[src/trunk]: src/usr.bin/xlint/lint1 lint: fix segmentation fault on malforme...

[rillig <rillig%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/796b4dc85a2d
branches:  trunk
changeset: 984334:796b4dc85a2d
user:      rillig <rillig%NetBSD.org@localhost>
date:      Sat Jul 03 20:54:08 2021 +0000

description:
lint: fix segmentation fault on malformed preprocessor output

# 0 ""
# 0 ""2

Found using afl, does not happen in practice though since every C
preprocessor generates balanced 'enter' (1) and 'leave' (2) events.

diffstat:

 usr.bin/xlint/lint1/err.c |  10 ++++++----
 1 files changed, 6 insertions(+), 4 deletions(-)

diffs (31 lines):

diff -r cb66bacbc6be -r 796b4dc85a2d usr.bin/xlint/lint1/err.c
--- a/usr.bin/xlint/lint1/err.c Sat Jul 03 20:43:35 2021 +0000
+++ b/usr.bin/xlint/lint1/err.c Sat Jul 03 20:54:08 2021 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: err.c,v 1.122 2021/06/30 14:23:50 rillig Exp $ */
+/*     $NetBSD: err.c,v 1.123 2021/07/03 20:54:08 rillig Exp $ */
 
 /*
  * Copyright (c) 1994, 1995 Jochen Pohl
@@ -37,7 +37,7 @@
 
 #include <sys/cdefs.h>
 #if defined(__RCSID) && !defined(lint)
-__RCSID("$NetBSD: err.c,v 1.122 2021/06/30 14:23:50 rillig Exp $");
+__RCSID("$NetBSD: err.c,v 1.123 2021/07/03 20:54:08 rillig Exp $");
 #endif
 
 #include <sys/types.h>
@@ -430,8 +430,10 @@
                        free(top);
                        top = includes;
                }
-               top->filename = filename;
-               top->lineno = lineno;
+               if (top != NULL) {
+                       top->filename = filename;
+                       top->lineno = lineno;
+               }
        }
 }