Re: [Qemu-devel] [PATCH v5 3/4] crypto.c: cleanup created file when block_crypto_co_create_opts_luks fails

[Daniel Henrique Barboza]

On 8/28/19 11:10 PM, John Snow wrote:
> On 8/7/19 10:21 AM, 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 changes block_crypto_co_create_opts_luks() to delete
> > 'filename' in case of failure. A failure in this point means that
> > the volume is now truncated/corrupted, so even if 'filename' was an
> > existing volume before calling qemu-img, it is now unusable. Deleting
> > the file it is not much worse than leaving it in the filesystem in
> > this scenario, and we don't have to deal with checking the file
> > pre-existence in the code.
> >
> > * 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>
> > Suggested-by: Kevin Wolf <address@hidden>
> > Signed-off-by: Daniel Henrique Barboza <address@hidden>
> > ---
> >   block/crypto.c | 20 ++++++++++++++++++++
> >   1 file changed, 20 insertions(+)
> >
> > diff --git a/block/crypto.c b/block/crypto.c
> > index 8237424ae6..8ffca81df6 100644
> > --- a/block/crypto.c
> > +++ b/block/crypto.c
> > @@ -30,6 +30,7 @@
> >   #include "qapi/error.h"
> >   #include "qemu/module.h"
> >   #include "qemu/option.h"
> > +#include "qemu/cutils.h"
> >   #include "crypto.h"
> >   
> >   typedef struct BlockCrypto BlockCrypto;
> > @@ -575,6 +576,25 @@ fail:
> >       bdrv_unref(bs);
> >       qapi_free_QCryptoBlockCreateOptions(create_opts);
> >       qobject_unref(cryptoopts);
> > +
> > +    /*
> > +     * If an error occurred, delete the file. Even if the file existed
> > +     * beforehand, it has been truncated and corrupted in the process.
> > +     */
> > +    if (ret) {
> > +        Error *local_err;
> > +        int r_del = bdrv_delete_file(filename, &local_err);
> > +        /*
> > +         * ENOTSUP will happen if the block driver doesn't support
> > +         * 'bdrv_co_delete_file'. ENOENT will happen if the file
> > +         * doesn't exist. Both are predictable and shouldn't be
> > +         * reported back to the user.
> > +         */
> Hm, actually, didn't you use ENOENT to mean that we couldn't figure out
> which driver to use?


True. In this context though I am referring to the co_routine function
that deletes the file:

-------
(file-posix.c)
static int coroutine_fn raw_co_delete_file(BlockDriverState *bs,
                                           Error **errp)
{
    struct stat st;
    int ret;

    if (!(stat(bs->filename, &st) == 0) || !S_ISREG(st.st_mode)) {
        ret = -ENOENT;
        error_setg_errno(errp, -ret, "%s is not a regular file",
                         bs->filename);
        goto done;
    }
(...)
-----


I'll make it clearer in the comment where ENOENT is coming from.

(In fact, this is a good reason to change the !drv error in patch 2 from
ENOENT to ENOMEDIUM ....)







> > +        if ((r_del < 0) && (r_del != -ENOTSUP) && (r_del != -ENOENT)) {
> > +            error_reportf_err(local_err, "%s: ", bs->filename);
> > +        }> +    }
> > +
> >       return ret;
> >   }
> >