openssh: drop sshd support for DSA host keys

PATCH In review Andre McCurdy 2 participants 4 messages May 25, 2018 – Jun 4, 2018

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Andre McCurdy

author

2018-05-25 22:07 UTC #0 lore raw

PATCH 1/1 openssh: drop sshd support for DSA host keys

DSA keys have been deprecated for some time:

https://www.gentoo.org/support/news-items/2015-08-13-openssh-weak-keys.html

Signed-off-by Andre McCurdy <[email protected]>

---
 meta/recipes-connectivity/openssh/openssh/sshd_check_keys | 8 --------
 meta/recipes-connectivity/openssh/openssh/sshd_config     | 1 -
 meta/recipes-connectivity/openssh/openssh_7.6p1.bb        | 1 -
 3 files changed, 10 deletions(-)

meta/recipes-connectivity/openssh/openssh/sshd_check_keys +0 -8

index 5463b1a..be2e2ec 100644
@@ -60,9 +60,6 @@ done
 HOST_KEY_RSA=$(grep ^HostKey "${sshd_config}" | grep _rsa_ | tail -1 | awk ' { print $2 } ')
 [ -z "${HOST_KEY_RSA}" ] && HOST_KEY_RSA=$(grep HostKey "${sshd_config}" | grep _rsa_ | tail -1 | awk ' { print $2 } ')
 [ -z "${HOST_KEY_RSA}" ] && HOST_KEY_RSA=$SYSCONFDIR/ssh_host_rsa_key
-HOST_KEY_DSA=$(grep ^HostKey "${sshd_config}" | grep _dsa_ | tail -1 | awk ' { print $2 } ')
-[ -z "${HOST_KEY_DSA}" ] && HOST_KEY_DSA=$(grep HostKey "${sshd_config}" | grep _dsa_ | tail -1 | awk ' { print $2 } ')
-[ -z "${HOST_KEY_DSA}" ] && HOST_KEY_DSA=$SYSCONFDIR/ssh_host_dsa_key
 HOST_KEY_ECDSA=$(grep ^HostKey "${sshd_config}" | grep _ecdsa_ | tail -1 | awk ' { print $2 } ')
 [ -z "${HOST_KEY_ECDSA}" ] && HOST_KEY_ECDSA=$(grep HostKey "${sshd_config}" | grep _ecdsa_ | tail -1 | awk ' { print $2 } ')
 [ -z "${HOST_KEY_ECDSA}" ] && HOST_KEY_ECDSA=$SYSCONFDIR/ssh_host_ecdsa_key

@@ -79,12 +76,7 @@ if [ ! -f $HOST_KEY_ECDSA ]; then
     echo "  generating ssh ECDSA key..."
     generate_key $HOST_KEY_ECDSA ecdsa
 fi
-if [ ! -f $HOST_KEY_DSA ]; then
-    echo "  generating ssh DSA key..."
-    generate_key $HOST_KEY_DSA dsa
-fi
 if [ ! -f $HOST_KEY_ED25519 ]; then
     echo "  generating ssh ED25519 key..."
     generate_key $HOST_KEY_ED25519 ed25519
 fi
-

meta/recipes-connectivity/openssh/openssh/sshd_config +0 -1

index 31fe5d9..b7c3ccd 100644
@@ -22,7 +22,6 @@ Protocol 2
 #HostKey /etc/ssh/ssh_host_key
 # HostKeys for protocol version 2
 #HostKey /etc/ssh/ssh_host_rsa_key
-#HostKey /etc/ssh/ssh_host_dsa_key
 #HostKey /etc/ssh/ssh_host_ecdsa_key
 #HostKey /etc/ssh/ssh_host_ed25519_key

meta/recipes-connectivity/openssh/openssh_7.6p1.bb +0 -1

index e11e8d7..a527a7c 100644
@@ -110,7 +110,6 @@ do_install_append () {
 	install -m 644 ${D}${sysconfdir}/ssh/sshd_config ${D}${sysconfdir}/ssh/sshd_config_readonly
 	sed -i '/HostKey/d' ${D}${sysconfdir}/ssh/sshd_config_readonly
 	echo "HostKey /var/run/ssh/ssh_host_rsa_key" >> ${D}${sysconfdir}/ssh/sshd_config_readonly
-	echo "HostKey /var/run/ssh/ssh_host_dsa_key" >> ${D}${sysconfdir}/ssh/sshd_config_readonly
 	echo "HostKey /var/run/ssh/ssh_host_ecdsa_key" >> ${D}${sysconfdir}/ssh/sshd_config_readonly
 	echo "HostKey /var/run/ssh/ssh_host_ed25519_key" >> ${D}${sysconfdir}/ssh/sshd_config_readonly

