seccomp: extend manpage, and add examples

doc/examples/Makefile.am

@@ -8,7 +8,10 @@ pkgexamples_DATA = \
 	lxc-empty-netns.conf \
 	lxc-phys.conf \
 	lxc-veth.conf \
-	lxc-complex.conf
+	lxc-complex.conf \
+	seccomp-v1.conf \
+	seccomp-v2-blacklist.conf \
+	seccomp-v2.conf
 endif
 
 noinst_DATA = \
@@ -18,4 +21,7 @@ noinst_DATA = \
 	lxc-no-netns.conf.in \
 	lxc-phys.conf.in \
 	lxc-veth.conf.in \
-	lxc-complex.conf.in
+	lxc-complex.conf.in \
+	seccomp-v1.conf \
+	seccomp-v2-blacklist.conf \
+	seccomp-v2.conf

doc/examples/seccomp-v1.conf

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doc/examples/seccomp-v2-blacklist.conf

+2
+blacklist
+# v2 allows comments after the second line, with '#' in first column,
+# blacklist will allow syscalls by default
+# if 'errno 0' was not appended to 'mknod' below, then the task would
+# simply be killed when it tried to mknod.  'errno 0' means do not allow
+# the container to mknod, but immediately return 0.
+mknod errno 0

doc/examples/seccomp-v2.conf

+2
+whitelist trap
+# 'whitelist' would normally mean kill a task doing any syscall which is not
+# whitelisted below.  By appending 'trap' to the line, we will cause a SIGSYS
+# to be sent to the task instead.  'errno 0' would  mean don't allow the system
+# call but immediately return 0.  'errno 22' would mean return EINVAL immediately.
+[x86_64]
+open
+close
+read
+write
+mount
+umount2
+# Since we are listing system calls by name, we can also ask to have them resolved
+# for another arch, i.e. for 32/64-bit versions.
+[x86]
+open
+close
+read
+write
+mount
+umount2
+# Do note that this policy does not whitelist enough system calls to allow a
+# system container to boot.

doc/lxc.container.conf.sgml.in

@@ -1015,11 +1015,33 @@ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
       <para>
         A container can be started with a reduced set of available
 	system calls by loading a seccomp profile at startup.  The
-	seccomp configuration file should begin with a version number
-	(which currently must be 1) on the first line, a policy type
-	(which must be 'whitelist') on the second line, followed by a
-	list of allowed system call numbers, one per line.
+	seccomp configuration file must begin with a version number
+	on the first line, a policy type on the second line, followed
+	by the configuration.
       </para>
+      <para>
+        Versions 1 and 2 are currently supported.  In version 1, the
+	policy is a simple whitelist.  The second line therefore must
+	read "whitelist", with the rest of the file containing one (numeric)
+	sycall number per line.  Each syscall number is whitelisted,
+	while every unlisted number is blacklisted for use in teh container
+      </para>
+
+      <para>
+       In version 2, the policy may be blacklist or whitelist,
+       supports per-rule and per-policy default actions, and supports
+       per-architecture system call resolution from textual names.
+      </para>
+      <para>
+       An example blacklist policy, in which all system calls are
+       allowed except for mknod, which will simply do nothing and
+       return 0 (success), looks like:
+      </para>
+<screen>
+2
+blacklist
+mknod errno 0
+</screen>
       <variablelist>
 	<varlistentry>
 	  <term>