[PATCH] apparmor: Workaround for unconfined libvirtd when triggered by unprivileged user

[Stefano Brivio <sbrivio@redhat.com>]

If libvirtd is triggered by an unprivileged user, the virt-aa-helper
mechanism doesn't work, because per-VM profiles can't be instantiated,
and as a result libvirtd runs unconfined.

This means passt can't start, because the passt subprofile from
libvirt's profile is not loaded either.

Example:

  $ virsh start alpine
  error: Failed to start domain 'alpine'
  error: internal error: Child process (passt --one-off --socket /run/user/1000/libvirt/qemu/run/passt/1-alpine-net0.socket --pid /run/user/1000/libvirt/qemu/run/passt/1-alpine-net0-passt.pid --tcp-ports 40922:2) unexpected fatal signal 11

Add an annoying workaround for the moment being. Much better than
encouraging users to start guests as root, or to disable AppArmor
altogether.

Reported-by: Prafulla Giri <prafulla.giri@protonmail.com>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
---
 contrib/apparmor/usr.bin.passt | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/contrib/apparmor/usr.bin.passt b/contrib/apparmor/usr.bin.passt
index 9568189..62a4514 100644
--- a/contrib/apparmor/usr.bin.passt
+++ b/contrib/apparmor/usr.bin.passt
@@ -27,4 +27,25 @@ profile passt /usr/bin/passt{,.avx2} {
 
   owner @{HOME}/**			w,	# pcap(), pidfile_open(),
 						# pidfile_write()
+
+  # Workaround: libvirt's profile comes with a passt subprofile which includes,
+  # in turn, <abstractions/passt>, and adds libvirt-specific rules on top, to
+  # allow passt (when started by libvirtd) to write socket and PID files in the
+  # location requested by libvirtd itself, and to execute passt itself.
+  #
+  # However, when libvirt runs as unprivileged user, the mechanism based on
+  # virt-aa-helper, designed to build per-VM profiles as guests are started,
+  # doesn't work. The helper needs to create and load profiles on the fly, which
+  # can't be done by unprivileged users, of course.
+  #
+  # As a result, libvirtd runs unconfined if guests are started by unprivileged
+  # users, starting passt unconfined as well, which means that passt runs under
+  # its own stand-alone profile (this one), which implies in turn that execve()
+  # of /usr/bin/passt is not allowed, and socket and PID files can't be written.
+  #
+  # Duplicate libvirt-specific rules here as long as this is not solved in
+  # libvirt's profile itself.
+  /usr/bin/passt r,
+  owner @{run}/user/[0-9]*/libvirt/qemu/run/passt/* rw,
+  owner @{run}/libvirt/qemu/passt/* rw,
 }
-- 
@@ -27,4 +27,25 @@ profile passt /usr/bin/passt{,.avx2} {
 
   owner @{HOME}/**			w,	# pcap(), pidfile_open(),
 						# pidfile_write()
+
+  # Workaround: libvirt's profile comes with a passt subprofile which includes,
+  # in turn, <abstractions/passt>, and adds libvirt-specific rules on top, to
+  # allow passt (when started by libvirtd) to write socket and PID files in the
+  # location requested by libvirtd itself, and to execute passt itself.
+  #
+  # However, when libvirt runs as unprivileged user, the mechanism based on
+  # virt-aa-helper, designed to build per-VM profiles as guests are started,
+  # doesn't work. The helper needs to create and load profiles on the fly, which
+  # can't be done by unprivileged users, of course.
+  #
+  # As a result, libvirtd runs unconfined if guests are started by unprivileged
+  # users, starting passt unconfined as well, which means that passt runs under
+  # its own stand-alone profile (this one), which implies in turn that execve()
+  # of /usr/bin/passt is not allowed, and socket and PID files can't be written.
+  #
+  # Duplicate libvirt-specific rules here as long as this is not solved in
+  # libvirt's profile itself.
+  /usr/bin/passt r,
+  owner @{run}/user/[0-9]*/libvirt/qemu/run/passt/* rw,
+  owner @{run}/libvirt/qemu/passt/* rw,
 }
-- 
2.43.0