Signature · 1 line

1.9.1

Mark Hatle

2018-06-04 22:26 UTC #2 lore raw

Quoted 8 lines · Andre McCurdy

Quoted 3 lines · Andre McCurdy
DSA keys have been deprecated for some time:
https://www.gentoo.org/support/news-items/2015-08-13-openssh-weak-keys.html
Ping.
Any issues with this?

At Wind River we have a series of patches to disable weak-ciphers. We had globally disabled them a while back and found that a number of applications and customers still were using them for various things.

Even though they were 'weak', they were still needed.

See:

https://github.com/WindRiver-OpenSourceLabs/wrlinux/tree/master-wr/wrlinux-distro/recipes-weak-ciphers

If this work is something that should be submitted to oe-core/meta-openembedded and would be a candidate for merging, I'm all for it.

My suggestion though would be to reverse the checks we have.. instead of a distro feature of 'openssl-no-weak-ciphers', make it 'allow-weak-ciphers', and disable them by default.

A few things like Kerberos, freeradius and others require weak ciphers for some functions. So the corresponding patches for those would need to be developed.

If this is something we want to do, then the OpenSSH change below could be switched into a PACKAGECONFIG option, and still allow people to define an insecure system -- if they need to...

--Mark

Quoted 61 lines

Signed-off-by Andre McCurdy <[email protected]>

---
 meta/recipes-connectivity/openssh/openssh/sshd_check_keys | 8 --------
 meta/recipes-connectivity/openssh/openssh/sshd_config     | 1 -
 meta/recipes-connectivity/openssh/openssh_7.6p1.bb        | 1 -
 3 files changed, 10 deletions(-)

meta/recipes-connectivity/openssh/openssh/sshd_check_keys +0 -8

index 5463b1a..be2e2ec 100644
@@ -60,9 +60,6 @@ done
 HOST_KEY_RSA=$(grep ^HostKey "${sshd_config}" | grep _rsa_ | tail -1 | awk ' { print $2 } ')
 [ -z "${HOST_KEY_RSA}" ] && HOST_KEY_RSA=$(grep HostKey "${sshd_config}" | grep _rsa_ | tail -1 | awk ' { print $2 } ')
 [ -z "${HOST_KEY_RSA}" ] && HOST_KEY_RSA=$SYSCONFDIR/ssh_host_rsa_key
-HOST_KEY_DSA=$(grep ^HostKey "${sshd_config}" | grep _dsa_ | tail -1 | awk ' { print $2 } ')
-[ -z "${HOST_KEY_DSA}" ] && HOST_KEY_DSA=$(grep HostKey "${sshd_config}" | grep _dsa_ | tail -1 | awk ' { print $2 } ')
-[ -z "${HOST_KEY_DSA}" ] && HOST_KEY_DSA=$SYSCONFDIR/ssh_host_dsa_key
 HOST_KEY_ECDSA=$(grep ^HostKey "${sshd_config}" | grep _ecdsa_ | tail -1 | awk ' { print $2 } ')
 [ -z "${HOST_KEY_ECDSA}" ] && HOST_KEY_ECDSA=$(grep HostKey "${sshd_config}" | grep _ecdsa_ | tail -1 | awk ' { print $2 } ')
 [ -z "${HOST_KEY_ECDSA}" ] && HOST_KEY_ECDSA=$SYSCONFDIR/ssh_host_ecdsa_key

