openssh-unix-dev May 2011 archive
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openssh-unix-dev: Re: backdoor by authorized_keys2 leftovers

Re: backdoor by authorized_keys2 leftovers

From: Damien Miller <djm_at_nospam>
Date: Fri May 20 2011 - 08:49:19 GMT
To: Darren Tucker <dtucker@zip.com.au>

... and here is the regress part (with some fixes for existing races)

Index: cfgmatch.sh
===================================================================
RCS file: /cvs/src/regress/usr.bin/ssh/cfgmatch.sh,v
retrieving revision 1.4
diff -u -p -r1.4 cfgmatch.sh
--- cfgmatch.sh 13 Dec 2006 08:36:36 -0000 1.4
+++ cfgmatch.sh 20 May 2011 08:48:09 -0000
@@ -7,21 +7,47 @@ pidfile=$OBJ/remote_pid
 fwdport=3301
 fwd="-L $fwdport:127.0.0.1:$PORT"
 
+echo "ExitOnForwardFailure=yes" >> ssh_config
+echo "ExitOnForwardFailure=yes" >> ssh_proxy
+
+start_client()
+{
+ rm -f $pidfile
+ ${SSH} -q -$p $fwd "$@" somehost \
+ exec sh -c \'"echo \$\$ > $pidfile; exec sleep 100"\' \
+ >>$TEST_SSH_LOGFILE 2>&1 &
+ client_pid=$!
+ # Wait for remote end
+ n=0
+ while test ! -f $pidfile ; do
+ sleep 1
+ n=`expr $n + 1`
+ if test $n -gt 60; then
+ kill $client_pid
+ fatal "timeout waiting for background ssh"
+ fi
+ done
+}
+
 stop_client()
 {
         pid=`cat $pidfile`
         if [ ! -z "$pid" ]; then
                 kill $pid
         fi
+ wait
 }
 
 cp $OBJ/sshd_proxy $OBJ/sshd_proxy_bak
-
 echo "PermitOpen 127.0.0.1:1" >>$OBJ/sshd_config
 echo "Match Address 127.0.0.1" >>$OBJ/sshd_config
 echo "PermitOpen 127.0.0.1:$PORT" >>$OBJ/sshd_config
 
+grep -v AuthorizedKeysFile $OBJ/sshd_proxy_bak > $OBJ/sshd_proxy
+echo "AuthorizedKeysFile /dev/null" >>$OBJ/sshd_proxy
 echo "PermitOpen 127.0.0.1:1" >>$OBJ/sshd_proxy
+echo "Match user $USER" >>$OBJ/sshd_proxy
+echo "AuthorizedKeysFile /dev/null $OBJ/authorized_keys_%u" >>$OBJ/sshd_proxy
 echo "Match Address 127.0.0.1" >>$OBJ/sshd_proxy
 echo "PermitOpen 127.0.0.1:$PORT" >>$OBJ/sshd_proxy
 
@@ -31,12 +57,8 @@ start_sshd
 
 # Test Match + PermitOpen in sshd_config. This should be permitted
 for p in 1 2; do
- rm -f $pidfile
         trace "match permitopen localhost proto $p"
- ${SSH} -$p $fwd -F $OBJ/ssh_config -f somehost \
- exec sh -c \'"echo \$\$ > $pidfile; exec sleep 100"\' >>$TEST_SSH_LOGFILE 2>&1 ||\
- fail "match permitopen proto $p sshd failed"
- sleep 1;
+ start_client -F $OBJ/ssh_config
         ${SSH} -q -$p -p $fwdport -F $OBJ/ssh_config somehost true || \
             fail "match permitopen permit proto $p"
         stop_client
@@ -44,12 +66,8 @@ done
 
 # Same but from different source. This should not be permitted
 for p in 1 2; do
- rm -f $pidfile
         trace "match permitopen proxy proto $p"
- ${SSH} -q -$p $fwd -F $OBJ/ssh_proxy -f somehost \
- exec sh -c \'"echo \$\$ > $pidfile; exec sleep 100"\' >>$TEST_SSH_LOGFILE 2>&1 ||\
- fail "match permitopen proxy proto $p sshd failed"
- sleep 1;
+ start_client -F $OBJ/ssh_proxy
         ${SSH} -q -$p -p $fwdport -F $OBJ/ssh_config somehost true && \
             fail "match permitopen deny proto $p"
         stop_client
@@ -61,12 +79,8 @@ cat $OBJ/rsa.pub >> $OBJ/authorized_keys
 echo -n 'permitopen="127.0.0.1:'$PORT'" ' >>$OBJ/authorized_keys_$USER
 cat $OBJ/rsa1.pub >> $OBJ/authorized_keys_$USER
 for p in 1 2; do
- rm -f $pidfile
         trace "match permitopen proxy w/key opts proto $p"
- ${SSH} -q -$p $fwd -F $OBJ/ssh_proxy -f somehost \
- exec sh -c \'"echo \$\$ > $pidfile; exec sleep 100"\' >>$TEST_SSH_LOGFILE 2>&1 ||\
- fail "match permitopen w/key opt proto $p sshd failed"
- sleep 1;
+ start_client -F $OBJ/ssh_proxy
         ${SSH} -q -$p -p $fwdport -F $OBJ/ssh_config somehost true && \
             fail "match permitopen deny w/key opt proto $p"
         stop_client
@@ -75,12 +89,8 @@ done
 # Test both sshd_config and key options permitting the same dst/port pair.
 # Should be permitted.
 for p in 1 2; do
- rm -f $pidfile
         trace "match permitopen localhost proto $p"
- ${SSH} -$p $fwd -F $OBJ/ssh_config -f somehost \
- exec sh -c \'"echo \$\$ > $pidfile; exec sleep 100"\' >>$TEST_SSH_LOGFILE 2>&1 ||\
- fail "match permitopen proto $p sshd failed"
- sleep 1;
+ start_client -F $OBJ/ssh_config
         ${SSH} -q -$p -p $fwdport -F $OBJ/ssh_config somehost true || \
             fail "match permitopen permit proto $p"
         stop_client
@@ -93,12 +103,8 @@ echo "PermitOpen 127.0.0.1:1 127.0.0.1:2
 
 # Test that a Match overrides a PermitOpen in the global section
 for p in 1 2; do
- rm -f $pidfile
         trace "match permitopen proxy w/key opts proto $p"
- ${SSH} -q -$p $fwd -F $OBJ/ssh_proxy -f somehost \
- exec sh -c \'"echo \$\$ > $pidfile; exec sleep 100"\' >>$TEST_SSH_LOGFILE 2>&1 ||\
- fail "match override permitopen proto $p sshd failed"
- sleep 1;
+ start_client -F $OBJ/ssh_proxy
         ${SSH} -q -$p -p $fwdport -F $OBJ/ssh_config somehost true && \
             fail "match override permitopen proto $p"
         stop_client
@@ -112,12 +118,8 @@ echo "PermitOpen 127.0.0.1:1 127.0.0.1:2
 # Test that a rule that doesn't match doesn't override, plus test a
 # PermitOpen entry that's not at the start of the list
 for p in 1 2; do
- rm -f $pidfile
         trace "nomatch permitopen proxy w/key opts proto $p"
- ${SSH} -q -$p $fwd -F $OBJ/ssh_proxy -f somehost \
- exec sh -c \'"echo \$\$ > $pidfile; exec sleep 100"\' >>$TEST_SSH_LOGFILE 2>&1 ||\
- fail "nomatch override permitopen proto $p sshd failed"
- sleep 1;
+ start_client -F $OBJ/ssh_proxy
         ${SSH} -q -$p -p $fwdport -F $OBJ/ssh_config somehost true || \
             fail "nomatch override permitopen proto $p"
         stop_client
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