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Markus Armbruster a1f688f415 block: Deprecate QCOW/QCOW2 encryption 
We've steered users away from QCOW/QCOW2 encryption for a while,
because it's a flawed design (commit 136cd19 Describe flaws in
qcow/qcow2 encryption in the docs).

In addition to flawed crypto, we have comically bad usability, and
plain old bugs.  Let me show you.

= Example images =

I'm going to use a raw image as backing file, and two QCOW2 images,
one encrypted, and one not:

    $ qemu-img create -f raw backing.img 4m
    Formatting 'backing.img', fmt=raw size=4194304
    $ qemu-img create -f qcow2 -o encryption,backing_file=backing.img,backing_fmt=raw geheim.qcow2 4m
    Formatting 'geheim.qcow2', fmt=qcow2 size=4194304 backing_file='backing.img' backing_fmt='raw' encryption=on cluster_size=65536 lazy_refcounts=off
    $ qemu-img create -f qcow2 -o backing_file=backing.img,backing_fmt=raw normal.qcow2 4m
    Formatting 'normal.qcow2', fmt=qcow2 size=4194304 backing_file='backing.img' backing_fmt='raw' encryption=off cluster_size=65536 lazy_refcounts=off

= Usability issues =

== Confusing startup ==

When no image is encrypted, and you don't give -S, QEMU starts the
guest immediately:

    $ qemu-system-x86_64 -nodefaults -display none -monitor stdio normal.qcow2
    QEMU 2.2.50 monitor - type 'help' for more information
    (qemu) info status
    VM status: running

But as soon as there's an encrypted image in play, the guest is *not*
started, with no notification whatsoever:

    $ qemu-system-x86_64 -nodefaults -display none -monitor stdio geheim.qcow2
    QEMU 2.2.50 monitor - type 'help' for more information
    (qemu) info status
    VM status: paused (prelaunch)

If the user figured out that he needs to type "cont" to enter his
keys, the confusion enters the next level: "cont" asks for at most
*one* key.  If more are needed, it then silently does nothing.  The
user has to type "cont" once per encrypted image:

    $ qemu-system-x86_64 -nodefaults -display none -monitor stdio -drive if=none,file=geheim.qcow2 -drive if=none,file=geheim.qcow2
    QEMU 2.2.50 monitor - type 'help' for more information
    (qemu) info status
    VM status: paused (prelaunch)
    (qemu) c
    none0 (geheim.qcow2) is encrypted.
    Password: ******
    (qemu) info status
    VM status: paused (prelaunch)
    (qemu) c
    none1 (geheim.qcow2) is encrypted.
    Password: ******
    (qemu) info status
    VM status: running

== Incorrect passwords not caught ==

All existing encryption schemes give you the GIGO treatment: garbage
password in, garbage data out.  Guests usually refuse to mount
garbage, but other usage is prone to data loss.

== Need to stop the guest to add an encrypted image ==

    $ qemu-system-x86_64 -nodefaults -display none -monitor stdio
    QEMU 2.2.50 monitor - type 'help' for more information
    (qemu) info status
    VM status: running
    (qemu) drive_add "" if=none,file=geheim.qcow2
    Guest must be stopped for opening of encrypted image
    (qemu) stop
    (qemu) drive_add "" if=none,file=geheim.qcow2
    OK

Commit c3adb58 added this restriction.  Before, we could expose images
lacking an encryption key to guests, with potentially catastrophic
results.  See also "Use without key is not always caught".

= Bugs =

== Use without key is not always caught ==

Encrypted images can be in an intermediate state "opened, but no key".
The weird startup behavior and the need to stop the guest are there to
ensure the guest isn't exposed to that state.  But other things still
are!