@@ -79,12 +76,7 @@ if [ ! -f $HOST_KEY_ECDSA ]; then
     echo "  generating ssh ECDSA key..."
     generate_key $HOST_KEY_ECDSA ecdsa
 fi
-if [ ! -f $HOST_KEY_DSA ]; then
-    echo "  generating ssh DSA key..."
-    generate_key $HOST_KEY_DSA dsa
-fi
 if [ ! -f $HOST_KEY_ED25519 ]; then
     echo "  generating ssh ED25519 key..."
     generate_key $HOST_KEY_ED25519 ed25519
 fi
-

meta/recipes-connectivity/openssh/openssh/sshd_config +0 -1

index 31fe5d9..b7c3ccd 100644
@@ -22,7 +22,6 @@ Protocol 2
 #HostKey /etc/ssh/ssh_host_key
 # HostKeys for protocol version 2
 #HostKey /etc/ssh/ssh_host_rsa_key
-#HostKey /etc/ssh/ssh_host_dsa_key
 #HostKey /etc/ssh/ssh_host_ecdsa_key
 #HostKey /etc/ssh/ssh_host_ed25519_key

meta/recipes-connectivity/openssh/openssh_7.6p1.bb +0 -2

index e11e8d7..a527a7c 100644
@@ -110,7 +110,6 @@ do_install_append () {
        install -m 644 ${D}${sysconfdir}/ssh/sshd_config ${D}${sysconfdir}/ssh/sshd_config_readonly
        sed -i '/HostKey/d' ${D}${sysconfdir}/ssh/sshd_config_readonly
        echo "HostKey /var/run/ssh/ssh_host_rsa_key" >> ${D}${sysconfdir}/ssh/sshd_config_readonly
-       echo "HostKey /var/run/ssh/ssh_host_dsa_key" >> ${D}${sysconfdir}/ssh/sshd_config_readonly
        echo "HostKey /var/run/ssh/ssh_host_ecdsa_key" >> ${D}${sysconfdir}/ssh/sshd_config_readonly
        echo "HostKey /var/run/ssh/ssh_host_ed25519_key" >> ${D}${sysconfdir}/ssh/sshd_config_readonly
 
--

1.9.1

Andre McCurdy

author

2018-06-04 23:22 UTC #3 lore raw

Quoted 14 lines · Mark Hatle

Quoted 8 lines · Andre McCurdy
Quoted 3 lines · Andre McCurdy
DSA keys have been deprecated for some time:
https://www.gentoo.org/support/news-items/2015-08-13-openssh-weak-keys.html
Ping.
Any issues with this?
At Wind River we have a series of patches to disable weak-ciphers. We had globally disabled them a while back and found that a number of applications and customers still were using them for various things.

Quoted 5 lines

Even though they were 'weak', they were still needed.
See:
https://github.com/WindRiver-OpenSourceLabs/wrlinux/tree/master-wr/wrlinux-distro/recipes-weak-ciphers

Disabling weak ciphers in openssl and then fixing the fallout in *everything* that links with openssl is quite a different and more ambitious undertaking.

For ssh host key formats, the only requirement is that host and client agree on at least one common format. RSA is the most common and well established so as long as we don't disable that, disabling support for less common or less secure formats is unlikely to cause any issues.

Currently for the dropbear ssh server we ONLY enable RSA host keys and that seems to be working out fine.

Having our openssh server drop support for DSA host keys seems like the right thing to do given potential security concerns and the fact that modern ssh clients (e.g. openssh after 7.0p1 from 2015) don't support them any more.

Quoted 78 lines

If this work is something that should be submitted to oe-core/meta-openembedded and would be a candidate for merging, I'm all for it.

My suggestion though would be to reverse the checks we have.. instead of a distro feature of 'openssl-no-weak-ciphers', make it 'allow-weak-ciphers', and disable them by default.

A few things like Kerberos, freeradius and others require weak ciphers for some functions. So the corresponding patches for those would need to be developed.

If this is something we want to do, then the OpenSSH change below could be switched into a PACKAGECONFIG option, and still allow people to define an insecure system -- if they need to...

