Merged PR 5078953: Work around Sexp crate issue with handling quotes

Work around Sexp crate issue with handling quotes

The sexp crate has a bug around handling quoted strings that makes it
impossible to differentiate between a quoted and an unquoted string.

cgaebel/sexp#2

The short version is that quotes are added on output strings based on
heuristics that include the presence of quotes in the original string,
so giving a quoted string to sexp yields a doubly quoted string, and
giving an unquoted string yields an unquoted string, resulting in no
way to generate a Sexp structure that will output a quoted string with
the Display trait, unless that string meets one of the following
criteria:

1. Contains a quote
2. Contains whitespace
3. Is a number

For CIL filecon statements, we need to include quoted strings, which
meet none of these criteria.

The sexp crate project appears to be abandoned, so a PR will not be
fruitful.  Rather than higher level of effort approaches such as forking
the project or migrating to a different sexp crate, this commit simply
works around the issue by adding a simple new display function that does
no quote special handling.  This requires us to manage quotes
internally, but that's really what we want anyways."

src/lib.rs

@@ -8,6 +8,7 @@ pub mod error;
 mod functions;
 mod internal_rep;
 mod obj_class;
+mod sexp_internal;
 
 use error::{HLLErrorItem, HLLErrors};
 use lalrpop_util::ParseError;
@@ -48,7 +49,7 @@ fn parse_policy<'a>(
 
 fn generate_cil(v: Vec<sexp::Sexp>) -> String {
     v.iter()
-        .map(|s| s.to_string())
+        .map(|s| sexp_internal::display_cil(s))
         .collect::<Vec<String>>()
         .join("\n")
 }

src/sexp_internal.rs

@@ -0,0 +1,48 @@
+use sexp::*;
+
+// the sexp crate doesn't treat foo and "foo" as separate strings, which we need
+// The quoting behavior in the sexp crate automatically handles quoting in situations where the
+// string contains a quote or a space, so we need to avoid those in order for this to work, but 1.
+// We want to avoid those anyways and 2. The default behavior makes actually inserting a quoted
+// string that wouldn't be automatically quoted impossible.
+// https://github.com/cgaebel/sexp/issues/2
+pub fn display_cil(expr: &sexp::Sexp) -> String {
+    match expr {
+        Sexp::List(l) => {
+            format!(
+                "({})",
+                l.iter()
+                    .map(|s| display_cil(s))
+                    .collect::<Vec<String>>()
+                    .join(" ")
+            )
+        }
+        Sexp::Atom(a) => match a {
+            Atom::S(s) => s.to_string(),
+            _ => a.to_string(),
+        },
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_display_cil() {
+        let cil = parse("(foo)").unwrap();
+        assert_eq!(display_cil(&cil), cil.to_string());
+
+        let cil = parse("(foo (bar baz))").unwrap();
+        assert_eq!(display_cil(&cil), cil.to_string());
+
+        let cil = parse("foo").unwrap();
+        assert_eq!(display_cil(&cil), cil.to_string());
+
+        let cil = parse("32").unwrap();
+        assert_eq!(display_cil(&cil), cil.to_string());
+
+        let cil = atom_s("\"/bin\"");
+        assert_eq!(display_cil(&cil), "\"/bin\"".to_string());
+    }
+}