing
Bash Reference Manual 3.1.2.3 and 3.1.2.4.

Signed-off-by: Suraj Patil <surajpatil522@gmail.com>

Author: suraj-cmd

library/network_connections.py

@@ -301,7 +301,23 @@ def KeyValid(cls, name):
 
     @classmethod
     def ValueEscape(cls, value):
-
+        """Quote a value for an ifcfg file, which is shell syntax.
+
+        Two quoting styles are produced, matching the Bash Reference
+        Manual:
+
+        ANSI-C quoting, $'...', used when the value contains control
+        characters (Bash Reference Manual 3.1.2.4). Backslash escapes
+        are decoded per the ANSI C standard, so \\nnn is the eight-bit
+        character whose value is the *octal* value nnn, one to three
+        octal digits. Backslash and single quote are escaped with a
+        preceding backslash.
+
+        Double quoting, "...", used otherwise (Bash Reference Manual
+        3.1.2.3). Within double quotes the characters $, `, \\ and "
+        retain their special meaning and are escaped with a preceding
+        backslash.
+        """
         r = getattr(cls, "_re_ValueEscape", None)
         if r is None:
             r = re.compile("^[a-zA-Z_0-9-.]*$")
@@ -314,8 +330,8 @@ def ValueEscape(cls, value):
             # needs ansic escaping due to ANSI control characters (newline)
             s = "$'"
             for c in value:
-                if ord(c) < ord(c):
-                    s += "\\" + str(ord(c))
+                if ord(c) < ord(" "):
+                    s += "\\%03o" % ord(c)
                 elif c == "\\" or c == "'":
                     s += "\\" + c
                 else:

tests/unit/test_network_connections.py

@@ -5657,5 +5657,19 @@ def unstable_fetch():
         self.assertEqual(fetch_mock.call_count, 51)
 
 
+class TestIfcfgUtilValueEscape(unittest.TestCase):
+    def test_plain_value_is_not_quoted(self):
+        self.assertEqual(IfcfgUtil.ValueEscape("eth0"), "eth0")
+
+    def test_control_char_escaped_as_octal(self):
+        self.assertEqual(IfcfgUtil.ValueEscape("line1\nline2"), "$'line1\\012line2'")
+
+    def test_control_char_with_quote_and_backslash(self):
+        self.assertEqual(IfcfgUtil.ValueEscape("a\n'b\\c"), "$'a\\012\\'b\\\\c'")
+
+    def test_double_quoting_path_is_unchanged(self):
+        self.assertEqual(IfcfgUtil.ValueEscape('a "b" $c'), '"a \\"b\\" \\$c"')
+
+
 if __name__ == "__main__":
     unittest.main()