Michael Schmitz - 28.06.18, 07:43:
Joanne,
Linux on m68k has supported lseek64 (or llseek) for a long time (from
glibc version 2.1 according to what I found). About the only area
where we are limited by 32 bits is the virtual memory size.
I'm not proposing to modify the RDB format definition, though an
extension to store 64 bit offsets separate from the 32 bit ones would
be one way to make certain such disks are safe to use on 3.1 and
earlier versions of AmigaOS. (Another one would be to modify the disk
drivers on older versions to do the offset calculation in 64 bit, and
check for overflow just as we do here. Not sure whether that's
feasible. And as you so eloquently describe, we can't rely on users
listening.)
I think that would be up to upstream developers to decide. That would be
AmigaOS developers and/or MorphOS, AROS developers. I could try to at
least point them to this discussion here. Whether they choose to take
the time to look at it? I don´t know. They are developing that stuff in
their spare time.
Either way, we need the cooperation of partitioning tool writers to
ensure partition information that is prone to overflows is never
stored in the 32 bit, classic RDB. That appears to have failed
already, as Martin's experience illustrates.
Heh :)
But yeah, I´d say the damage is done already.
The raw, theoretical limit on the maximum device capacity is about
2^105 bytes:
32 bit rdb_Cylinders * 32 bit rdb_Heads * 32 bit rdb_Sectors * 512
bytes/sector for the HD size in struct RigidDiskBlock
http://wiki.amigaos.net/wiki/RDB
Of course that only holds true for as long as >32 bit math is used :).
So yeah.
I wonder how many Amiga users may try to use such a large disk with a
native operating system that does not support this. NSD64 and TD64 are
at least 10 years old, if not older. Just see the dates in:
http://aminet.net/search?query=nsdpatch
http://aminet.net/package/disk/misc/td64patch
Forget about 10 years. 20 years are more accurate. This stuff is
*ancient*. Officially support is in AmigaOS since version 3.5, which has
been released more than 20 years ago as well:
https://en.wikipedia.org/wiki/AmigaOS_version_history#AmigaOS_3.5,_3.9
Even AmigaOS 4.0 is older than 10 years already.
In any case, it is the responsibility of the tool that creates or change
the RDB to take care of warning the user or using a new format.
Here the kernel just reads that which already exists in the wild.
I'm only concerned with fixing the (dangerous) but in the Linux
partition format parser for RDB. Refusing to use any partitions that
will cause havoc on old AmigaOS versions is all I can do to try and
get the users' attention.
Exactly.
And I do think, that no tool on Linux can create these kind of RDBs, and
if they can… a big fat warning belongs into that tool.
Not even Media Toolbox warns about that currently, so yes… adding an
additional warning in the kernel may be helpful.
However without refusing to parse this, the user may never notice the
warning. So that is an argument for refusing to parse this without a
kernel option.
I still think that is too much hand-holding for the few native OS users
out there. Cause in order to see the warning, the user would have to
stuff the disk into a Linux machine anyway. So the user is still
perfectly able to create such an RDB on AmigaOS 4.x or even AmigaOS
3.5/3.9 or even earlier, and then stuff the disk into a machine with
AmigaOS 1.3 and probably let it go boom there. Now, how many users who
do not know about these limits will ever put the disk into a Linux
machine, receive the warning and then be saved from data destruction? I
bet: None. It is just as unlikely as it can get. :) We are talking about
maybe a few thousand Amiga users here. And there would be even the
question how many of them will try to use disks larger than 2 TiB. I bet
there will be some, but I bet there won´t be many.
So it would be way more important to warn in Media Toolbox, amiga-fdisk,
parted and whatever other partitioning tool users may use.
I´d still leave in the warning anyway, but I think the kernel option… is
over-protecting users.
Anyway your call and I perfectly get it, in case you choose to be on a
100% safe side. You are submitting the patch.
Your warning makes me wonder whether the log message should just say
'report this bug to linux-m68k@xxxxxxxxxxxxxxx' to at least try and
educate any that respond about the dangers of their partitioning
scheme before telling them about the override option. Problem with
that is, in about three years no one will remember any of this ...
