Re: [Qemu-devel] [PATCH 1/1] block_crypto_co_create_generic: clean up created file on failure

[Daniel Henrique Barboza]

On 3/20/19 6:52 AM, Daniel P. Berrangé wrote:
> On Tue, Mar 19, 2019 at 07:03:30PM -0300, Daniel Henrique Barboza wrote:
> > When using a non-UTF8 secret to create a volume using qemu-img, the
> > following error happens:
> >
> > $ qemu-img create -f luks --object 
> > secret,id=vol_1_encrypt0,file=vol_resize_pool.vol_1.secret.qzVQrI -o 
> > key-secret=vol_1_encrypt0 /var/tmp/pool_target/vol_1 10240K
> >
> > Formatting '/var/tmp/pool_target/vol_1', fmt=luks size=10485760 
> > key-secret=vol_1_encrypt0
> > qemu-img: /var/tmp/pool_target/vol_1: Data from secret vol_1_encrypt0 is not 
> > valid UTF-8
> >
> > However, the created file /var/tmp/pool_target/vol_1 is left behind in the
> > file system after the failure. This behavior can be observed when creating
> > the volume using Libvirt, via 'virsh vol-create', and then getting "volume
> > target path already exist" errors when trying to re-create the volume.
> >
> > The volume file is created inside block_crypto_co_create_opts_luks, in
> > block/crypto.c. If the bdrv_create_file() call is successful but any
> > succeeding step fails*, the existing 'fail' label does not take into
> > account the created file, leaving it behind.
> >
> > This patch fixes it by adding a flag to indicate whether bdrv_create_file()
> > created the file, and then unlinking it in the 'fail' label if
> > necessary.
> >
> > * in our case, block_crypto_co_create_generic calls qcrypto_block_create,
> > which calls qcrypto_block_luks_create, and this function fails when
> > calling qcrypto_secret_lookup_as_utf8.
> >
> > Reported-by: Srikanth Aithal <address@hidden>
> > Signed-off-by: Daniel Henrique Barboza <address@hidden>
> > ---
> >   block/crypto.c | 9 +++++++++
> >   1 file changed, 9 insertions(+)
> >
> > diff --git a/block/crypto.c b/block/crypto.c
> > index fd8c7cfac6..5b43424845 100644
> > --- a/block/crypto.c
> > +++ b/block/crypto.c
> > @@ -533,6 +533,7 @@ static int coroutine_fn 
> > block_crypto_co_create_opts_luks(const char *filename,
> >       BlockDriverState *bs = NULL;
> >       QDict *cryptoopts;
> >       int64_t size;
> > +    bool filecreated = false;
> >       int ret;
> >   
> >       /* Parse options */
> > @@ -554,6 +555,7 @@ static int coroutine_fn 
> > block_crypto_co_create_opts_luks(const char *filename,
> >       if (ret < 0) {
> >           goto fail;
> >       }
> > +    filecreated = true;
> >   
> >       bs = bdrv_open(filename, NULL, NULL,
> >                      BDRV_O_RDWR | BDRV_O_RESIZE | BDRV_O_PROTOCOL, errp);
> > @@ -569,7 +571,14 @@ static int coroutine_fn 
> > block_crypto_co_create_opts_luks(const char *filename,
> >       }
> >   
> >       ret = 0;
> > +    goto cleanup;
> > +
> >   fail:
> > +    if (filecreated) {
> > +        unlink(filename);
> You can't do this I'm afraid.
>
> "filename" cannot be assumed to be a local file - it can be an arbitrary
> block device backend string.
>
> Contrary to what you might expect, given the call to bdrv_create_file,
> we can't actually assume this method created the file either. The above
> bdrv_create_file method may have merely formatted a pre-existing volume.
>
> To fix this requires a "bdrv_delete" callback in the BlockDriver code,
> and the actual deletion would need to be done in the "qemu-img create"
> code.


Thanks for the pointers. I'll see if I can make this happen in v2.



DHB


> Regards,
> Daniel