2.5.5-pre1: mounting NTFS partitions -t VFAT

2.5.5-pre1: mounting NTFS partitions -t VFAT

[Jos Hulzink]

Hi,

Due to a recent change of filesystems, I found the following: 2.5.5-pre1
mounts my NTFS (win2k) partition as VFAT partition, if told to do so. The
kernel returns errors, but the mount is there. One write to the partition
was enough to destroy the entire NTFS partition.

Due to filesystem damage, I didn't test the behaviour of the VFAT driver
on other filesystems yet.

Kernel 2.4.17 also returns errors, but there the mount fails.

Will try to debug the problem myself this afternoon. Sounds like the VFAT
procedure ignores some errors.

Jos

Re: 2.5.5-pre1: mounting NTFS partitions -t VFAT

[Anton Altaparmakov]

On Fri, 15 Feb 2002, Jos Hulzink wrote:
> Due to a recent change of filesystems, I found the following: 2.5.5-pre1
> mounts my NTFS (win2k) partition as VFAT partition, if told to do so. The
> kernel returns errors, but the mount is there. One write to the partition
> was enough to destroy the entire NTFS partition.
>
> Due to filesystem damage, I didn't test the behaviour of the VFAT driver
> on other filesystems yet.
>
> Kernel 2.4.17 also returns errors, but there the mount fails.
>
> Will try to debug the problem myself this afternoon. Sounds like the VFAT
> procedure ignores some errors.

At a guess (V)FAT is not checking the OEM identifier in the bootsector
which for NTFS is defined as "NTFS " (i.e. NTFS followed by four ASCII
spaces, 0x20 char code. The OEMid is at offset 3 (bytes) into the
bootsector.

If you just add a check to (v)fat boot sector sanity verification (it
does have one right? if not it REALLY ought to have one...) and make sure
the OEMid is not the ntfs one the fat driver will never touch the ntfs
partition. Even better if it would check for the correct FAT oem id but I
think there may be several different ones so it may be easier to just make
sure it is not NTFS.

Best regards,

Anton

Re: 2.5.5-pre1: mounting NTFS partitions -t VFAT

[OGAWA Hirofumi]

Jos Hulzink <josh@stack.nl> writes:

> Hi,
> 
> Due to a recent change of filesystems, I found the following: 2.5.5-pre1
> mounts my NTFS (win2k) partition as VFAT partition, if told to do so. The
> kernel returns errors, but the mount is there. One write to the partition
> was enough to destroy the entire NTFS partition.
> 
> Due to filesystem damage, I didn't test the behaviour of the VFAT driver
> on other filesystems yet.
> 
> Kernel 2.4.17 also returns errors, but there the mount fails.
> 
> Will try to debug the problem myself this afternoon. Sounds like the VFAT
> procedure ignores some errors.

Sorry, my fault.

The following patch should fix this bug. I'll submit it after test.

--- fat_bug-2.5.5-pre1/fs/fat/inode.c.orig	Thu Feb 14 13:47:54 2002
+++ fat_bug-2.5.5-pre1/fs/fat/inode.c	Sat Feb 16 05:06:58 2002
@@ -624,6 +624,18 @@
 	}
 
 	b = (struct fat_boot_sector *) bh->b_data;
+	if (!b->fats) {
+		if (!silent)
+			printk("FAT: bogus number of FAT structure\n");
+		brelse(bh);
+		goto out_invalid;
+	}
+	if (!b->reserved) {
+		if (!silent)
+			printk("FAT: bogus number of reserved sectors\n");
+		brelse(bh);
+		goto out_invalid;
+	}
 	if (!b->secs_track) {
 		if (!silent)
 			printk("FAT: bogus sectors-per-track value\n");
-- 
OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>

Re: 2.5.5-pre1: mounting NTFS partitions -t VFAT

[Jos Hulzink]

Hi Ogawa,

Your patch seems to fix it more or less, not the way it should be
fixed, imho.  Partitions other than FAT return bogus information, but
bogus is not always zero. Fortunately enough, one of those new if
statements returns an error, but this is a "works for me"
solution, not a decent one.

What lacks is a fingerprint detector, and iirc -long time ago- FAT has a
very easy to detect fingerprint.

I'll dig into FAT documentation tonight.