Cheers,
Michael
Am 28.06.2018 um 15:44 schrieb jdow:
Michael, as long as m68k only supports int fseek( int ) 4 GB * block
size is your HARD limit. Versions that support __int64 fseek64(
__int64 ) can work with larger disks. RDBs could include RDSK and a
new set of other blocks that replace the last two characters with
"64" and use __int64 where needed in the various values. That way a
clever disk partitioner could give allow normal (32 bit) RDB
definitions where possible. Then at least SOME of the disk could be
supported AND a very clever filesystem that abstracts very large
disks properly could give access to the whole disk. (Read the RDBs
first 32 bits. Then if a filesystem or driveinit was loaded re-read
the RDBs to see if new 64 bit partitions are revealed.
I could be wrong but I do not think RDBs could be safely modified
any
other way to work. And, trust me as I bet this is still true, you
will need a SERIOUSLY good bomb shelter on the Moon if you change
RDBs. Suppose Joe Amigoid uses it, and then Joe Amigoid loads
Amigados 2.4 because he wants to run a game that crashes on
anything newer. Then Joe got far enough something writes to the
disk and data is corrupted. Note further that Amigoids do NOT,
repeat NOT, listen to facts in such cases. Hell, some of them never
listened to facts about an incident at Jerry Pournelle's place when
a 1.1 DPaint session with Kelly Freas hung and we lost a delightful
drawing. Jerry reported it. Amigoids screamed. I tried to tell them
I was there, it was my machine, and 1.1 was, indeed, crap.
{o.o}
On 20180627 02:00, Michael Schmitz wrote:
Joanne,
I'm not at all allergic to avoiding RDB at all cost for new disks.
If
AmigaOS 4.1 supports more recent partition formats, all the better.
This is all about supporting use of legacy RDB disks on Linux
(though
2 TB does stretch the definition of 'legacy' a little). My interest
in this is to ensure we can continue to use RDB format disks on
m68k Amiga computers which have no other way to boot Linux from
disk.
Not proposing to change the RDB format at all, either. Just trying
to
make sure we translate RDB info into Linux 512-byte block offset
and
size numbers correctly. The kernel won't modify the RDB at all
(intentionally, that is - with the correct choice of partition
sizes,
Martin might well have wiped out his RDB with the current version
of
the parser).
The choice of refusing to mount a disk (or mounting read-only)
rests
with the VFS drivers alone - AFFS in that case. Not touching any of
that. At partition scan time, we only have the option of making the
partition available (with a warning printed), or refusing to make
it
available to the kernel. Once it's made available, all bets are
off.
From what Martin writes, his test case RDB was valid and worked as
expected on 32 bit AmigaOS (4.1). Apparently, that version has the
necessary extensions to handle the large offsets resulting from 2
TB
disks. Not sure what safeguards are in place when connecting such a
disk to older versions of AmigaOS, but that is a different matter
entirely.
The overflows in partition offset and size are the only ones I can
see in the partition parser - there is no other overflow I've
identified. I just stated that in order to place a partition
towards the end of a 2 TB disk, the offset calculation will
overflow regardless of what combination of rdb->rdb_BlockBytes and
sector addresses stored in the>>
RDB (in units of 512 byte blocks) we use:
blksize = be32_to_cpu( rdb->rdb_BlockBytes ) / 512;
nr_sects = (be32_to_cpu(pb->pb_Environment[10]) +
1 -
be32_to_cpu(pb->pb_Environment[9])) *
be32_to_cpu(pb->pb_Environment[3]) *
be32_to_cpu(pb->pb_Environment[5]) *
blksize;
if (!nr_sects)
continue;
start_sect = be32_to_cpu(pb->pb_Environment[9]) *
be32_to_cpu(pb->pb_Environment[3]) *
be32_to_cpu(pb->pb_Environment[5]) *
blksize;
But in the interest of avoiding any accidental use of a RDB
partition
where calculations currently overflow, I'll make the default
behaviour to bail out (instead of using wrong offset or size as we
currently do). Given the 'eat_my_RDB_disk=1' boot option, the user
may proceed at their own risk (though I still can't see what harm
should result from now translating a well formed v4.1 2 TB disk
RDB correctly for the first time).
Whether or not Linux correctly handles AFFS filesystems larger than
1
TB is a matter for VFS experts. Bailing out on nr_sects overflowing
ought to prevent accidental use of AFFS filesystems on RDB disks
which I suppose is the majority of use cases.