* drive_backup

    $ qemu-system-x86_64 -nodefaults -display none -monitor stdio geheim.qcow2
    QEMU 2.2.50 monitor - type 'help' for more information
    (qemu) drive_backup -f ide0-hd0 out.img raw
    Formatting 'out.img', fmt=raw size=4194304

  I guess this writes encrypted data to raw image out.img.  Good luck
  with figuring out how to decrypt that again.

* commit

    $ qemu-system-x86_64 -nodefaults -display none -monitor stdio geheim.qcow2
    QEMU 2.2.50 monitor - type 'help' for more information
    (qemu) commit ide0-hd0

  I guess this writes encrypted data into the unencrypted raw backing
  image, effectively destroying it.

== QMP device_add of usb-storage fails when it shouldn't ==

When the image is encrypted, device_add creates the device, defers
actually attaching it to when the key becomes available, then fails.
This is wrong.  device_add must either create the device and succeed,
or do nothing and fail.

    $ qemu-system-x86_64 -nodefaults -display none -usb -qmp stdio -drive if=none,id=foo,file=geheim.qcow2
    {"QMP": {"version": {"qemu": {"micro": 50, "minor": 2, "major": 2}, "package": ""}, "capabilities": []}}
    { "execute": "qmp_capabilities" }
    {"return": {}}
    { "execute": "device_add", "arguments": { "driver": "usb-storage", "id": "bar", "drive": "foo" } }
    {"error": {"class": "DeviceEncrypted", "desc": "'foo' (geheim.qcow2) is encrypted"}}
    {"execute":"device_del","arguments": { "id": "bar" } }
    {"timestamp": {"seconds": 1426003440, "microseconds": 237181}, "event": "DEVICE_DELETED", "data": {"path": "/machine/peripheral/bar/bar.0/legacy[0]"}}
    {"timestamp": {"seconds": 1426003440, "microseconds": 238231}, "event": "DEVICE_DELETED", "data": {"device": "bar", "path": "/machine/peripheral/bar"}}
    {"return": {}}

This stuff is worse than useless, it's a trap for users.

If people become sufficiently interested in encrypted images to
contribute a cryptographically sane implementation for QCOW2 (or
whatever other format), then rewriting the necessary support around it
from scratch will likely be easier and yield better results than
fixing up the existing mess.

Let's deprecate the mess now, drop it after a grace period, and move
on.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
2015-03-16 17:07:25 +01:00

