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[libvirt] [PATCH 2/2] qemu: deny privilege elevation and spawn in seccomp

Ján Tomko posted 2 patches 7 years, 1 month ago
[libvirt] [PATCH 2/2] qemu: deny privilege elevation and spawn in seccomp
Posted by Ján Tomko 7 years, 1 month ago 
If QEMU uses a seccomp blacklist (since 2.11), -sandbox on
no longer tries to whitelist all the calls, but uses sets
of blacklists:
default (always blacklisted with -sandbox on)
obsolete (defaults to deny)
elevateprivileges (setuid & co, default: allow)
spwan (fork & execve, default: allow)
resourcecontrol (setaffinity, setscheduler, default: allow)

If these are supported, default to sandbox with spawn and
elevateprivileges blacklisted.

https://bugzilla.redhat.com/show_bug.cgi?id=1492597

Signed-off-by: Ján Tomko <jtomko@redhat.com>
---
 src/qemu/qemu_command.c                     | 10 +++++++--
 tests/qemuxml2argvdata/minimal-sandbox.args | 25 +++++++++++++++++++++
 tests/qemuxml2argvdata/minimal-sandbox.xml  | 34 +++++++++++++++++++++++++++++
 tests/qemuxml2argvtest.c                    |  3 +++
 4 files changed, 70 insertions(+), 2 deletions(-)
 create mode 100644 tests/qemuxml2argvdata/minimal-sandbox.args
 create mode 100644 tests/qemuxml2argvdata/minimal-sandbox.xml

diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c
index 89fd08b64..3388f861a 100644
--- a/src/qemu/qemu_command.c
+++ b/src/qemu/qemu_command.c
@@ -10211,10 +10211,16 @@ qemuBuildCommandLine(virQEMUDriverPtr driver,
     }
 
     if (virQEMUCapsGet(qemuCaps, QEMU_CAPS_SECCOMP_SANDBOX)) {
-        if (cfg->seccompSandbox == 0)
+        if (cfg->seccompSandbox == 0) {
             virCommandAddArgList(cmd, "-sandbox", "off", NULL);
-        else if (cfg->seccompSandbox > 0)
+        } else if (virQEMUCapsGet(qemuCaps, QEMU_CAPS_SECCOMP_BLACKLIST) &&
+                   cfg->seccompSandbox != 0) {
+            virCommandAddArgList(cmd, "-sandbox",
+                                 "on,elevateprivileges=deny,spawn=deny", NULL);
+            /* obsolete=deny, resourcecontrol=allow */
+        } else if (cfg->seccompSandbox > 0) {
             virCommandAddArgList(cmd, "-sandbox", "on", NULL);
+        }
     } else if (cfg->seccompSandbox > 0) {
         virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
                        _("QEMU does not support seccomp sandboxes"));
diff --git a/tests/qemuxml2argvdata/minimal-sandbox.args b/tests/qemuxml2argvdata/minimal-sandbox.args
new file mode 100644
index 000000000..285cfed70
--- /dev/null
+++ b/tests/qemuxml2argvdata/minimal-sandbox.args
@@ -0,0 +1,25 @@
+LC_ALL=C \
+PATH=/bin \
+HOME=/home/test \
+USER=test \
+LOGNAME=test \
+QEMU_AUDIO_DRV=none \
+/usr/bin/qemu-system-i686 \
+-name QEMUGuest1 \
+-S \
+-M pc \
+-m 214 \
+-smp 1,sockets=1,cores=1,threads=1 \
+-uuid c7a5fdbd-edaf-9455-926a-d65c16db1809 \
+-nographic \
+-nodefaults \
+-chardev socket,id=charmonitor,path=/tmp/lib/domain--1-QEMUGuest1/monitor.sock,\
+server,nowait \
+-mon chardev=charmonitor,id=monitor,mode=readline \
+-no-acpi \
+-boot c \
+-usb \
+-drive file=/dev/HostVG/QEMUGuest1,format=raw,if=none,id=drive-ide0-0-0 \
+-device ide-drive,bus=ide.0,unit=0,drive=drive-ide0-0-0,id=ide0-0-0 \
+-device virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x3 \
+-sandbox on,elevateprivileges=deny,spawn=deny
diff --git a/tests/qemuxml2argvdata/minimal-sandbox.xml b/tests/qemuxml2argvdata/minimal-sandbox.xml
new file mode 100644
index 000000000..9ef92f8fe
--- /dev/null
+++ b/tests/qemuxml2argvdata/minimal-sandbox.xml
@@ -0,0 +1,34 @@
+<domain type='qemu'>
+  <name>QEMUGuest1</name>
+  <uuid>c7a5fdbd-edaf-9455-926a-d65c16db1809</uuid>
+  <title>A description of the test machine.</title>
+  <description>
+      A test of qemu&apos;s minimal configuration.
+      This test also tests the description and title elements.
+  </description>
+  <memory unit='KiB'>219100</memory>
+  <currentMemory unit='KiB'>219100</currentMemory>
+  <vcpu placement='static' cpuset='1-4,8-20,525'>1</vcpu>
+  <os>
+    <type arch='i686' machine='pc'>hvm</type>
+    <boot dev='hd'/>
+  </os>
+  <clock offset='utc'/>
+  <on_poweroff>destroy</on_poweroff>
+  <on_reboot>restart</on_reboot>
+  <on_crash>destroy</on_crash>
+  <devices>
+    <emulator>/usr/bin/qemu-system-i686</emulator>
+    <disk type='block' device='disk'>
+      <source dev='/dev/HostVG/QEMUGuest1'/>
+      <target dev='hda' bus='ide'/>
+      <address type='drive' controller='0' bus='0' target='0' unit='0'/>
+    </disk>
+    <controller type='usb' index='0'/>
+    <controller type='ide' index='0'/>
+    <controller type='pci' index='0' model='pci-root'/>
+    <input type='mouse' bus='ps2'/>
+    <input type='keyboard' bus='ps2'/>
+    <memballoon model='virtio'/>
+  </devices>
+</domain>
diff --git a/tests/qemuxml2argvtest.c b/tests/qemuxml2argvtest.c
index 308d71f72..5fb16987f 100644
--- a/tests/qemuxml2argvtest.c
+++ b/tests/qemuxml2argvtest.c
@@ -691,6 +691,9 @@ mymain(void)
     unsetenv("SDL_AUDIODRIVER");
 