Jos

On Sat, 16 Feb 2002, OGAWA Hirofumi wrote:

> Sorry, my fault.
>
> The following patch should fix this bug. I'll submit it after test.
>
> --- fat_bug-2.5.5-pre1/fs/fat/inode.c.orig	Thu Feb 14 13:47:54 2002
> +++ fat_bug-2.5.5-pre1/fs/fat/inode.c	Sat Feb 16 05:06:58 2002
> @@ -624,6 +624,18 @@
>  	}
>
>  	b = (struct fat_boot_sector *) bh->b_data;
> +	if (!b->fats) {
> +		if (!silent)
> +			printk("FAT: bogus number of FAT structure\n");
> +		brelse(bh);
> +		goto out_invalid;
> +	}
> +	if (!b->reserved) {
> +		if (!silent)
> +			printk("FAT: bogus number of reserved sectors\n");
> +		brelse(bh);
> +		goto out_invalid;
> +	}
>  	if (!b->secs_track) {
>  		if (!silent)
>  			printk("FAT: bogus sectors-per-track value\n");
> --
> OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
> -
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at  http://www.tux.org/lkml/
>

Re: 2.5.5-pre1: mounting NTFS partitions -t VFAT

[OGAWA Hirofumi]

Jos Hulzink <josh@stack.nl> writes:

> Hi Ogawa,
> 
> Your patch seems to fix it more or less, not the way it should be
> fixed, imho.  Partitions other than FAT return bogus information, but
> bogus is not always zero. Fortunately enough, one of those new if
> statements returns an error, but this is a "works for me"
> solution, not a decent one.

No, that patch are validity check for FAT, not for you.

> What lacks is a fingerprint detector, and iirc -long time ago- FAT has a
> very easy to detect fingerprint.
> 
> I'll dig into FAT documentation tonight.

I read the document repeatedly and did much tests. If you read the
document, you may use BS_OEMName or BS_FilSysType, however, these
don't have a meaning.
-- 
OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>

VFS issues (was: Re: 2.5.5-pre1: mounting NTFS partitions -t VFAT)

[Jos Hulzink]

On Mon, 18 Feb 2002, OGAWA Hirofumi wrote:

> Jos Hulzink <josh@stack.nl> writes:
>
> > What lacks is a fingerprint detector, and iirc -long time ago- FAT has a
> > very easy to detect fingerprint.
> >
> > I'll dig into FAT documentation tonight.
>
> I read the document repeatedly and did much tests. If you read the
> document, you may use BS_OEMName or BS_FilSysType, however, these
> don't have a meaning.

Hmmm. You seem to be right there. In my OS (IBM PC only) I checked the
partition table (see below).

The first question I want answered: Should I just call myself stupid for
trying to mount NTFS as VFAT, or should we consider this a real issue that
needs fixing ? (I see the problem as a generic problem. There must be
other combinations of filesystems and partition types that pass the
test, but are wrong). IMHO the latter, for every lost partition makes an
angry linux user.

Anyway. I have already been thinking further. Maybe I'm talking nonsense,
but I'll give it a try.

The type of a partition is written in the partition table, or something
similar. Maybe we should check that ?

While mounting a partition, the vfs layer tries to determine the partition
type, and passes that info to the filesystem driver, which checks whether
that partition type can be mounted by the driver. If no partition type is
provided by the vfs layer (for the partition type is not available in the
used partition table, or whatever), the fs driver must try to find out
itself.

If you don't want the calls to change, another option is to move the check
to the vfs. Problem there however is that the vfs needs a "filesystem <->
partition type" table. On the other hand, this way we can add extra
security without breaking anything.

Jos

Re: VFS issues (was: Re: 2.5.5-pre1: mounting NTFS partitions -t VFAT)

[Richard Russon]

Hi Jos,

> The first question I want answered: Should I just call myself stupid for
> trying to mount NTFS as VFAT, or should we consider this a real issue that
> needs fixing ?

Stupid?  No.
Fixing?  Yes.

Whatever you throw at mount, you want it to fail_safe_.  i.e. in the
worst case, do nothing.

> While mounting a partition, the vfs layer tries to determine the partition
> type,

Without any help, mount (userspace) tries to determine the partition
type.  It understands the magics of a LOT of filesystems.

It looks for the NTFS magic before the DOS magic (or any of its variants).

> and passes that info to the filesystem driver

Which is passed to the VFS, and the to the driver which performs some
more rigid tests (hopefully :-)

Cheers,
  FlatCap (Rich)
  ntfs@flatcap.org

Re: VFS issues (was: Re: 2.5.5-pre1: mounting NTFS partitions -t VFAT)

[Jos Hulzink]

On Tuesday 19 February 2002 12:52, Richard Russon wrote:

> Whatever you throw at mount, you want it to fail_safe_.  i.e. in the
> worst case, do nothing.

