In passthrough security model, following symbolic links in the server side could result in TOCTTOU vulnerabilities. (http://en.wikipedia.org/wiki/Time-of-check-to-time-of-use)
This patchset resolves this issue by creating a dedicated process which chroots into the share path and all file object access are done in the chroot environment. This patchset implements chroot environment, provides necessary functions that can be used by the passthrough function calls. Qemu need to be invoked by root user for using virtfs with passthrough security model (i.e to use chroot() syscall). Question is: Is running qemu by root user expected and allowed? Some of the virtfs features can be utilized only if qemu is started by root user (for example passthrough security model and handle based file driver need root privilege). This issue can be resolved by root user starting qemu and spawning a process with root privilege to do all privileged operations there and main qemu process dropping its privileges to avoid any security issue in running qemu in root mode. Privileged operations can be done similar to the chroot patchset. But how to determine to which user-id(ie non root user id) qemu needs to drop the privileges? Do we have a common user-id across all distributions/systems to which qemu process can be dropped down? Also it becomes too complex i.e when a new feature needing root privilege is added, a process with root privilege needs to be created to handle this. So is it allowed to run qemu by root user? If no, is it okay to add the complexity of adding a root privilege process for each feature that needs root privilege? Changes from version V11: * Rebased on top of latest qemu tree * Moved chroot process creation into local_init function * g_malloc/g_free instead qemu_malloc/g_free * Rename qemu_recv function to chroot_recv Changes from version V10: * Added support to do lstat and readlink from chroot process * Fixed an issue with dealing fds when qemu process reached maxfds limit Changes from version V9: * Error handling in special file object creation in virtio-9p-local.c Changes from version V8: * Make chmod and chown also operate under chroot process * Check for invalid path requests, minor cleanups Changes from version V7: * Add two chroot methods remove and rename * Minor cleanups like consolidating functions Changes from version V6: * Send only fd/errno in socket operations instead of FdInfo structure * Minor cleanups Changes from version V5: * Return errno on failure instead of setting errno * Minor cleanups like updated comments, enable CONFIG_THREAD if CONFIG_VIRTFS is enabled Changes from version V4: * Avoid using malloc/free inside chroot process * Seperate chroot server and client functions Changes from version V3 * Return EIO incase of socket read/write fail instead of exiting * Changed data types as suggested by Blue Swirl * Chroot process reports error through qemu process Changes from version V2 * Treat socket IO errors as fatal, ie qemu will exit * Split patchset based on chroot side (server) and qemu side(client) functionalities M. Mohan Kumar (15): Implement qemu_read_full virtio-9p: Enable CONFIG_THREAD if CONFIG_VIRTFS is enabled virtio-9p: Provide chroot worker side interfaces virtio-9p: qemu interfaces for chroot environment virtio-9p: Support for opening a file in chroot environment virtio-9p: Create support in chroot environment virtio-9p: Creating special files in chroot environment virtio-9p: Removing file or directory in chroot environment virtio-9p: Rename in chroot environment virtio-9p: Move file post creation changes to none security model virtio-9p: chmod in chroot environment virtio-9p: chown in chroot environment virtio-9p: stat in chroot environment virtio-9p: readlink in chroot environment virtio-9p: Chroot environment for other functions Makefile.objs | 1 + configure | 1 + fsdev/file-op-9p.h | 3 + hw/9pfs/virtio-9p-chroot-worker.c | 413 +++++++++++++++++++++++++++++++++++++ hw/9pfs/virtio-9p-chroot.c | 173 ++++++++++++++++ hw/9pfs/virtio-9p-chroot.h | 54 +++++ hw/9pfs/virtio-9p-device.c | 1 + hw/9pfs/virtio-9p-local.c | 277 ++++++++++++++++++++----- osdep.c | 32 +++ qemu-common.h | 2 + 10 files changed, 907 insertions(+), 50 deletions(-) create mode 100644 hw/9pfs/virtio-9p-chroot-worker.c create mode 100644 hw/9pfs/virtio-9p-chroot.c create mode 100644 hw/9pfs/virtio-9p-chroot.h -- 1.7.5.4
