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Re: [PATCH v6 07/14] block/crypto: implement the encryption key manageme
From: |
Max Reitz |
Subject: |
Re: [PATCH v6 07/14] block/crypto: implement the encryption key management |
Date: |
Thu, 14 May 2020 16:09:59 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 |
On 10.05.20 15:40, Maxim Levitsky wrote:
> This implements the encryption key management using the generic code in
> qcrypto layer and exposes it to the user via qemu-img
>
> This code adds another 'write_func' because the initialization
> write_func works directly on the underlying file, and amend
> works on instance of luks device.
>
> This commit also adds a 'hack/workaround' I and Kevin Wolf (thanks)
> made to make the driver both support write sharing (to avoid breaking the
> users),
> and be safe against concurrent metadata update (the keyslots)
>
> Eventually the write sharing for luks driver will be deprecated
> and removed together with this hack.
>
> The hack is that we ask (as a format driver) for BLK_PERM_CONSISTENT_READ
> and then when we want to update the keys, we unshare that permission.
> So if someone else has the image open, even readonly, encryption
> key update will fail gracefully.
>
> Also thanks to Daniel Berrange for the idea of
> unsharing read, rather that write permission which allows
> to avoid cases when the other user had opened the image read-only.
>
> Signed-off-by: Maxim Levitsky <address@hidden>
> Reviewed-by: Daniel P. Berrangé <address@hidden>
> ---
> block/crypto.c | 127 +++++++++++++++++++++++++++++++++++++++++++++++--
> block/crypto.h | 34 +++++++++++++
> 2 files changed, 158 insertions(+), 3 deletions(-)
>
> diff --git a/block/crypto.c b/block/crypto.c
> index 2e16b62bdc..b14cb0ff06 100644
> --- a/block/crypto.c
> +++ b/block/crypto.c
[...]
> +static void
> +block_crypto_child_perms(BlockDriverState *bs, BdrvChild *c,
> + const BdrvChildRole *role,
> + BlockReopenQueue *reopen_queue,
> + uint64_t perm, uint64_t shared,
> + uint64_t *nperm, uint64_t *nshared)
> +{
> +
> + BlockCrypto *crypto = bs->opaque;
> +
> + bdrv_filter_default_perms(bs, c, role, reopen_queue,
> + perm, shared, nperm, nshared);
> + /*
> + * Ask for consistent read permission so that if
> + * someone else tries to open this image with this permission
> + * neither will be able to edit encryption keys, since
> + * we will unshare that permission while trying to
> + * update the encryption keys
> + */
> + if (!(bs->open_flags & BDRV_O_NO_IO)) {
> + *nperm |= BLK_PERM_CONSISTENT_READ;
> + }
I’m not sure this is important, because this really means we won’t do
I/O. Its only relevant use in this case is for qemu-img info. Do we
really care if someone edits the key slots while qemu-img info is
processing?
OTOH, I don’t think it’ll harm much. Well, apart from the fact that
BDRV_O_NO_IO won’t do much for LUKS images.
*shrug*
Reviewed-by: Max Reitz <address@hidden>
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- Re: [PATCH v6 05/14] block/amend: refactor qcow2 amend options, (continued)
[PATCH v6 12/14] block/crypto: implement blockdev-amend, Maxim Levitsky, 2020/05/10
[PATCH v6 06/14] block/crypto: rename two functions, Maxim Levitsky, 2020/05/10
[PATCH v6 11/14] block/core: add generic infrastructure for x-blockdev-amend qmp command, Maxim Levitsky, 2020/05/10
[PATCH v6 13/14] block/qcow2: implement blockdev-amend, Maxim Levitsky, 2020/05/10