From 8d048699ee6b33c68f06bc6d0a16e521a733a386 Mon Sep 17 00:00:00 2001
From: bbbradsmith <bbbradsmith@users.noreply.github.com>
Date: Fri, 5 May 2023 21:32:34 -0400
Subject: [PATCH] grc65 fix flawed text parsing Was using fseek(F,-1,SEEK_CUR)
 which is invalid for text files, behaviour unreliable across platforms. Added
 check for internal buffer overflow.

---
 src/grc65/main.c | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/src/grc65/main.c b/src/grc65/main.c
index 349b5c110..ac654300d 100644
--- a/src/grc65/main.c
+++ b/src/grc65/main.c
@@ -850,8 +850,12 @@ static char *filterInput (FILE *F, char *tbl)
     /* loads file into buffer filtering it out */
     int a, prevchar = -1, i = 0, bracket = 0, quote = 1;
 
-    for (;;) {
-        a = getc(F);
+    a = getc(F);
+    while (1)
+    {
+        if (i >= BLOODY_BIG_BUFFER) {
+            AbEnd ("File too large for internal parsing buffer (%d bytes).",BLOODY_BIG_BUFFER);
+        }
         if ((a == '\n') || (a == '\015')) a = ' ';
         if (a == ',' && quote) a = ' ';
         if (a == '\042') quote =! quote;
@@ -873,13 +877,18 @@ static char *filterInput (FILE *F, char *tbl)
             if (a == ';' && quote) {
                 do {
                     a = getc (F);
-                } while (a != '\n');
-                fseek (F, -1, SEEK_CUR);
+                } while (a != '\n' && a != EOF);
+                /* Don't discard this newline/EOF, continue to next loop.
+                ** A previous implementation used fseek(F,-1,SEEK_CUR),
+                ** which is invalid for text mode files, and was unreliable across platforms.
+                */
+                continue;
             } else {
                 tbl[i++] = a;
                 prevchar = a;
             }
         }
+        a = getc(F);
     }
 
     if (bracket != 0) AbEnd ("There are unclosed brackets!");