[groff] 23/24: [troff]: Avoid potentially misleading diagnostic.

[G. Branden Robinson]

gbranden pushed a commit to branch master
in repository groff.

commit 5ff8d65c82593b9cc38b84cf36ab121711d64090
Author: G. Branden Robinson <g.branden.robinson@gmail.com>
AuthorDate: Sun Nov 10 12:48:42 2024 -0600

    [troff]: Avoid potentially misleading diagnostic.
    
    * src/roff/troff/input.cpp (diagnose_invalid_identifier): Avoid
      potentially reporting stale token description in diagnostic message,
      using same technique as commit 1277744e72, 20 August.  I was unable to
      verify that the token description really is stale, however.  It might
      not be, since it is lazily computed and the class's `description()`
      member function is not called in the interim, but I also could not
      demonstrate to myself that the relevant diagnostic message is
      reachable.  Use strdup() to copy the token description (grabbing ~30
      bytes from the heap) and free that storage later just in case.
---
 ChangeLog                | 13 +++++++++++++
 src/roff/troff/input.cpp |  6 +++++-
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/ChangeLog b/ChangeLog
index 5ef58af19..c3cefd5be 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,16 @@
+2024-11-10  G. Branden Robinson <g.branden.robinson@gmail.com>
+
+       * src/roff/troff/input.cpp (diagnose_invalid_identifier): Avoid
+       potentially reporting stale token description in diagnostic
+       message, using same technique as commit 1277744e72, 20 August.
+       I was unable to verify that the token description really is
+       stale, however.  It might not be, since it is lazily computed
+       and the class's `description()` member function is not called in
+       the interim, but I also could not demonstrate to myself that the
+       relevant diagnostic message is reachable.  Use strdup() to copy
+       the token description (grabbing ~30 bytes from the heap) and
+       free that storage later just in case.
+
 2024-11-10  G. Branden Robinson <g.branden.robinson@gmail.com>
 
        [troff]: Improve input validation.  Use `has_arg()` (inverted if
diff --git a/src/roff/troff/input.cpp b/src/roff/troff/input.cpp
index cce80ff03..f592f1e78 100644
--- a/src/roff/troff/input.cpp
+++ b/src/roff/troff/input.cpp
@@ -2747,14 +2747,18 @@ static void diagnose_missing_identifier(bool required)
       warning(WARN_MISSING, "missing identifier");
   }
   else if (tok.is_right_brace() || tok.is_tab()) {
-    const char *start = tok.description();
+    // token::description() writes to static, class-wide storage, so we
+    // must allocate a copy of it before issuing the next diagnostic.
+    char *start = strdup(tok.description());
     do {
       tok.next();
     } while (tok.is_space() || tok.is_right_brace() || tok.is_tab());
+    // XXX: unreachable code? --GBR
     if (!tok.is_newline() && !tok.is_eof())
       error("%1 is not allowed before an argument", start);
     else if (required)
       warning(WARN_MISSING, "missing identifier");
+    free(start);
   }
   else if (required)
     error("expected identifier, got %1", tok.description());