openssh: fix for read-only rootfs

If the rootfs is read-only and the ssh keys are not available at system
start-up, the init script will generate ssh keys into /etc/ssh, thus
causing a 'read-only file system' error.

In order for Yocto based image to work correctly for read-only rootfs,
we use the following logic for openssh.

If the rootfs is read-only and there are pre-generated keys under /etc/ssh,
we use the pre-generated keys. Note the pre-generated keys are mainly for
debugging or development purpose.
If the rootfs is read-only and there are no pre-generated keys under
/etc/ssh, we use /var/run/ssh as the location for ssh keys. That is, at
system boot-up, the generated ssh keys will put into /var/run/ssh.

[YOCTO #4887]

(From OE-Core rev: 2ed44745024f04aa4e00ddba3009153c6b47c8e9)

Signed-off-by: Chen Qi <Qi.Chen@windriver.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

1 files changed, 12 insertions, 0 deletions

diff --git a/meta/classes/image.bbclass b/meta/classes/image.bbclass
index 494664627d..116bd226ea 100644
--- a/meta/classes/image.bbclass
+++ b/meta/classes/image.bbclass
@@ -262,6 +262,18 @@ read_only_rootfs_hook () {
                 if [ -x ${IMAGE_ROOTFS}/etc/init.d/populate-volatile.sh ]; then
                         ${IMAGE_ROOTFS}/etc/init.d/populate-volatile.sh
                 fi
+                # If we're using openssh and the /etc/ssh directory has no pre-generated keys,
+                # we should configure openssh to use the configuration file /etc/ssh/sshd_config_readonly
+                # and the keys under /var/run/ssh.
+                if [ -d ${IMAGE_ROOTFS}/etc/ssh ]; then
+                        if [ -e ${IMAGE_ROOTFS}/etc/ssh/ssh_host_rsa_key ]; then
+                                echo "SYSCONFDIR=/etc/ssh" >> ${IMAGE_ROOTFS}/etc/default/ssh
+                                echo "SSHD_OPTS=" >> ${IMAGE_ROOTFS}/etc/default/ssh
+                        else
+                                echo "SYSCONFDIR=/var/run/ssh" >> ${IMAGE_ROOTFS}/etc/default/ssh
+                                echo "SSHD_OPTS='-f /etc/ssh/sshd_config_readonly'" >> ${IMAGE_ROOTFS}/etc/default/ssh
+                        fi
+                fi
         fi
 }