Agreed.

> Without any help, mount (userspace) tries to determine the partition
> type.  It understands the magics of a LOT of filesystems.
>
> It looks for the NTFS magic before the DOS magic (or any of its variants).

Well, the story: I reinstalled Win2k and updated from FAT32 to NTFS, the day 
before I tested 2.5.5pre-1. I forgot to update /etc/fstab. So mount was 
called with the -t vfat option.

> Which is passed to the VFS, and the to the driver which performs some
> more rigid tests (hopefully :-)

Working on those tests, though it is hard to tell what limits are valid. I 
never saw more than 2 FATs, but can I assume there never will be more ? FAT 
has no real fingerprint, unfortunately. There are some bytes that can be 
checked, but they depend very much on the FAT version. FAT v 4.0 and higher 
have the fingerprint 'FAT' somewhere in the bootsector, but this doesn't hold 
anymore for some Win98/ME formatted partitions.

A test I'm thinking about is trying to match the FATs if there is more than 
one. You want to bail out if the FATs aren't the same anyway. The chance that 
the FAT-sectors are the same on non-FAT partitions is very small. Though this 
test can be rather slow, maybe we should only test the first sector(s).

Jos

Re: VFS issues (was: Re: 2.5.5-pre1: mounting NTFS partitions -t VFAT)

[Alexander Viro]

On Tue, 19 Feb 2002, Jos Hulzink wrote:

> While mounting a partition, the vfs layer tries to determine the partition

It doesn't and it shouldn't.  mount(8) does, so there's no reason to do that
in kerenl.

Re: VFS issues (was: Re: 2.5.5-pre1: mounting NTFS partitions -t VFAT)

[Denis Vlasenko]

> > > What lacks is a fingerprint detector, and iirc -long time ago- FAT has
> > > a very easy to detect fingerprint.
> > >
> > > I'll dig into FAT documentation tonight.
> >
> > I read the document repeatedly and did much tests. If you read the
> > document, you may use BS_OEMName or BS_FilSysType, however, these
> > don't have a meaning.
>
> Hmmm. You seem to be right there. In my OS (IBM PC only) I checked the
> partition table (see below).
>
> The first question I want answered: Should I just call myself stupid for
> trying to mount NTFS as VFAT, or should we consider this a real issue that
> needs fixing ? (I see the problem as a generic problem. There must be
> other combinations of filesystems and partition types that pass the
> test, but are wrong). IMHO the latter, for every lost partition makes an
> angry linux user.
>
> Anyway. I have already been thinking further. Maybe I'm talking nonsense,
> but I'll give it a try.
>
> The type of a partition is written in the partition table, or something
> similar. Maybe we should check that ?

Partition type isn't available to fs driver. Think about mounting 
floppy/loopback/etc.

Seems you guys are discussing non-problem here. What really needs to be done 
is to add more sanity checks to FAT superblock detection/validation code:
* signatures like 55AA at end of 1st sector
* sane values for various superblock data (if you see "FAT copies: 146"
  it is more than enough to tell it's not a FAT, right?)

If anyone feels so inclined, please go to fs/fat/inode.c:fat_read_super()
and hack on it. Send your patches to Alexander Viro <viro@math.psu.edu>
and tighten your seatbelt ;-)

> While mounting a partition, the vfs layer tries to determine the partition
> type, and passes that info to the filesystem driver, which checks whether
> that partition type can be mounted by the driver. If no partition type is
> provided by the vfs layer (for the partition type is not available in the
> used partition table, or whatever), the fs driver must try to find out
> itself.
--
vda

Re: VFS issues (was: Re: 2.5.5-pre1: mounting NTFS partitions -t VFAT)

[Jos Hulzink]

On Tue, 19 Feb 2002, Denis Vlasenko wrote:

> > The type of a partition is written in the partition table, or something
> > similar. Maybe we should check that ?
>
> Partition type isn't available to fs driver. Think about mounting
> floppy/loopback/etc.

True. I never use floppys anymore :)

> Seems you guys are discussing non-problem here. What really needs to be done
> is to add more sanity checks to FAT superblock detection/validation code:
> * signatures like 55AA at end of 1st sector
> * sane values for various superblock data (if you see "FAT copies: 146"
>   it is more than enough to tell it's not a FAT, right?)
>
> If anyone feels so inclined, please go to fs/fat/inode.c:fat_read_super()
> and hack on it. Send your patches to Alexander Viro <viro@math.psu.edu>
> and tighten your seatbelt ;-)

Will hack tonight and see if my seatbelt is strong enough :) It has never
been used before, so maybe...