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QA output created by 049
=== Check correct interpretation of suffixes for image size ===
== 1. Traditional size parameter ==
qemu-img create -f qcow2 TEST_DIR/t.qcow2 1024
Formatting 'TEST_DIR/t.qcow2', fmt=qcow2 size=1024 encryption=off cluster_size=65536 lazy_refcounts=off refcount_bits=16
qemu-img create -f qcow2 TEST_DIR/t.qcow2 1024b
Formatting 'TEST_DIR/t.qcow2', fmt=qcow2 size=1024 encryption=off cluster_size=65536 lazy_refcounts=off refcount_bits=16
qemu-img create -f qcow2 TEST_DIR/t.qcow2 1k
Formatting 'TEST_DIR/t.qcow2', fmt=qcow2 size=1024 encryption=off cluster_size=65536 lazy_refcounts=off refcount_bits=16
qemu-img create -f qcow2 TEST_DIR/t.qcow2 1K
Formatting 'TEST_DIR/t.qcow2', fmt=qcow2 size=1024 encryption=off cluster_size=65536 lazy_refcounts=off refcount_bits=16
qemu-img create -f qcow2 TEST_DIR/t.qcow2 1M
Formatting 'TEST_DIR/t.qcow2', fmt=qcow2 size=1048576 encryption=off cluster_size=65536 lazy_refcounts=off refcount_bits=16
qemu-img create -f qcow2 TEST_DIR/t.qcow2 1G
Formatting 'TEST_DIR/t.qcow2', fmt=qcow2 size=1073741824 encryption=off cluster_size=65536 lazy_refcounts=off refcount_bits=16
qemu-img create -f qcow2 TEST_DIR/t.qcow2 1T
Formatting 'TEST_DIR/t.qcow2', fmt=qcow2 size=1099511627776 encryption=off cluster_size=65536 lazy_refcounts=off refcount_bits=16
qemu-img create -f qcow2 TEST_DIR/t.qcow2 1024.0
Formatting 'TEST_DIR/t.qcow2', fmt=qcow2 size=1024 encryption=off cluster_size=65536 lazy_refcounts=off refcount_bits=16
qemu-img create -f qcow2 TEST_DIR/t.qcow2 1024.0b
Formatting 'TEST_DIR/t.qcow2', fmt=qcow2 size=1024 encryption=off cluster_size=65536 lazy_refcounts=off refcount_bits=16
qemu-img create -f qcow2 TEST_DIR/t.qcow2 1.5k
Formatting 'TEST_DIR/t.qcow2', fmt=qcow2 size=1536 encryption=off cluster_size=65536 lazy_refcounts=off refcount_bits=16
qemu-img create -f qcow2 TEST_DIR/t.qcow2 1.5K
Formatting 'TEST_DIR/t.qcow2', fmt=qcow2 size=1536 encryption=off cluster_size=65536 lazy_refcounts=off refcount_bits=16
qemu-img create -f qcow2 TEST_DIR/t.qcow2 1.5M
Formatting 'TEST_DIR/t.qcow2', fmt=qcow2 size=1572864 encryption=off cluster_size=65536 lazy_refcounts=off refcount_bits=16
qemu-img create -f qcow2 TEST_DIR/t.qcow2 1.5G
Formatting 'TEST_DIR/t.qcow2', fmt=qcow2 size=1610612736 encryption=off cluster_size=65536 lazy_refcounts=off refcount_bits=16
qemu-img create -f qcow2 TEST_DIR/t.qcow2 1.5T
Formatting 'TEST_DIR/t.qcow2', fmt=qcow2 size=1649267441664 encryption=off cluster_size=65536 lazy_refcounts=off refcount_bits=16
== 2. Specifying size via -o ==
qemu-img create -f qcow2 -o size=1024 TEST_DIR/t.qcow2
Formatting 'TEST_DIR/t.qcow2', fmt=qcow2 size=1024 encryption=off cluster_size=65536 lazy_refcounts=off refcount_bits=16
qemu-img create -f qcow2 -o size=1024b TEST_DIR/t.qcow2
Formatting 'TEST_DIR/t.qcow2', fmt=qcow2 size=1024 encryption=off cluster_size=65536 lazy_refcounts=off refcount_bits=16
qemu-img create -f qcow2 -o size=1k TEST_DIR/t.qcow2