Bugs in partitioning tools on Linux are entirely out of scope - the
partitioning tools bypass the partition structure discovered by the
kernel, and work straight on the raw device. No protecting against
that.
If you can point out a way to cause data loss with these
precautions,
for a disk 2 TB or larger that was partitioned and used on a recent
version or AmigaOS supporting such large disks, I'd consider
omitting
the 'eat_my_RDB_disk' boot option, and just bail out as the only
safe
option.
Cheers,
Michael
Am 27.06.2018 um 18:24 schrieb jdow:
You allergic to using a GPT solution? It will get away from some
of the evils that RDB has inherent in it because they are also
features? (Loading a filesystem or DriveInit code from RDBs is
just asking for a nearly impossible to remove malware infection.)
Furthermore, any 32 bit system that sees an RDSK block is going
to try to translate it. If you add a new RDB format you are going
to get bizarre and probably quite destructive results from the
mistake. Fail safe is a rather good notion, methinks.
Personally I figure this is all rather surreal. 2TG of junk on an
Amiga system seems utterly outlandish to me. You cited another
overflow potential. There are at least three we've identified, I
believe. Are you 100% sure there are no more? The specific one
you mention of translating RDB to Linux has a proper solution in
the RDB reader. It should recover such overflow errors in the RDB
as it can with due care and polish. It should flag any other
overflow error it detects within the RDBs and return an error
such as to leave the disk unmounted or mounted read-only if you
feel like messing up a poor sod's backups. The simple solution is
to read each of the variables with the nominal RDB size and
convert it to uint64_t before calculating byte indices.
However, consider my inputs as advice from an adult who has seen
the
Amiga Elephant so to speak. I am not trying to assert any control.
Do as you wish; but, I would plead with you to avoid ANY chance
you can for the user to make a bonehead stupid move and lose all
his treasured disk archives. Doing otherwise is very poor form.
{o.o} Joanne "Said enough, she has" Dow
On 20180626 18:07, Michael Schmitz wrote:
Joanne,
As far as I have been able to test, the change is backwards
compatible (RDB partitions from an old disk 80 GB disk are still
recognized OK). That"s only been done on an emulator though.
Your advice about the dangers of using RDB disks that would have
failed the current Linux RDB parser on legacy 32 bit systems is
well
taken though. Maybe Martin can clarify that for me - was the 2 TB
disk in question ever used on a 32 bit Amiga system?
RDB disk format is meant for legacy use only, so I think we can
get
away with printing a big fat warning during boot, advising the
user
that the oversize RDB partition(s) scanned are not compatible
with
legacy 32 bit AmigaOS. With the proposed fix they will work under
both AmigaOS 4.1 and Linux instead of truncating the first
overflowing partition at disk end and trashing valid partitions
that overlap, which is what Martin was after.
If that still seems too risky, we can make the default behaviour
to
bail out once a potential overflow is detected, and allow the
user to
override that through a boot parameter. I'd leave that decision
up for the code review on linux-block.
Two more comments: Linux uses 512 byte block sizes for the
partition
start and size calculations, so a change of the RDB blocksize to
reduce the block counts stored in the RDB would still result in
the
same overflow. And amiga-fdisk is indeed utterly broken and needs
updating (along with probably most legacy m68k partitioners).
Adrian
has advertised parted as replacement for the old tools - maybe
this
would make a nice test case for parted?
Cheers,
Michael
On Tue, Jun 26, 2018 at 9:45 PM, jdow <jdow@xxxxxxxxxxxxx> wrote:
If it is not backwards compatible I for one would refuse to use
it.
And if
it still mattered that much to me I'd also generate a reasonable
alternative. Modifying RDBs nay not be even an approximation of
a
good idea.
You'd discover that as soon as an RDB uint64_t disk is tasted by
a
uint32_t
only system. If it is for your personal use then you're entirely
free to
reject my advice and are probably smart enough to keep it
working for
yourself.
GPT is probably the right way to go. Preserve the ability to
read
RDBs for
legacy disks only.
{^_^}
On 20180626 01:31, Michael Schmitz wrote:
Joanne,
I think we all agree that doing 32 bit calculations on 512-byte
block
addresses that overflow on disks 2 TB and larger is a bug,
causing
the
issues Martin reported. Your patch addresses that by using the
correct
data type for the calculations (as do other partition parsers
that
may
have to deal with large disks) and fixes Martin's bug, so
appears
to be
the right thing to do.
