Re: [patch v2 1/1] virt-aa-helper: Add support for smartcard host-certificates

[Christian Ehrhardt <christian.ehrhardt@xxxxxxxxxxxxx>]

On Thu, Dec 5, 2019 at 6:25 PM Arnaud Patard <apatard@xxxxxxxxxxxxx> wrote:

When emulating smartcard with host certificates, qemu needs to
be able to read the certificates files. Add necessary code to
add the smartcard certificates file path to the apparmor profile.

Passthrough support has been tested with spicevmc and remote-viewer.

v2:
- Fix CodingStyle
- Add support for 'host' case.
- Add a comment to mention that the passthrough case doesn't need
  some configuration
- Use one rule with '{,*}' instead of two rules.

Signed-off-by: Arnaud Patard <apatard@xxxxxxxxxxxxx>
Index: libvirt/src/security/virt-aa-helper.c
===================================================================
--- libvirt.orig/src/security/virt-aa-helper.c
+++ libvirt/src/security/virt-aa-helper.c
@@ -1271,6 +1271,39 @@ get_files(vahControl * ctl)
         }
     }

+    for (i = 0; i < ctl->def->nsmartcards; i++) {
+        virDomainSmartcardDefPtr sc = ctl->def->smartcards[i];
+        virDomainSmartcardType sc_type = sc->type;
+        char *sc_db = (char *)VIR_DOMAIN_SMARTCARD_DEFAULT_DATABASE;
+        if (sc->data.cert.database)
+            sc_db = sc->data.cert.database;
+        switch (sc_type) {
+            /*
+             * Note: At time of writing, to get this working, qemu seccomp sandbox has
+             * to be disabled or the host must be running QEMU with commit
+             * 9a1565a03b79d80b236bc7cc2dbce52a2ef3a1b8.
+             * It's possibly due to libcacard:vcard_emul_new_event_thread(), which calls
+             * PR_CreateThread(), which calls {g,s}etpriority(). And resourcecontrol seccomp
+             * filter forbids it (cf src/qemu/qemu_command.c which seems to always use
+             * resourcecontrol=deny).
+             */
+            case VIR_DOMAIN_SMARTCARD_TYPE_HOST:
+                virBufferAddLit(&buf, "  \"/etc/pki/nssdb/{,*}\" rk,\n");

That path matches the examples in libvirt/qemu and also the fedora nss package

[root@fedora~]# rpm -qf /etc/pki/nssdb/
nss-3.47.0-2.fc29.x86_64

[root@fedora ~]# ll /etc/pki/nssdb/
total 8
-rw-r--r-- 1 root root 65536 Jan  6  2017 cert8.db
-rw-r--r-- 1 root root  9216 Jan  6  2017 cert9.db
-rw-r--r-- 1 root root 16384 Jan  6  2017 key3.db
-rw-r--r-- 1 root root 11264 Jan  6  2017 key4.db
-rw-r--r-- 1 root root   451 Oct 23 11:23 pkcs11.txt
-rw-r--r-- 1 root root 16384 Jan  6  2017 secmod.db

 

But on Debian/Ubuntu the paths are slightly different.

root@x:~# dpkg -L libnss3-nssdb
[...]
/var/lib/nssdb/key4.db
/var/lib/nssdb/cert9.db
/var/lib/nssdb/pkcs11.txt
/var/lib/nssdb/secmod.db

Therefore I'd ask you to add that path as well here.

+                break;
+            case VIR_DOMAIN_SMARTCARD_TYPE_HOST_CERTIFICATES:
+                virBufferAsprintf(&buf, "  \"%s/{,*}\" rk,\n", sc_db);
+                break;

From https://libvirt.org/formatdomain.html#elementsSmartcard

"An additional sub-element <database> can specify the absolute path to an alternate directory ... if not present, it defaults to /etc/pki/nssdb."

That is in "VIR_DOMAIN_SMARTCARD_DEFAULT_DATABASE".

Have you tested if sc_db is actually set to "VIR_DOMAIN_SMARTCARD_DEFAULT_DATABASE" in that case?

If it is e.g. undefined we need to check for that and add "VIR_DOMAIN_SMARTCARD_DEFAULT_DATABASE" instead.

Furthermore actually this lets us define:

  <smartcard mode='host-certificates'>
    <certificate>cert1</certificate>
    <certificate>cert2</certificate>
    <certificate>cert3</certificate>
    <database>/etc/pki/nssdb/</database>
  </smartcard>

There could be two guests using rather different cert[1-3] and there is no need letting them cross read right?

So instead of

  virBufferAsprintf(&buf, "  \"%s/{,*}\" rk,\n", sc_db);

maybe something like this is safer:

iterate on certs-that-are-defined => cert

    virBufferAsprintf(&buf, "  \"%s/%s\" rk,\n", sc_db, cert);

 

+            /*
+             * Nothing to do for passthrough, as the smartcard
+             * access is done through TCP or Spice
+             */
+            case VIR_DOMAIN_SMARTCARD_TYPE_PASSTHROUGH:
+                break;
+            case VIR_DOMAIN_SMARTCARD_TYPE_LAST:
+                break;
+        }
+    }
+
     if (ctl->def->virtType == VIR_DOMAIN_VIRT_KVM) {
         for (i = 0; i < ctl->def->nnets; i++) {
             virDomainNetDefPtr net = ctl->def->nets[i];

--

Christian Ehrhardt
Staff Engineer, Ubuntu Server
Canonical Ltd

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