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[PATCH] lib/autoconf/c.m4: fix NULL pointer dereference in _AC_LANG_IO_P

From: Nicolas Iooss
Subject: [PATCH] lib/autoconf/c.m4: fix NULL pointer dereference in _AC_LANG_IO_PROGRAM
Date: Mon, 28 Jun 2021 14:13:25 +0200

The following program crashes (with a segmentation fault) when fopen

    #include <stdio.h>
    int main () {
        FILE *f = fopen ("conftest.out", "w");
        return ferror (f) || fclose (f) != 0;

This is due to ferror dereferencing a NULL pointer (using GNU C Library

* lib/autoconf/c.m4: return an error when f is NULL.
 lib/autoconf/c.m4 | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/autoconf/c.m4 b/lib/autoconf/c.m4
index 9f881f0bc10c..0d9efa62d450 100644
--- a/lib/autoconf/c.m4
+++ b/lib/autoconf/c.m4
@@ -114,7 +114,7 @@ $2
 [AC_LANG_PROGRAM([@%:@include <stdio.h>],
 [FILE *f = fopen ("conftest.out", "w");
- return ferror (f) || fclose (f) != 0;
+ return !f || ferror (f) || fclose (f) != 0;


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