From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ludovic =?UTF-8?Q?Court=C3=A8s?= <ludo@gnu.org>
Subject: bug#35283: [PATCH] mformat: initialize boot sector before writing it
Date: Sun, 21 Apr 2019 01:03:57 +0200
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	<11201672983044432889@scdbackup.webframe.org>
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Hello,

While investigating reproducible ISO images for Guix=C2=B9, I found that
=E2=80=98mformat=E2=80=99 would not initialize the boot sector before writi=
ng it.  This
led to non-deterministic FAT image contents.

The attached patch fixes that.

Thanks,
Ludo=E2=80=99.

=C2=B9 https://issues.guix.info/issue/35283


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Content-Description: the patch

Fix a bug whereby 'mformat' could end up passing uninitialized bytes
to write(2).  This could be reproduced with:

  mformat -C -f 1440 -L 16  -N 77777777 -i  /tmp/x ::

where the output of /tmp/x would be non-deterministic.

Patch by Ludovic Court=C3=A8s <ludo@gnu.org>.

--- mtools-4.0.23/mformat.c	2019-04-21 00:12:01.496116195 +0200
+++ mtools-4.0.23/mformat.c	2019-04-21 00:12:36.675967157 +0200
@@ -927,6 +927,7 @@ void mformat(int argc, char **argv, int
=20=09
 	char *endptr;
=20
+	memset(&boot.bytes, '\0', sizeof boot);
 	hs =3D hs_set =3D 0;
 	argtracks =3D 0;
 	argheads =3D 0;


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