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Re: [Qemu-devel] [PATCH 2/3] block/qcow2: fix the corruption when rebasi
From: |
Maxim Levitsky |
Subject: |
Re: [Qemu-devel] [PATCH 2/3] block/qcow2: fix the corruption when rebasing luks encrypted files |
Date: |
Fri, 06 Sep 2019 22:46:06 +0300 |
On Fri, 2019-09-06 at 14:17 -0500, Eric Blake wrote:
> On 9/6/19 12:32 PM, Maxim Levitsky wrote:
> > This fixes subltle corruption introduced by luks threaded encryption
>
> subtle
I usually put the commit messages to a spellchecker, but this time
I forgot to do this. I will try not to in the future.
>
> > in commit 8ac0f15f335
> >
> > Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1745922
> >
> > The corruption happens when we do
> > * write to two or more unallocated clusters at once
> > * write doesn't fully cover nether first nor last cluster
>
> s/nether/neither/
>
> or even:
>
> write doesn't fully cover either the first or the last cluster
I think I didn't wrote the double negative correctly here.
I meant a write that doesn't cover first sector fully and doesn't cover second
sector.
I'll just write it like that I guess.
>
> >
> > In this case, when allocating the new clusters we COW both area
>
> areas
>
> > prior to the write and after the write, and we encrypt them.
> >
> > The above mentioned commit accidently made it so, we encrypt the
>
> accidentally
>
> s/made it so, we encrypt/changed the encryption of/
>
> > second COW are using the physical cluster offset of the first area.
>
> s/are using/to use/
I actually meant to write 'area' here. I just haven't proofed the commit
message at all I confess. Next time I do better.
>
> >
> > Fix this by:
> > * remove the offset_in_cluster parameter of do_perform_cow_encrypt
> > since it is misleading. That offset can be larger that cluster size.
> > instead just add the start and end COW are offsets to both host and
> > guest offsets
> > that do_perform_cow_encrypt receives.
> >
> > * in do_perform_cow_encrypt, remove the cluster offset from the host_offset
> > And thus pass correctly to the qcow2_co_encrypt, the host cluster offset
> > and full guest offset
> >
> >
> > Signed-off-by: Maxim Levitsky <address@hidden>
> > ---
> > block/qcow2-cluster.c | 26 +++++++++++++++-----------
> > 1 file changed, 15 insertions(+), 11 deletions(-)
> >
> > +++ b/block/qcow2-cluster.c
> > @@ -463,20 +463,20 @@ static int coroutine_fn
> > do_perform_cow_read(BlockDriverState *bs,
> > }
> >
> > static bool coroutine_fn do_perform_cow_encrypt(BlockDriverState *bs,
> > - uint64_t
> > guest_cluster_offset,
> > - uint64_t
> > host_cluster_offset,
> > - unsigned offset_in_cluster,
> > + uint64_t guest_offset,
> > + uint64_t host_offset,
> > uint8_t *buffer,
> > unsigned bytes)
> > {
> > if (bytes && bs->encrypted) {
> > BDRVQcow2State *s = bs->opaque;
> > - assert((offset_in_cluster & ~BDRV_SECTOR_MASK) == 0);
> > + assert((guest_offset & ~BDRV_SECTOR_MASK) == 0);
> > + assert((host_offset & ~BDRV_SECTOR_MASK) == 0);
> > assert((bytes & ~BDRV_SECTOR_MASK) == 0);
>
> Pre-existing, but we could use QEMU_IS_ALIGNED(x, BDRV_SECTOR_SIZE) for
> slightly more legibility than open-coding the bit operation.
>
> Neat trick about power-of-2 alignment checks:
>
> assert(QEMU_IS_ALIGNED(offset_in_cluster | guest_offset |
> host_offset | bytes, BDRV_SECTOR_SIZE));
In my book, a shorter code is almost always better, so why not.
>
> gives the same result in one assertion. (I've used it elsewhere in the
> code base, but I'm not opposed to one assert per variable if you think
> batching is too dense.)
>
> I'll let Dan review the actual code change, but offhand it makes sense
> to me.
>
Best regards,
Thanks for the review,
Maxim Levitsky
[Qemu-devel] [PATCH 2/3] block/qcow2: fix the corruption when rebasing luks encrypted files, Maxim Levitsky, 2019/09/06
[Qemu-devel] [PATCH 3/3] qemu-iotests: test for bz #1745922, Maxim Levitsky, 2019/09/06
Re: [Qemu-devel] [PATCH 0/3] Fix qcow2+luks corruption introduced by commit 8ac0f15f335, Maxim Levitsky, 2019/09/06