Jos

[BUG] 2.5.6: IPv6 fails to initialize

[Jos Hulzink]

Hi,

2.5.6 comes with the next error:

Failed to initialize the ICMP6 control socket (err -97).

I have not found any kernel settings that affect this error, it happens
both with IPv6 compiled in kernel and loaded as module.

Jos

Re: [BUG] 2.5.6: IPv6 fails to initialize

[Ben Clifford]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

On Sat, 9 Mar 2002, Jos Hulzink wrote:

> 2.5.6 comes with the next error:
>
> Failed to initialize the ICMP6 control socket (err -97).
>
> I have not found any kernel settings that affect this error, it happens
> both with IPv6 compiled in kernel and loaded as module.

There was a similar problem with the -dj tree a while ago - I think the
solution is probably the same.

Search the archives for the thread titled:

Subject: Linux 2.5.5-dj1 - IPv6 not loading correctly.


- -- 
Ben Clifford     benc@hawaga.org.uk     GPG: 30F06950
http://www.hawaga.org.uk/ben/

-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.0.6 (GNU/Linux)
Comment: For info see http://www.gnupg.org

iD8DBQE8ina8sYXoezDwaVARAl5lAJ4wj6izPK+UhM12uz2axTxLbbVcrACfTEpQ
WdCoZrOWKvWDHWqNI06w+sE=
=dmRK
-----END PGP SIGNATURE-----

Re: [BUG] 2.5.6: IPv6 fails to initialize

[David S. Miller]

This will be fixed shortly.

Re: VFS issues (was: Re: 2.5.5-pre1: mounting NTFS partitions -t VFAT)

[Andries.Brouwer]

    From: Jos Hulzink <josh@stack.nl>

    On Mon, 18 Feb 2002, OGAWA Hirofumi wrote:

    > Jos Hulzink <josh@stack.nl> writes:
    >
    > > What lacks is a fingerprint detector, and iirc -long time ago- FAT has a
    > > very easy to detect fingerprint.
    > >
    > > I'll dig into FAT documentation tonight.
    >
    > I read the document repeatedly and did much tests. If you read the
    > document, you may use BS_OEMName or BS_FilSysType, however, these
    > don't have a meaning.

    Hmmm. You seem to be right there. In my OS (IBM PC only) I checked the
    partition table (see below).

    The first question I want answered: Should I just call myself stupid for
    trying to mount NTFS as VFAT, or should we consider this a real issue that
    needs fixing ? (I see the problem as a generic problem. There must be
    other combinations of filesystems and partition types that pass the
    test, but are wrong). IMHO the latter, for every lost partition makes an
    angry linux user.

    Anyway. I have already been thinking further. Maybe I'm talking nonsense,
    but I'll give it a try.

    The type of a partition is written in the partition table, or something
    similar. Maybe we should check that ?

No.

Letting mount guess is a dangerous business. There is no guarantee
it will guess right, and if mount guesses wrong and the filesystem
was mounted rw, then it may well be trashed.

Doing this right is impossible, and doing this better than today
is of questionable usefulness.

[When guessing reaches a 99.99% probability of success then before
you know it distributions will use guessing in their installation
scripts, and destroy the filesystem of only 1 in 10000 customers.
That single customer always turns out to be me.
When the probability is only 99% people are kept honest.]

FAT is one of the filesystems without really good magic.
But also with filesystems that have good magic one may make
mistakes: several filesystem types have magic in different
blocks, at different offsets. Thus, a partition can have the
magic of more than one filesystem type. This is especially likely
if it had a filesystem of one type before it was reformatted as
another type.
[Zeroing out the first few blocks upon a reformat helps a bit,
but will in some cases destroy a boot loader.]

Now about partition types. First look at
http://www.win.tue.nl/~aeb/partitions/partition_types-1.html
and then consider:
Several dozen types all imply FAT.
The Linux type 83 only says Linux but does not carry information
about the filesystem type. The NTFS type 7 is also the OS/2 type
for HPFS and other installable file systems, and is used by a
few other systems as well.
You see that this is a mess, and in reality no useful information
is to be found here, at most some vague heuristics.

Then consider that partitions can come from BSD slices or other
flavours of partition table or disk label, and that they can be
added by ioctl, so that no partition table need to be present
at all.

So, no, looking at partition types is a very bad idea.

Andries