mirror of
https://github.com/xemu-project/xemu.git
synced 2026-07-11 01:24:41 +02:00
Eric Blake
2e909d7ca9
Ever since CVE-2024-4467 (see commit 7ead9469 in qemu v9.1.0), we have
intentionally treated the opening of secondary files whose name is
specified in the contents of the primary file, such as a qcow2
data_file, as something that must be a local file and not a protocol
prefix (it is still possible to open a qcow2 file that wraps an NBD
data image by using QMP commands, but that is from the explicit action
of the QMP overriding any string encoded in the qcow2 file). At the
time, we did not prevent the use of protocol prefixes on the secondary
image while creating a qcow2 file, but it results in a qcow2 file that
records an empty string for the data_file, rather than the protocol
passed in during creation:
$ qemu-img create -f raw datastore.raw 2G
$ qemu-nbd -e 0 -t -f raw datastore.raw &
$ qemu-img create -f qcow2 -o data_file=nbd://localhost:10809/ \
datastore_nbd.qcow2 2G
Formatting 'datastore_nbd.qcow2', fmt=qcow2 cluster_size=65536 extended_l2=off compression_type=zlib size=2147483648 data_file=nbd://localhost:10809/ lazy_refcounts=off refcount_bits=16
$ qemu-img info datastore_nbd.qcow2 | grep data
$ qemu-img info datastore_nbd.qcow2 | grep data
image: datastore_nbd.qcow2
data file:
data file raw: false
filename: datastore_nbd.qcow2
And since an empty string was recorded in the file, attempting to open
the image without using QMP to supply the NBD data store fails, with a
somewhat confusing error message:
$ qemu-io -f qcow2 datastore_nbd.qcow2
qemu-io: can't open device datastore_nbd.qcow2: The 'file' block driver requires a file name
Although the ability to create an image with a convenience reference
to a protocol data file is not a security hole (unlike the case with
open, the image is not untrusted if we are the ones creating it), the
above demo shows that it is still inconsistent. Thus, it makes more
sense if we also insist that image creation rejects a protocol prefix
when using the same syntax. Now, the above attempt produces:
$ qemu-img create -f qcow2 -o data_file=nbd://localhost:10809/ \
datastore_nbd.qcow2 2G
Formatting 'datastore_nbd.qcow2', fmt=qcow2 cluster_size=65536 extended_l2=off compression_type=zlib size=2147483648 data_file=nbd://localhost:10809/ lazy_refcounts=off refcount_bits=16
qemu-img: datastore_nbd.qcow2: Could not create 'nbd://localhost:10809/': No such file or directory
with datastore_nbd.qcow2 no longer created.
Signed-off-by: Eric Blake <eblake@redhat.com>
Message-ID: <20250915213919.3121401-6-eblake@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
=========== QEMU README =========== QEMU is a generic and open source machine & userspace emulator and virtualizer. QEMU is capable of emulating a complete machine in software without any need for hardware virtualization support. By using dynamic translation, it achieves very good performance. QEMU can also integrate with the Xen and KVM hypervisors to provide emulated hardware while allowing the hypervisor to manage the CPU. With hypervisor support, QEMU can achieve near native performance for CPUs. When QEMU emulates CPUs directly it is capable of running operating systems made for one machine (e.g. an ARMv7 board) on a different machine (e.g. an x86_64 PC board). QEMU is also capable of providing userspace API virtualization for Linux and BSD kernel interfaces. This allows binaries compiled against one architecture ABI (e.g. the Linux PPC64 ABI) to be run on a host using a different architecture ABI (e.g. the Linux x86_64 ABI). This does not involve any hardware emulation, simply CPU and syscall emulation. QEMU aims to fit into a variety of use cases. It can be invoked directly by users wishing to have full control over its behaviour and settings. It also aims to facilitate integration into higher level management layers, by providing a stable command line interface and monitor API. It is commonly invoked indirectly via the libvirt library when using open source applications such as oVirt, OpenStack and virt-manager. QEMU as a whole is released under the GNU General Public License, version 2. For full licensing details, consult the LICENSE file. Documentation ============= Documentation can be found hosted online at `<https://www.qemu.org/documentation/>`_. The documentation for the current development version that is available at `<https://www.qemu.org/docs/master/>`_ is generated from the ``docs/`` folder in the source tree, and is built by `Sphinx <https://www.sphinx-doc.org/en/master/>`_. Building ======== QEMU is multi-platform software intended to be buildable on all modern Linux platforms, OS-X, Win32 (via the Mingw64 toolchain) and a variety of other UNIX targets. The simple steps to build QEMU are: .. code-block:: shell mkdir build cd build ../configure make Additional information can also be found online via the QEMU website: * `<https://wiki.qemu.org/Hosts/Linux>`_ * `<https://wiki.qemu.org/Hosts/Mac>`_ * `<https://wiki.qemu.org/Hosts/W32>`_ Submitting patches ================== The QEMU source code is maintained under the GIT version control system. .. code-block:: shell git clone https://gitlab.com/qemu-project/qemu.git When submitting patches, one common approach is to use 'git format-patch' and/or 'git send-email' to format & send the mail to the qemu-devel@nongnu.org mailing list. All patches submitted must contain a 'Signed-off-by' line from the author. Patches should follow the guidelines set out in the `style section <https://www.qemu.org/docs/master/devel/style.html>`_ of the Developers Guide. Additional information on submitting patches can be found online via the QEMU website: * `<https://wiki.qemu.org/Contribute/SubmitAPatch>`_ * `<https://wiki.qemu.org/Contribute/TrivialPatches>`_ The QEMU website is also maintained under source control. .. code-block:: shell git clone https://gitlab.com/qemu-project/qemu-web.git * `<https://www.qemu.org/2017/02/04/the-new-qemu-website-is-up/>`_ A 'git-publish' utility was created to make above process less cumbersome, and is highly recommended for making regular contributions, or even just for sending consecutive patch series revisions. It also requires a working 'git send-email' setup, and by default doesn't automate everything, so you may want to go through the above steps manually for once. For installation instructions, please go to: * `<https://github.com/stefanha/git-publish>`_ The workflow with 'git-publish' is: .. code-block:: shell $ git checkout master -b my-feature $ # work on new commits, add your 'Signed-off-by' lines to each $ git publish Your patch series will be sent and tagged as my-feature-v1 if you need to refer back to it in the future. Sending v2: .. code-block:: shell $ git checkout my-feature # same topic branch $ # making changes to the commits (using 'git rebase', for example) $ git publish Your patch series will be sent with 'v2' tag in the subject and the git tip will be tagged as my-feature-v2. Bug reporting ============= The QEMU project uses GitLab issues to track bugs. Bugs found when running code built from QEMU git or upstream released sources should be reported via: * `<https://gitlab.com/qemu-project/qemu/-/issues>`_ If using QEMU via an operating system vendor pre-built binary package, it is preferable to report bugs to the vendor's own bug tracker first. If the bug is also known to affect latest upstream code, it can also be reported via GitLab. For additional information on bug reporting consult: * `<https://wiki.qemu.org/Contribute/ReportABug>`_ ChangeLog ========= For version history and release notes, please visit `<https://wiki.qemu.org/ChangeLog/>`_ or look at the git history for more detailed information. Contact ======= The QEMU community can be contacted in a number of ways, with the two main methods being email and IRC: * `<mailto:qemu-devel@nongnu.org>`_ * `<https://lists.nongnu.org/mailman/listinfo/qemu-devel>`_ * #qemu on irc.oftc.net Information on additional methods of contacting the community can be found online via the QEMU website: * `<https://wiki.qemu.org/Contribute/StartHere>`_