     DO_TEST("minimal", NONE);
+    DO_TEST("minimal-sandbox",
+            QEMU_CAPS_SECCOMP_SANDBOX,
+            QEMU_CAPS_SECCOMP_BLACKLIST);
     DO_TEST_PARSE_ERROR("minimal-no-memory", NONE);
     DO_TEST("minimal-msg-timestamp", QEMU_CAPS_MSG_TIMESTAMP);
     DO_TEST("machine-aliases1", NONE);
-- 
2.13.6

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Re: [libvirt] [PATCH 2/2] qemu: deny privilege elevation and spawn in seccomp
Posted by Daniel P. Berrangé 7 years, 1 month ago 
On Sat, Mar 31, 2018 at 10:15:03PM +0200, Ján Tomko wrote:
> If QEMU uses a seccomp blacklist (since 2.11), -sandbox on
> no longer tries to whitelist all the calls, but uses sets
> of blacklists:
> default (always blacklisted with -sandbox on)
> obsolete (defaults to deny)

Perhaps list that anyway, so we don't rely on defaults.

> elevateprivileges (setuid & co, default: allow)
> spwan (fork & execve, default: allow)

s/spwan/spawn/

> resourcecontrol (setaffinity, setscheduler, default: allow)

I'm thinking we should blacklist resourcecontrol too perhaps, since libvirt
should be applying affinity/sched params itself.

> 
> If these are supported, default to sandbox with spawn and
> elevateprivileges blacklisted.
> 
> https://bugzilla.redhat.com/show_bug.cgi?id=1492597
> 
> Signed-off-by: Ján Tomko <jtomko@redhat.com>
> ---
>  src/qemu/qemu_command.c                     | 10 +++++++--
>  tests/qemuxml2argvdata/minimal-sandbox.args | 25 +++++++++++++++++++++
>  tests/qemuxml2argvdata/minimal-sandbox.xml  | 34 +++++++++++++++++++++++++++++
>  tests/qemuxml2argvtest.c                    |  3 +++
>  4 files changed, 70 insertions(+), 2 deletions(-)
>  create mode 100644 tests/qemuxml2argvdata/minimal-sandbox.args
>  create mode 100644 tests/qemuxml2argvdata/minimal-sandbox.xml
> 
> diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c
> index 89fd08b64..3388f861a 100644
> --- a/src/qemu/qemu_command.c
> +++ b/src/qemu/qemu_command.c
> @@ -10211,10 +10211,16 @@ qemuBuildCommandLine(virQEMUDriverPtr driver,
>      }
>  
>      if (virQEMUCapsGet(qemuCaps, QEMU_CAPS_SECCOMP_SANDBOX)) {
> -        if (cfg->seccompSandbox == 0)
> +        if (cfg->seccompSandbox == 0) {
>              virCommandAddArgList(cmd, "-sandbox", "off", NULL);
> -        else if (cfg->seccompSandbox > 0)
> +        } else if (virQEMUCapsGet(qemuCaps, QEMU_CAPS_SECCOMP_BLACKLIST) &&
> +                   cfg->seccompSandbox != 0) {

Ok this relies on fact that seccompSandbox defaults to '-1' if not present
in the config file, or can be set to 1 by the user.