Formatting 'TEST_DIR/t.qcow2', fmt=qcow2 size=1024 encryption=off cluster_size=65536 lazy_refcounts=off refcount_bits=16
qemu-img create -f qcow2 -o size=1K TEST_DIR/t.qcow2
Formatting 'TEST_DIR/t.qcow2', fmt=qcow2 size=1024 encryption=off cluster_size=65536 lazy_refcounts=off refcount_bits=16
qemu-img create -f qcow2 -o size=1M TEST_DIR/t.qcow2
Formatting 'TEST_DIR/t.qcow2', fmt=qcow2 size=1048576 encryption=off cluster_size=65536 lazy_refcounts=off refcount_bits=16
qemu-img create -f qcow2 -o size=1G TEST_DIR/t.qcow2
Formatting 'TEST_DIR/t.qcow2', fmt=qcow2 size=1073741824 encryption=off cluster_size=65536 lazy_refcounts=off refcount_bits=16
qemu-img create -f qcow2 -o size=1T TEST_DIR/t.qcow2
Formatting 'TEST_DIR/t.qcow2', fmt=qcow2 size=1099511627776 encryption=off cluster_size=65536 lazy_refcounts=off refcount_bits=16
qemu-img create -f qcow2 -o size=1024.0 TEST_DIR/t.qcow2
Formatting 'TEST_DIR/t.qcow2', fmt=qcow2 size=1024 encryption=off cluster_size=65536 lazy_refcounts=off refcount_bits=16
qemu-img create -f qcow2 -o size=1024.0b TEST_DIR/t.qcow2
Formatting 'TEST_DIR/t.qcow2', fmt=qcow2 size=1024 encryption=off cluster_size=65536 lazy_refcounts=off refcount_bits=16
qemu-img create -f qcow2 -o size=1.5k TEST_DIR/t.qcow2
Formatting 'TEST_DIR/t.qcow2', fmt=qcow2 size=1536 encryption=off cluster_size=65536 lazy_refcounts=off refcount_bits=16
qemu-img create -f qcow2 -o size=1.5K TEST_DIR/t.qcow2
Formatting 'TEST_DIR/t.qcow2', fmt=qcow2 size=1536 encryption=off cluster_size=65536 lazy_refcounts=off refcount_bits=16
qemu-img create -f qcow2 -o size=1.5M TEST_DIR/t.qcow2
Formatting 'TEST_DIR/t.qcow2', fmt=qcow2 size=1572864 encryption=off cluster_size=65536 lazy_refcounts=off refcount_bits=16
qemu-img create -f qcow2 -o size=1.5G TEST_DIR/t.qcow2
Formatting 'TEST_DIR/t.qcow2', fmt=qcow2 size=1610612736 encryption=off cluster_size=65536 lazy_refcounts=off refcount_bits=16
qemu-img create -f qcow2 -o size=1.5T TEST_DIR/t.qcow2
Formatting 'TEST_DIR/t.qcow2', fmt=qcow2 size=1649267441664 encryption=off cluster_size=65536 lazy_refcounts=off refcount_bits=16
== 3. Invalid sizes ==
qemu-img create -f qcow2 TEST_DIR/t.qcow2 -- -1024
qemu-img: Image size must be less than 8 EiB!
qemu-img create -f qcow2 -o size=-1024 TEST_DIR/t.qcow2
qemu-img: qcow2 doesn't support shrinking images yet
qemu-img: TEST_DIR/t.qcow2: Could not resize image: Operation not supported
Formatting 'TEST_DIR/t.qcow2', fmt=qcow2 size=-1024 encryption=off cluster_size=65536 lazy_refcounts=off refcount_bits=16
qemu-img create -f qcow2 TEST_DIR/t.qcow2 -- -1k
qemu-img: Image size must be less than 8 EiB!
qemu-img create -f qcow2 -o size=-1k TEST_DIR/t.qcow2
qemu-img: qcow2 doesn't support shrinking images yet
qemu-img: TEST_DIR/t.qcow2: Could not resize image: Operation not supported
Formatting 'TEST_DIR/t.qcow2', fmt=qcow2 size=-1024 encryption=off cluster_size=65536 lazy_refcounts=off refcount_bits=16
qemu-img create -f qcow2 TEST_DIR/t.qcow2 -- 1kilobyte
qemu-img: Invalid image size specified! You may use k, M, G, T, P or E suffixes for
qemu-img: kilobytes, megabytes, gigabytes, terabytes, petabytes and exabytes.
