"Daniel P. Berrange" <berrange@redhat.com> writes:
On Tue, Sep 02, 2014 at 03:40:42PM +0800, Chunyan Liu wrote:
To use virtio-serial device, unix socket created for chardev with default umask(022) has insufficient permissions.
e.g. start kvm guest with: -device virtio-serial \ -chardev socket,path=/tmp/foo,server,nowait,id=foo \ -device virtserialport,chardev=foo,name=org.fedoraproject.port.0
Check permissions for the socket file that has been created in the host to enable communication through virtual serial ports in the guest: #ls -l /tmp/somefile.sock srwxr-xr-x 1 qemu qemu 0 21. Jul 14:19 /tmp/somefile.sock
Other users in the qemu group (like real user, test engines, etc) cannot write to this socket.
Problem reported here: https://sourceware.org/bugzilla/show_bug.cgi?id=13078#c11 https://bugzilla.novell.com/show_bug.cgi?id=888166
This patch tries to add a 'umask' option to 'chardev', so that user can have chance to indicate a umask overwritting the default one (default is 022), then create unix sockets with expected permissions.
Signed-off-by: Chunyan Liu <cyliu@suse.com> --- This is patch for qemu.
qemu-char.c | 3 +++ qemu-options.hx | 9 +++++++-- util/qemu-sockets.c | 12 +++++++++++- 3 files changed, 21 insertions(+), 3 deletions(-)
diff --git a/util/qemu-sockets.c b/util/qemu-sockets.c index 5d38395..facf2c6 100644 --- a/util/qemu-sockets.c +++ b/util/qemu-sockets.c @@ -680,7 +680,8 @@ int unix_listen_opts(QemuOpts *opts, Error **errp) { struct sockaddr_un un; const char *path = qemu_opt_get(opts, "path"); - int sock, fd; + int newmask = qemu_opt_get_number(opts, "umask", 0); + int sock, fd, oldmask;
sock = qemu_socket(PF_UNIX, SOCK_STREAM, 0); if (sock < 0) { @@ -708,10 +709,19 @@ int unix_listen_opts(QemuOpts *opts, Error **errp) }
unlink(un.sun_path); + if (newmask) { + oldmask = umask(newmask); + } if (bind(sock, (struct sockaddr*) &un, sizeof(un)) < 0) { + if (newmask) { + umask(oldmask); + } error_set_errno(errp, errno, QERR_SOCKET_BIND_FAILED); goto err; } + if (newmask) { + umask(oldmask); + }
Setting umask() is not thread-safe as it affects the entire process. While this is OK for chardevs which are cold-plugged at startup, once QEMU is running it is not OK to alter umask during hotplug of devices.
Indeed. No telling what else could be affected while the temporary umask is in effect.
Wouldn't it be simpler for libvirt to simply set the umask to 002 when it first launches QEMU, avoiding the need for trying todo this per device.
I guess that's okay as long as you also make sure QEMU's effective group is sane. If you must have laxer permissions just for a specific character device, you can perhaps chmod() after creating it. No good for tightening permissions, of course.