mirror of https://github.com/xemu-project/xemu.git
6482a96163
When using the passthrough security mode, symbolic links created by the guest are actual symbolic links on the host file system. Since the resolution of symbolic links during path walk is supposed to occur on the client side. The server should hence never receive any path pointing to an actual symbolic link. This isn't guaranteed by the protocol though, and malicious code in the guest can trick the server to issue various syscalls on paths whose one or more elements are symbolic links. In the case of the "local" backend using the "passthrough" or "none" security modes, the guest can directly create symbolic links to arbitrary locations on the host (as per spec). The "mapped-xattr" and "mapped-file" security modes are also affected to a lesser extent as they require some help from an external entity to create actual symbolic links on the host, i.e. another guest using "passthrough" mode for example. The current code hence relies on O_NOFOLLOW and "l*()" variants of system calls. Unfortunately, this only applies to the rightmost path component. A guest could maliciously replace any component in a trusted path with a symbolic link. This could allow any guest to escape a virtfs shared folder. This patch introduces a variant of the openat() syscall that successively opens each path element with O_NOFOLLOW. When passing a file descriptor pointing to a trusted directory, one is guaranteed to be returned a file descriptor pointing to a path which is beneath the trusted directory. This will be used by subsequent patches to implement symlink-safe path walk for any access to the backend. Symbolic links aren't the only threats actually: a malicious guest could change a path element to point to other types of file with undesirable effects: - a named pipe or any other thing that would cause openat() to block - a terminal device which would become QEMU's controlling terminal These issues can be addressed with O_NONBLOCK and O_NOCTTY. Two helpers are introduced: one to open intermediate path elements and one to open the rightmost path element. Suggested-by: Jann Horn <jannh@google.com> Signed-off-by: Greg Kurz <groug@kaod.org> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com> (renamed openat_nofollow() to relative_openat_nofollow(), assert path is relative and doesn't contain '//', fixed side-effect in assert, Greg Kurz) Signed-off-by: Greg Kurz <groug@kaod.org> |
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|---|---|---|
| audio | ||
| backends | ||
| block | ||
| bsd-user | ||
| chardev | ||
| contrib | ||
| crypto | ||
| default-configs | ||
| disas | ||
| docs | ||
| dtc@ec02b34c05 | ||
| fpu | ||
| fsdev | ||
| gdb-xml | ||
| hw | ||
| include | ||
| io | ||
| libdecnumber | ||
| linux-headers | ||
| linux-user | ||
| migration | ||
| nbd | ||
| net | ||
| pc-bios | ||
| pixman@87eea99e44 | ||
| po | ||
| qapi | ||
| qga | ||
| qobject | ||
| qom | ||
| replay | ||
| roms | ||
| scripts | ||
| slirp | ||
| stubs | ||
| target | ||
| tcg | ||
| tests | ||
| trace | ||
| ui | ||
| util | ||
| .dir-locals.el | ||
| .exrc | ||
| .gitignore | ||
| .gitmodules | ||
| .mailmap | ||
| .shippable.yml | ||
| .travis.yml | ||
| CODING_STYLE | ||
| COPYING | ||
| COPYING.LIB | ||
| Changelog | ||
| HACKING | ||
| LICENSE | ||
| MAINTAINERS | ||
| Makefile | ||
| Makefile.objs | ||
| Makefile.target | ||
| README | ||
| VERSION | ||
| accel.c | ||
| arch_init.c | ||
| atomic_template.h | ||
| balloon.c | ||
| block.c | ||
| blockdev-nbd.c | ||
| blockdev.c | ||
| blockjob.c | ||
| bootdevice.c | ||
| bt-host.c | ||
| bt-vhci.c | ||
| configure | ||
| cpu-exec-common.c | ||
| cpu-exec.c | ||
| cpus-common.c | ||
| cpus.c | ||
| cputlb.c | ||
| device-hotplug.c | ||
| device_tree.c | ||
| disas.c | ||
| dma-helpers.c | ||
| dump.c | ||
| exec.c | ||
| gdbstub.c | ||
| hax-stub.c | ||
| hmp-commands-info.hx | ||
| hmp-commands.hx | ||
| hmp.c | ||
| hmp.h | ||
| ioport.c | ||
| iothread.c | ||
| kvm-all.c | ||
| kvm-stub.c | ||
| memory.c | ||
| memory_ldst.inc.c | ||
| memory_mapping.c | ||
| module-common.c | ||
| monitor.c | ||
| numa.c | ||
| os-posix.c | ||
| os-win32.c | ||
| page_cache.c | ||
| qapi-schema.json | ||
| qdev-monitor.c | ||
| qdict-test-data.txt | ||
| qemu-bridge-helper.c | ||
| qemu-doc.texi | ||
| qemu-ga.texi | ||
| qemu-img-cmds.hx | ||
| qemu-img.c | ||
| qemu-img.texi | ||
| qemu-io-cmds.c | ||
| qemu-io.c | ||
| qemu-nbd.c | ||
| qemu-nbd.texi | ||
| qemu-option-trace.texi | ||
| qemu-options-wrapper.h | ||
| qemu-options.h | ||
| qemu-options.hx | ||
| qemu-seccomp.c | ||
| qemu-tech.texi | ||
| qemu.nsi | ||
| qemu.sasl | ||
| qmp.c | ||
| qtest.c | ||
| replication.c | ||
| replication.h | ||
| rules.mak | ||
| softmmu_template.h | ||
| spice-qemu-char.c | ||
| tcg-runtime.c | ||
| tci.c | ||
| thunk.c | ||
| tpm.c | ||
| trace-events | ||
| translate-all.c | ||
| translate-all.h | ||
| translate-common.c | ||
| user-exec-stub.c | ||
| user-exec.c | ||
| version.rc | ||
| vl.c | ||
| xen-common-stub.c | ||
| xen-common.c | ||
| xen-hvm-stub.c | ||
| xen-hvm.c | ||
| xen-mapcache.c | ||
README
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.
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:
http://qemu-project.org/Hosts/Linux
http://qemu-project.org/Hosts/Mac
http://qemu-project.org/Hosts/W32
Submitting patches
==================
The QEMU source code is maintained under the GIT version control system.
git clone git://git.qemu-project.org/qemu.git
When submitting patches, the preferred 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 HACKING and CODING_STYLE files.
Additional information on submitting patches can be found online via
the QEMU website
http://qemu-project.org/Contribute/SubmitAPatch
http://qemu-project.org/Contribute/TrivialPatches
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:
https://bugs.launchpad.net/qemu/
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:
http://qemu-project.org/Contribute/ReportABug
Contact
=======
The QEMU community can be contacted in a number of ways, with the two
main methods being email and IRC
- qemu-devel@nongnu.org
http://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:
http://qemu-project.org/Contribute/StartHere
-- End