qemu-img create -f qcow2 -o size=1kilobyte TEST_DIR/t.qcow2
Formatting 'TEST_DIR/t.qcow2', fmt=qcow2 size=1024 encryption=off cluster_size=65536 lazy_refcounts=off refcount_bits=16
qemu-img create -f qcow2 TEST_DIR/t.qcow2 -- foobar
qemu-img: Invalid image size specified! You may use k, M, G, T, P or E suffixes for
qemu-img: kilobytes, megabytes, gigabytes, terabytes, petabytes and exabytes.
qemu-img create -f qcow2 -o size=foobar TEST_DIR/t.qcow2
qemu-img: Parameter 'size' expects a size
qemu-img: TEST_DIR/t.qcow2: Invalid options for file format 'qcow2'
== Check correct interpretation of suffixes for cluster size ==
qemu-img create -f qcow2 -o cluster_size=1024 TEST_DIR/t.qcow2 64M
Formatting 'TEST_DIR/t.qcow2', fmt=qcow2 size=67108864 encryption=off cluster_size=1024 lazy_refcounts=off refcount_bits=16
qemu-img create -f qcow2 -o cluster_size=1024b TEST_DIR/t.qcow2 64M
Formatting 'TEST_DIR/t.qcow2', fmt=qcow2 size=67108864 encryption=off cluster_size=1024 lazy_refcounts=off refcount_bits=16
qemu-img create -f qcow2 -o cluster_size=1k TEST_DIR/t.qcow2 64M
Formatting 'TEST_DIR/t.qcow2', fmt=qcow2 size=67108864 encryption=off cluster_size=1024 lazy_refcounts=off refcount_bits=16
qemu-img create -f qcow2 -o cluster_size=1K TEST_DIR/t.qcow2 64M
Formatting 'TEST_DIR/t.qcow2', fmt=qcow2 size=67108864 encryption=off cluster_size=1024 lazy_refcounts=off refcount_bits=16
qemu-img create -f qcow2 -o cluster_size=1M TEST_DIR/t.qcow2 64M
Formatting 'TEST_DIR/t.qcow2', fmt=qcow2 size=67108864 encryption=off cluster_size=1048576 lazy_refcounts=off refcount_bits=16
qemu-img create -f qcow2 -o cluster_size=1024.0 TEST_DIR/t.qcow2 64M
Formatting 'TEST_DIR/t.qcow2', fmt=qcow2 size=67108864 encryption=off cluster_size=1024 lazy_refcounts=off refcount_bits=16
qemu-img create -f qcow2 -o cluster_size=1024.0b TEST_DIR/t.qcow2 64M
Formatting 'TEST_DIR/t.qcow2', fmt=qcow2 size=67108864 encryption=off cluster_size=1024 lazy_refcounts=off refcount_bits=16
qemu-img create -f qcow2 -o cluster_size=0.5k TEST_DIR/t.qcow2 64M
Formatting 'TEST_DIR/t.qcow2', fmt=qcow2 size=67108864 encryption=off cluster_size=512 lazy_refcounts=off refcount_bits=16
qemu-img create -f qcow2 -o cluster_size=0.5K TEST_DIR/t.qcow2 64M
Formatting 'TEST_DIR/t.qcow2', fmt=qcow2 size=67108864 encryption=off cluster_size=512 lazy_refcounts=off refcount_bits=16
qemu-img create -f qcow2 -o cluster_size=0.5M TEST_DIR/t.qcow2 64M
Formatting 'TEST_DIR/t.qcow2', fmt=qcow2 size=67108864 encryption=off cluster_size=524288 lazy_refcounts=off refcount_bits=16
== Check compat level option ==
qemu-img create -f qcow2 -o compat=0.10 TEST_DIR/t.qcow2 64M
Formatting 'TEST_DIR/t.qcow2', fmt=qcow2 size=67108864 compat='0.10' encryption=off cluster_size=65536 lazy_refcounts=off refcount_bits=16
qemu-img create -f qcow2 -o compat=1.1 TEST_DIR/t.qcow2 64M
Formatting 'TEST_DIR/t.qcow2', fmt=qcow2 size=67108864 compat='1.1' encryption=off cluster_size=65536 lazy_refcounts=off refcount_bits=16
qemu-img create -f qcow2 -o compat=0.42 TEST_DIR/t.qcow2 64M
