openssh: fix for CVE-2014-2653

The verify_host_key function in sshconnect.c in the client in OpenSSH 6.6 and
earlier allows remote servers to trigger the skipping of SSHFP DNS RR checking
by presenting an unacceptable HostCertificate.

Signed-off-by: Chen Qi <Qi.Chen@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

2 files changed, 116 insertions, 1 deletions

diff --git a/meta/recipes-connectivity/openssh/openssh/openssh-CVE-2014-2653.patch b/meta/recipes-connectivity/openssh/openssh/openssh-CVE-2014-2653.patch
new file mode 100644
index 0000000000..674d186044
--- /dev/null
+++ b/meta/recipes-connectivity/openssh/openssh/openssh-CVE-2014-2653.patch
@@ -0,0 +1,114 @@
+Upstream-Status: Backport
+
+This CVE could be removed if openssh is upgrade to 6.6 or higher.
+Below are some details.
+
+Attempt SSHFP lookup even if server presents a certificate
+
+Reference:
+https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=742513
+
+If an ssh server presents a certificate to the client, then the client
+does not check the DNS for SSHFP records. This means that a malicious
+server can essentially disable DNS-host-key-checking, which means the
+client will fall back to asking the user (who will just say "yes" to
+the fingerprint, sadly).
+
+This patch means that the ssh client will, if necessary, extract the
+server key from the proffered certificate, and attempt to verify it
+against the DNS. The patch was written by Mark Wooding
+<mdw@distorted.org.uk>. I modified it to add one debug2 call, reviewed
+it, and tested it.
+
+Signed-off-by: Matthew Vernon <matthew@debian.org>
+Signed-off-by: Chen Qi <Qi.Chen@windriver.com>
+---
+--- a/sshconnect.c
++++ b/sshconnect.c
+@@ -1210,36 +1210,63 @@ fail:
+ 	return -1;
+ }
+ 
++static int
++check_host_key_sshfp(char *host, struct sockaddr *hostaddr, Key *host_key)
++{
++	int rc = -1;
++	int flags = 0;
++	Key *raw_key = NULL;
++
++	if (!options.verify_host_key_dns)
++		goto done;
++
++	/* XXX certs are not yet supported for DNS; try looking the raw key
++	 * up in the DNS anyway.
++	 */
++	if (key_is_cert(host_key)) {
++		debug2("Extracting key from cert for SSHFP lookup");
++		raw_key = key_from_private(host_key);
++		if (key_drop_cert(raw_key))
++			fatal("Couldn't drop certificate");
++		host_key = raw_key;
++	}
++
++	if (verify_host_key_dns(host, hostaddr, host_key, &flags))
++		goto done;
++
++	if (flags & DNS_VERIFY_FOUND) {
++
++		if (options.verify_host_key_dns == 1 &&
++				flags & DNS_VERIFY_MATCH &&
++				flags & DNS_VERIFY_SECURE) {
++			rc = 0;
++		} else if (flags & DNS_VERIFY_MATCH) {
++			matching_host_key_dns = 1;
++		} else {
++			warn_changed_key(host_key);
++			error("Update the SSHFP RR in DNS with the new "
++					"host key to get rid of this message.");
++		}
++	}
++
++done:
++	if (raw_key)
++		key_free(raw_key);
++	return rc;
++}
++
+ /* returns 0 if key verifies or -1 if key does NOT verify */
+ int
+ verify_host_key(char *host, struct sockaddr *hostaddr, Key *host_key)
+ {
+-	int flags = 0;
+ 	char *fp;
+ 
+ 	fp = key_fingerprint(host_key, SSH_FP_MD5, SSH_FP_HEX);
+ 	debug("Server host key: %s %s", key_type(host_key), fp);
+ 	free(fp);
+ 
+-	/* XXX certs are not yet supported for DNS */
+-	if (!key_is_cert(host_key) && options.verify_host_key_dns &&
+-	    verify_host_key_dns(host, hostaddr, host_key, &flags) == 0) {
+-		if (flags & DNS_VERIFY_FOUND) {
+-
+-			if (options.verify_host_key_dns == 1 &&
+-			    flags & DNS_VERIFY_MATCH &&
+-			    flags & DNS_VERIFY_SECURE)
+-				return 0;
+-
+-			if (flags & DNS_VERIFY_MATCH) {
+-				matching_host_key_dns = 1;
+-			} else {
+-				warn_changed_key(host_key);
+-				error("Update the SSHFP RR in DNS with the new "
+-				    "host key to get rid of this message.");
+-			}
+-		}
+-	}
++	if (check_host_key_sshfp(host, hostaddr, host_key) == 0)
++		return 0;
+ 
+ 	return check_host_key(host, hostaddr, options.port, host_key, RDRW,
+ 	    options.user_hostfiles, options.num_user_hostfiles,
+-- 
+1.7.9.5
+
diff --git a/meta/recipes-connectivity/openssh/openssh_6.5p1.bb b/meta/recipes-connectivity/openssh/openssh_6.5p1.bb
index 230f38ab31..795e085202 100644
--- a/meta/recipes-connectivity/openssh/openssh_6.5p1.bb
+++ b/meta/recipes-connectivity/openssh/openssh_6.5p1.bb
@@ -30,7 +30,8 @@ SRC_URI = "ftp://ftp.openbsd.org/pub/OpenBSD/OpenSSH/portable/openssh-${PV}.tar.
            file://volatiles.99_sshd \
            file://add-test-support-for-busybox.patch \
            file://run-ptest \
-           file://openssh-CVE-2014-2532.patch"
+           file://openssh-CVE-2014-2532.patch \
+           file://openssh-CVE-2014-2653.patch"
 
 PAM_SRC_URI = "file://sshd"