On 13.09.19 00:30, Maxim Levitsky wrote: > This implements the encryption key management > using the generic code in qcrypto layer > (currently only for qemu-img amend) > > This code adds another 'write_func' because the initialization > write_func works directly on the underlying file, > because during the creation, there is no open instance > of the luks driver, but during regular use, we have it, > and should use it instead. > > > This commit also adds a 'hack/workaround' I and Kevin Wolf (thanks) > made to make the driver still support write sharing, > but be safe against concurrent metadata update (the keys) > Eventually 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 always > (technically always unless opened with BDRV_O_NO_IO) > > and then when we want to update the keys, we > unshare that permission. So if someone else > has the image open, even readonly, this will fail. > > Also thanks to Daniel Berrange for the variant of > that hack that involves asking for read, > rather that write permission > > Signed-off-by: Maxim Levitsky <[email protected]> > --- > block/crypto.c | 118 +++++++++++++++++++++++++++++++++++++++++++++++-- > 1 file changed, 115 insertions(+), 3 deletions(-) > > diff --git a/block/crypto.c b/block/crypto.c > index a6a3e1f1d8..f42fa057e6 100644 > --- a/block/crypto.c > +++ b/block/crypto.c > @@ -36,6 +36,7 @@ typedef struct BlockCrypto BlockCrypto; > > struct BlockCrypto { > QCryptoBlock *block; > + bool updating_keys; > }; > > > @@ -70,6 +71,24 @@ static ssize_t block_crypto_read_func(QCryptoBlock *block, > return ret; > } > > +static ssize_t block_crypto_write_func(QCryptoBlock *block, > + size_t offset, > + const uint8_t *buf, > + size_t buflen, > + void *opaque, > + Error **errp)
There’s already a function of this name for creation.
> +{
> + BlockDriverState *bs = opaque;
> + ssize_t ret;
> +
> + ret = bdrv_pwrite(bs->file, offset, buf, buflen);
> + if (ret < 0) {
> + error_setg_errno(errp, -ret, "Could not write encryption header");
> + return ret;
> + }
> + return ret;
> +}
> +
>
> struct BlockCryptoCreateData {
> BlockBackend *blk;
[...]
> +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;
> +
> + /*
> + * 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
> + */
> + if (!(bs->open_flags & BDRV_O_NO_IO)) {
> + perm |= BLK_PERM_CONSISTENT_READ;
> + }
> +
> + /*
> + * This driver doesn't modify LUKS metadata except
> + * when updating the encryption slots.
> + * Thus unlike a proper format driver we don't ask for
> + * shared write permission. However we need it
> + * when we area updating keys, to ensure that only we
> + * had opened the device r/w
> + *
> + * Encryption update will set the crypto->updating_keys
> + * during that period and refresh permissions
> + *
> + */
> +
> + if (crypto->updating_keys) {
> + /*need exclusive write access for header update */
> + perm |= BLK_PERM_WRITE;
> + shared &= ~(BLK_PERM_CONSISTENT_READ | BLK_PERM_WRITE);
> + }
> +
> + bdrv_filter_default_perms(bs, c, role, reopen_queue,
> + perm, shared, nperm, nshared);
> +}
This will probably work, but usually drivers do it the other way around:
First call any of the default_perms(), and then adjust *nperm and
*nshared as required.
(perm/shared are what the parents need, *nperm/*nshared is what this
driver needs, so it makes more sense that way; and this way nobody has
to check whether the settings survived the default_perms() call.)
((But the permissions themselves do look correct.))
Max
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