> +            virCommandAddArgList(cmd, "-sandbox",
> +                                 "on,elevateprivileges=deny,spawn=deny", NULL);

> +            /* obsolete=deny, resourcecontrol=allow */

Yes, I'd suggest we add these too

> +        } else if (cfg->seccompSandbox > 0) {

So this is unreachable with new qemu

>              virCommandAddArgList(cmd, "-sandbox", "on", NULL);
> +        }
>      } else if (cfg->seccompSandbox > 0) {
>          virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
>                         _("QEMU does not support seccomp sandboxes"));
> diff --git a/tests/qemuxml2argvdata/minimal-sandbox.args b/tests/qemuxml2argvdata/minimal-sandbox.args
> new file mode 100644
> index 000000000..285cfed70
> --- /dev/null
> +++ b/tests/qemuxml2argvdata/minimal-sandbox.args
> @@ -0,0 +1,25 @@
> +LC_ALL=C \
> +PATH=/bin \
> +HOME=/home/test \
> +USER=test \
> +LOGNAME=test \
> +QEMU_AUDIO_DRV=none \
> +/usr/bin/qemu-system-i686 \
> +-name QEMUGuest1 \
> +-S \
> +-M pc \
> +-m 214 \
> +-smp 1,sockets=1,cores=1,threads=1 \
> +-uuid c7a5fdbd-edaf-9455-926a-d65c16db1809 \
> +-nographic \
> +-nodefaults \
> +-chardev socket,id=charmonitor,path=/tmp/lib/domain--1-QEMUGuest1/monitor.sock,\
> +server,nowait \
> +-mon chardev=charmonitor,id=monitor,mode=readline \
> +-no-acpi \
> +-boot c \
> +-usb \
> +-drive file=/dev/HostVG/QEMUGuest1,format=raw,if=none,id=drive-ide0-0-0 \
> +-device ide-drive,bus=ide.0,unit=0,drive=drive-ide0-0-0,id=ide0-0-0 \
> +-device virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x3 \
> +-sandbox on,elevateprivileges=deny,spawn=deny
> diff --git a/tests/qemuxml2argvdata/minimal-sandbox.xml b/tests/qemuxml2argvdata/minimal-sandbox.xml
> new file mode 100644
> index 000000000..9ef92f8fe
> --- /dev/null
> +++ b/tests/qemuxml2argvdata/minimal-sandbox.xml
> @@ -0,0 +1,34 @@
> +<domain type='qemu'>
> +  <name>QEMUGuest1</name>
> +  <uuid>c7a5fdbd-edaf-9455-926a-d65c16db1809</uuid>
> +  <title>A description of the test machine.</title>
> +  <description>
> +      A test of qemu&apos;s minimal configuration.
> +      This test also tests the description and title elements.
> +  </description>
> +  <memory unit='KiB'>219100</memory>
> +  <currentMemory unit='KiB'>219100</currentMemory>
> +  <vcpu placement='static' cpuset='1-4,8-20,525'>1</vcpu>
> +  <os>
> +    <type arch='i686' machine='pc'>hvm</type>
> +    <boot dev='hd'/>
> +  </os>
> +  <clock offset='utc'/>
> +  <on_poweroff>destroy</on_poweroff>
> +  <on_reboot>restart</on_reboot>
> +  <on_crash>destroy</on_crash>
> +  <devices>
> +    <emulator>/usr/bin/qemu-system-i686</emulator>
> +    <disk type='block' device='disk'>
> +      <source dev='/dev/HostVG/QEMUGuest1'/>
> +      <target dev='hda' bus='ide'/>
> +      <address type='drive' controller='0' bus='0' target='0' unit='0'/>
> +    </disk>
> +    <controller type='usb' index='0'/>
> +    <controller type='ide' index='0'/>
> +    <controller type='pci' index='0' model='pci-root'/>
> +    <input type='mouse' bus='ps2'/>
> +    <input type='keyboard' bus='ps2'/>
> +    <memballoon model='virtio'/>
> +  </devices>
> +</domain>
> diff --git a/tests/qemuxml2argvtest.c b/tests/qemuxml2argvtest.c
> index 308d71f72..5fb16987f 100644
> --- a/tests/qemuxml2argvtest.c
> +++ b/tests/qemuxml2argvtest.c
> @@ -691,6 +691,9 @@ mymain(void)
>      unsetenv("SDL_AUDIODRIVER");
>  
>      DO_TEST("minimal", NONE);
> +    DO_TEST("minimal-sandbox",
> +            QEMU_CAPS_SECCOMP_SANDBOX,
> +            QEMU_CAPS_SECCOMP_BLACKLIST);
>      DO_TEST_PARSE_ERROR("minimal-no-memory", NONE);
>      DO_TEST("minimal-msg-timestamp", QEMU_CAPS_MSG_TIMESTAMP);
>      DO_TEST("machine-aliases1", NONE);
> -- 
> 2.13.6
> 
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Regards,
Daniel
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