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Hanna Reitz authored
When a curl transfer is finished, that does not mean that CURL lets go
of all the sockets it used for it.  We therefore must not free a
CURLSocket object before CURL has invoked curl_sock_cb() to tell us to
remove it.  Otherwise, we may get a use-after-free, as described in this
bug report: https://bugs.launchpad.net/qemu/+bug/1916501

(Reproducer from that report:
  $ qemu-img convert -f qcow2 -O raw \
  https://download.cirros-cloud.net/0.4.0/cirros-0.4.0-x86_64-disk.img \
  out.img
)

(Alternatively, it might seem logical to force-drop all sockets that
have been used for a state when the respective transfer is done, kind of
like it is done now, but including unsetting the AIO handlers.
Unfortunately, doing so makes the driver just hang instead of crashing,
which seems to evidence that CURL still uses those sockets.)

Make the CURLSocket object independent of "its" CURLState by putting all
sockets into a hash table belonging to the BDRVCURLState instead of a
list that belongs to a CURLState.  Do not touch any sockets in
curl_clean_state().

Testing, it seems like all sockets are indeed gone by the time the curl
BDS is closed, so it seems like there really was no point in freeing any
socket just because a transfer is done.  libcurl does invoke
curl_sock_cb() with CURL_POLL_REMOVE for every socket it has.

Buglink: https://bugs.launchpad.net/qemu/+bug/1916501


Signed-off-by: default avatarMax Reitz <mreitz@redhat.com>
Message-Id: <20210309130541.37540-3-mreitz@redhat.com>
Signed-off-by: default avatarKevin Wolf <kwolf@redhat.com>
0f418a20
History

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:

mkdir build
cd build
../configure
make

Additional information can also be found online via the QEMU website:

Submitting patches

The QEMU source code is maintained under the GIT version control system.

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

The QEMU website is also maintained under source control.

git clone https://gitlab.com/qemu-project/qemu-web.git

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

The workflow with 'git-publish' is:

$ 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:

$ 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 Launchpad as its primary upstream bug tracker. Bugs found when running code built from QEMU git or upstream released sources should be reported via:

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 launchpad.

For additional information on bug reporting consult:

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

Information on additional methods of contacting the community can be found online via the QEMU website: