1 files changed, 112 insertions, 0 deletions

diff --git a/debian/patches/sshfp_with_server_cert b/debian/patches/sshfp_with_server_cert
new file mode 100644
index 000000000..7e6a489e6
--- /dev/null
+++ b/debian/patches/sshfp_with_server_cert
@@ -0,0 +1,112 @@
+From db4cdf7b763414af951c7f4031b10679c54d7988 Mon Sep 17 00:00:00 2001
+From: Matthew Vernon <mcv21@cam.ac.uk>
+Date: Tue, 25 Mar 2014 11:02:33 +0000
+Subject: Attempt SSHFP lookup even if server presents a certificate
+
+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>
+Bug-Debian: http://bugs.debian.org/742513
+Patch-Name: sshfp_with_server_cert
+---
+ sshconnect.c |   67 ++++++++++++++++++++++++++++++++++++++++------------------
+ 1 file changed, 47 insertions(+), 20 deletions(-)
+
+diff --git a/sshconnect.c b/sshconnect.c
+index 87c3770..b8510d2 100644
+--- a/sshconnect.c
++++ b/sshconnect.c
+@@ -1218,36 +1218,63 @@ 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,