hw/9pfs: man page for proxy helper

Signed-off-by: M. Mohan Kumar <mohan@in.ibm.com>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>

Makefile

@@ -38,6 +38,7 @@ LIBS+=-lz $(LIBS_TOOLS)
 
 ifdef BUILD_DOCS
 DOCS=qemu-doc.html qemu-tech.html qemu.1 qemu-img.1 qemu-nbd.8 QMP/qmp-commands.txt
+DOCS+=fsdev/virtfs-proxy-helper.1
 else
 DOCS=
 endif
@@ -289,7 +290,10 @@ ifdef CONFIG_POSIX
 	$(INSTALL_DIR) "$(DESTDIR)$(mandir)/man8"
 	$(INSTALL_DATA) qemu-nbd.8 "$(DESTDIR)$(mandir)/man8"
 endif
-
+ifdef CONFIG_VIRTFS
+	$(INSTALL_DIR) "$(DESTDIR)$(mandir)/man1"
+	$(INSTALL_DATA) fsdev/virtfs-proxy-helper.1 "$(DESTDIR)$(mandir)/man1"
+endif
 install-sysconfig:
 	$(INSTALL_DIR) "$(DESTDIR)$(sysconfdir)/qemu"
 	$(INSTALL_DATA) $(SRC_PATH)/sysconfigs/target/target-x86_64.conf "$(DESTDIR)$(sysconfdir)/qemu"
@@ -373,6 +377,12 @@ qemu-img.1: qemu-img.texi qemu-img-cmds.texi
 	  pod2man --section=1 --center=" " --release=" " qemu-img.pod > $@, \
 	  "  GEN   $@")
 
+fsdev/virtfs-proxy-helper.1: fsdev/virtfs-proxy-helper.texi
+	$(call quiet-command, \
+	  perl -Ww -- $(SRC_PATH)/scripts/texi2pod.pl $< fsdev/virtfs-proxy-helper.pod && \
+	  pod2man --section=1 --center=" " --release=" " fsdev/virtfs-proxy-helper.pod > $@, \
+	  "  GEN   $@")
+
 qemu-nbd.8: qemu-nbd.texi
 	$(call quiet-command, \
 	  perl -Ww -- $(SRC_PATH)/scripts/texi2pod.pl $< qemu-nbd.pod && \

fsdev/virtfs-proxy-helper.texi

+@example
+@c man begin SYNOPSIS
+usage: virtfs-proxy-helper options
+@c man end
+@end example
+
+@c man begin DESCRIPTION
+@table @description
+Pass-through security model in QEMU 9p server needs root privilege to do
+few file operations (like chown, chmod to any mode/uid:gid).  There are two
+issues in pass-through security model
+
+1) TOCTTOU vulnerability: Following symbolic links in the server could
+provide access to files beyond 9p export path.
+
+2) Running QEMU with root privilege could be a security issue.
+
+To overcome above issues, following approach is used: A new filesytem
+type 'proxy' is introduced. Proxy FS uses chroot + socket combination
+for securing the vulnerability known with following symbolic links.
+Intention of adding a new filesystem type is to allow qemu to run
+in non-root mode, but doing privileged operations using socket IO.
+
+Proxy helper(a stand alone binary part of qemu) is invoked with
+root privileges. Proxy helper chroots into 9p export path and creates
+a socket pair or a named socket based on the command line parameter.
+Qemu and proxy helper communicate using this socket. QEMU proxy fs
+driver sends filesystem request to proxy helper and receives the
+response from it.
+
+Proxy helper is designed so that it can drop the root privilege with
+retaining capbilities needed for doing filesystem operations only.
+
+@end table
+@c man end
+
+@c man begin OPTIONS
+The following options are supported:
+@table @option
+@item -h
+@findex -h
+Display help and exit
+@item -p|--path path
+Path to export for proxy filesystem driver
+@item -f|--fd socket-id
+Use given file descriptor as socket descriptor for communicating with
+qemu proxy fs drier. Usually a helper like libvirt will create
+socketpair and pass one of the fds as parameter to -f|--fd
+@item -n|--nodaemon
+Run as a normal program. By default program will run in daemon mode
+@end table
+@c man end
+
+@setfilename virtfs-proxy-helper
+@settitle QEMU 9p virtfs proxy filesystem helper
+
+@c man begin AUTHOR
+M. Mohan Kumar
+@c man end