qemu-img: TEST_DIR/t.qcow2: Invalid compatibility level: '0.42'
Formatting 'TEST_DIR/t.qcow2', fmt=qcow2 size=67108864 compat='0.42' encryption=off cluster_size=65536 lazy_refcounts=off refcount_bits=16
qemu-img create -f qcow2 -o compat=foobar TEST_DIR/t.qcow2 64M
qemu-img: TEST_DIR/t.qcow2: Invalid compatibility level: 'foobar'
Formatting 'TEST_DIR/t.qcow2', fmt=qcow2 size=67108864 compat='foobar' encryption=off cluster_size=65536 lazy_refcounts=off refcount_bits=16
== Check preallocation option ==
qemu-img create -f qcow2 -o preallocation=off TEST_DIR/t.qcow2 64M
Formatting 'TEST_DIR/t.qcow2', fmt=qcow2 size=67108864 encryption=off cluster_size=65536 preallocation='off' lazy_refcounts=off refcount_bits=16
qemu-img create -f qcow2 -o preallocation=metadata TEST_DIR/t.qcow2 64M
Formatting 'TEST_DIR/t.qcow2', fmt=qcow2 size=67108864 encryption=off cluster_size=65536 preallocation='metadata' lazy_refcounts=off refcount_bits=16
qemu-img create -f qcow2 -o preallocation=1234 TEST_DIR/t.qcow2 64M
qemu-img: TEST_DIR/t.qcow2: invalid parameter value: 1234
Formatting 'TEST_DIR/t.qcow2', fmt=qcow2 size=67108864 encryption=off cluster_size=65536 preallocation='1234' lazy_refcounts=off refcount_bits=16
== Check encryption option ==
qemu-img create -f qcow2 -o encryption=off TEST_DIR/t.qcow2 64M
Formatting 'TEST_DIR/t.qcow2', fmt=qcow2 size=67108864 encryption=off cluster_size=65536 lazy_refcounts=off refcount_bits=16
qemu-img create -f qcow2 -o encryption=on TEST_DIR/t.qcow2 64M
qemu-img: Encrypted images are deprecated
Support for them will be removed in a future release.
You can use 'qemu-img convert' to convert your image to an unencrypted one.
qemu-img: Encrypted images are deprecated
Support for them will be removed in a future release.
You can use 'qemu-img convert' to convert your image to an unencrypted one.
Formatting 'TEST_DIR/t.qcow2', fmt=qcow2 size=67108864 encryption=on cluster_size=65536 lazy_refcounts=off refcount_bits=16
== Check lazy_refcounts option (only with v3) ==
qemu-img create -f qcow2 -o compat=1.1,lazy_refcounts=off TEST_DIR/t.qcow2 64M
Formatting 'TEST_DIR/t.qcow2', fmt=qcow2 size=67108864 compat='1.1' encryption=off cluster_size=65536 lazy_refcounts=off refcount_bits=16
qemu-img create -f qcow2 -o compat=1.1,lazy_refcounts=on TEST_DIR/t.qcow2 64M
Formatting 'TEST_DIR/t.qcow2', fmt=qcow2 size=67108864 compat='1.1' encryption=off cluster_size=65536 lazy_refcounts=on refcount_bits=16
qemu-img create -f qcow2 -o compat=0.10,lazy_refcounts=off TEST_DIR/t.qcow2 64M
Formatting 'TEST_DIR/t.qcow2', fmt=qcow2 size=67108864 compat='0.10' encryption=off cluster_size=65536 lazy_refcounts=off refcount_bits=16
qemu-img create -f qcow2 -o compat=0.10,lazy_refcounts=on TEST_DIR/t.qcow2 64M
qemu-img: TEST_DIR/t.qcow2: Lazy refcounts only supported with compatibility level 1.1 and above (use compat=1.1 or greater)
Formatting 'TEST_DIR/t.qcow2', fmt=qcow2 size=67108864 compat='0.10' encryption=off cluster_size=65536 lazy_refcounts=on refcount_bits=16
*** done
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