When there isn't a ssh -X type session running and a user has not
been added to the libvirt group, attempts to run 'virsh -c qemu:///system'
commands from an otherwise unprivileged user will fail with rather
generic or opaque error message:
"error: authentication failed: no agent is available to authenticate"
This patch will adjust the error code and message to help reflect the
situation that the problem is the requested mechanism is UNAVAILABLE and
a slightly more descriptive error. The result on a failure then becomes:
"error: authentication unavailable: no polkit agent available to
authenticate action 'org.libvirt.unix.manage'"
A bit more history on this - at one time a failure generated the
following type message when running the 'pkcheck' as a subprocess:
"error: authentication failed: polkit\56retains_authorization_after_challenge=1
Authorization requires authentication but no agent is available."
but, a patch was generated to adjust the error message to help provide
more details about what failed. This was pushed as commit id '96a108c99'.
That patch prepended a "polkit: " to the output. It really didn't solve
the problem, but gave a hint.
After some time it was deemed using DBus API calls directly was a
better way to go (since pkcheck calls them anyway). So, commit id
'1b854c76' (more or less) copied the code from remoteDispatchAuthPolkit
and adjusted it. Then commit id 'c7542573' adjusted the remote.c
code to call the new API (virPolkitCheckAuth). Finally, commit id
'308c0c5a' altered the code to call DBus APIs directly. In doing
so, it reverted the failing error message to the generic message
that would have been received from DBus anyway.
Apparently we are not the only ones with dumb free functions
because dbus_message_unref() does not accept NULL either. But if
I were to vote, this one is even more evil. Instead of returning
an error just like we do it immediately dereference any pointer
passed and thus crash you app. Well done DBus!
Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0x7f878ebda700 (LWP 31264)]
0x00007f87be4016e5 in ?? () from /usr/lib64/libdbus-1.so.3
(gdb) bt
#0 0x00007f87be4016e5 in ?? () from /usr/lib64/libdbus-1.so.3
#1 0x00007f87be3f004e in dbus_message_unref () from /usr/lib64/libdbus-1.so.3
#2 0x00007f87bf6ecf95 in virSystemdGetMachineNameByPID (pid=9849) at util/virsystemd.c:228
#3 0x00007f879761bd4d in qemuConnectCgroup (driver=0x7f87600a32a0, vm=0x7f87600c7550) at qemu/qemu_cgroup.c:909
#4 0x00007f87976386b7 in qemuProcessReconnect (opaque=0x7f87600db840) at qemu/qemu_process.c:3386
#5 0x00007f87bf6edfff in virThreadHelper (data=0x7f87600d5580) at util/virthread.c:206
#6 0x00007f87bb602334 in start_thread (arg=0x7f878ebda700) at pthread_create.c:333
#7 0x00007f87bb3481bd in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109
(gdb) frame 2
#2 0x00007f87bf6ecf95 in virSystemdGetMachineNameByPID (pid=9849) at util/virsystemd.c:228
228 dbus_message_unref(reply);
(gdb) p reply
$1 = (DBusMessage *) 0x0
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Spawning the pkcheck program every time a permission check is
required is hugely expensive on CPU. The pkcheck program is just
a dumb wrapper for the DBus API, so rewrite the code to use the
DBus API directly. This also simplifies error handling a bit.
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