Using 64 bit data types for disks smaller than 2 TB where
calculations
don't currently overflow is not expected to cause new issues,
other
than
enabling use of disk and partitions larger than 2 TB (which may
have
ramifications with filesystems on these partitions). So
comptibility is
preserved.
Forcing larger block sizes might be a good strategy to avoid
overflow
issues in filesystems as well, but I can't see how the block
size
stored
in the RDB would enforce use of the same block size in
filesystems.
We'll have to rely on the filesystem tools to get that right,
too.
Linux
AFFS does allow block sizes up to 4k (VFS limitation) so this
should
allow partitions larger than 2 TB to work already (but I
suspect Al
Viro
may have found a few issues when he looked at the AFFS code so
I
won't
say more). Anyway partitioning tools and filesystems are
unrelated to
the Linux partition parser code which is all we aim to fix in
this
patch.
If you feel strongly about unknown ramifications of any
filesystems on
partitions larger than 2 TB, say so and I'll have the kernel
print a
warning about these partitions.
I'll get this patch tested on Martin's test case image as well
as
on a
RDB image from a disk known to currently work under Linux
(thanks
Geert
for the losetup hint). Can't do much more without procuring a
working
Amiga disk image to use with an emulator, sorry. The Amiga I
plan to
use
for tests is a long way away from my home indeed.
Cheers,
Michael
Am 26.06.18 um 17:17 schrieb jdow:
As long as it preserves compatibility it should be OK, I
suppose.
Personally I'd make any partitioning tool front end gently
force the
block size towards 8k as the disk size gets larger. The file
systems
may also run into 2TB issues that are not obvious. An unused
blocks
list will have to go beyond a uint32_t size, for example. But
a
block
list (OFS for sure, don't remember for the newer AFS) uses a
tad
under
1% of the disk all by itself. A block bitmap is not quite so
bad.
{^_-}
Just be sure you are aware of all the ramifications when you
make a
change. I remember thinking about this for awhile and then
determining
I REALLY did not want to think about it as my brain was
getting tied
into a gordian knot.
{^_^}
On 20180625 19:23, Michael Schmitz wrote:
Joanne,
Martin's boot log (including your patch) says:
Jun 19 21:19:09 merkaba kernel: [ 7891.843284] sdb: RDSK
(512)
sdb1
(LNX^@)(res 2 spb 1) sdb2 (JXF^D)(res 2 spb 1) sdb3
(DOS^C)(res
2 spb
4)
Jun 19 21:19:09 merkaba kernel: [ 7891.844055] sd 7:0:0:0:
[sdb]
Attached SCSI disk
so it's indeed a case of self inflicted damage (RDSK (512)
means
512
byte blocks) and can be worked around by using a different
block
size.
Your memory serves right indeed - blocksize is in 512 bytes
units.
I'll still submit a patch to Jens anyway as this may bite
others
yet.
Cheers,
Michael
On Sun, Jun 24, 2018 at 11:40 PM, jdow <jdow@xxxxxxxxxxxxx>
wrote:
BTW - anybody who uses 512 byte blocks with an Amiga file
system is
a famn
dool.
If memory serves the RDBs think in blocks rather than bytes
so it
should
work up to 2 gigablocks whatever your block size is. 512
blocks is
2199023255552 bytes. But that wastes just a WHOLE LOT of
disk in
block maps.
Go up to 4096 or 8192. The latter is 35 TB.
{^_^}
On 20180624 02:06, Martin Steigerwald wrote:
Hi.
Michael Schmitz - 27.04.18, 04:11:
test results at
https://bugzilla.kernel.org/show_bug.cgi?id=43511
indicate the RDB parser bug is fixed by the patch given
there,
so if
Martin now submits the patch, all should be well?
Ok, better be honest than having anyone waiting for it:
I do not care enough about this, in order to motivate
myself
preparing
the a patch from Joanne Dow´s fix.
I am not even using my Amiga boxes anymore, not even the
Sam440ep
which
I still have in my apartment.
So RDB support in Linux it remains broken for disks larger
2 TB,
unless
someone else does.
Thanks.
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