--Mark

Quoted 61 lines

Signed-off-by Andre McCurdy <[email protected]>

---
 meta/recipes-connectivity/openssh/openssh/sshd_check_keys | 8 --------
 meta/recipes-connectivity/openssh/openssh/sshd_config     | 1 -
 meta/recipes-connectivity/openssh/openssh_7.6p1.bb        | 1 -
 3 files changed, 10 deletions(-)

meta/recipes-connectivity/openssh/openssh/sshd_check_keys +0 -8

index 5463b1a..be2e2ec 100644
@@ -60,9 +60,6 @@ done
 HOST_KEY_RSA=$(grep ^HostKey "${sshd_config}" | grep _rsa_ | tail -1 | awk ' { print $2 } ')
 [ -z "${HOST_KEY_RSA}" ] && HOST_KEY_RSA=$(grep HostKey "${sshd_config}" | grep _rsa_ | tail -1 | awk ' { print $2 } ')
 [ -z "${HOST_KEY_RSA}" ] && HOST_KEY_RSA=$SYSCONFDIR/ssh_host_rsa_key
-HOST_KEY_DSA=$(grep ^HostKey "${sshd_config}" | grep _dsa_ | tail -1 | awk ' { print $2 } ')
-[ -z "${HOST_KEY_DSA}" ] && HOST_KEY_DSA=$(grep HostKey "${sshd_config}" | grep _dsa_ | tail -1 | awk ' { print $2 } ')
-[ -z "${HOST_KEY_DSA}" ] && HOST_KEY_DSA=$SYSCONFDIR/ssh_host_dsa_key
 HOST_KEY_ECDSA=$(grep ^HostKey "${sshd_config}" | grep _ecdsa_ | tail -1 | awk ' { print $2 } ')
 [ -z "${HOST_KEY_ECDSA}" ] && HOST_KEY_ECDSA=$(grep HostKey "${sshd_config}" | grep _ecdsa_ | tail -1 | awk ' { print $2 } ')
 [ -z "${HOST_KEY_ECDSA}" ] && HOST_KEY_ECDSA=$SYSCONFDIR/ssh_host_ecdsa_key

@@ -79,12 +76,7 @@ if [ ! -f $HOST_KEY_ECDSA ]; then
     echo "  generating ssh ECDSA key..."
     generate_key $HOST_KEY_ECDSA ecdsa
 fi
-if [ ! -f $HOST_KEY_DSA ]; then
-    echo "  generating ssh DSA key..."
-    generate_key $HOST_KEY_DSA dsa
-fi
 if [ ! -f $HOST_KEY_ED25519 ]; then
     echo "  generating ssh ED25519 key..."
     generate_key $HOST_KEY_ED25519 ed25519
 fi
-

meta/recipes-connectivity/openssh/openssh/sshd_config +0 -1

index 31fe5d9..b7c3ccd 100644
@@ -22,7 +22,6 @@ Protocol 2
 #HostKey /etc/ssh/ssh_host_key
 # HostKeys for protocol version 2
 #HostKey /etc/ssh/ssh_host_rsa_key
-#HostKey /etc/ssh/ssh_host_dsa_key
 #HostKey /etc/ssh/ssh_host_ecdsa_key
 #HostKey /etc/ssh/ssh_host_ed25519_key

meta/recipes-connectivity/openssh/openssh_7.6p1.bb +0 -2

index e11e8d7..a527a7c 100644
@@ -110,7 +110,6 @@ do_install_append () {
        install -m 644 ${D}${sysconfdir}/ssh/sshd_config ${D}${sysconfdir}/ssh/sshd_config_readonly
        sed -i '/HostKey/d' ${D}${sysconfdir}/ssh/sshd_config_readonly
        echo "HostKey /var/run/ssh/ssh_host_rsa_key" >> ${D}${sysconfdir}/ssh/sshd_config_readonly
-       echo "HostKey /var/run/ssh/ssh_host_dsa_key" >> ${D}${sysconfdir}/ssh/sshd_config_readonly
        echo "HostKey /var/run/ssh/ssh_host_ecdsa_key" >> ${D}${sysconfdir}/ssh/sshd_config_readonly
        echo "HostKey /var/run/ssh/ssh_host_ed25519_key" >> ${D}${sysconfdir}/ssh/sshd_config_readonly
 
--

1.9.1