Allow empty passwords in sshd when PermitEmptyPasswords is set

.gitignore

@@ -68,6 +68,8 @@ examples/scpclient/wolfscp
 apps/wolfssh/wolfssh
 apps/wolfsshd/wolfsshd
 apps/wolfsshd/test/test_configuration
+apps/wolfsshd/test/log.txt
+apps/wolfsshd/test/sshd_config_*
 
 # test output
 tests/*.test

apps/wolfsshd/auth.c

@@ -363,7 +363,8 @@ static int CheckPasswordUnix(const char* usr, const byte* pw, word32 pwSz, WOLFS
     char* storedHash;
     char* storedHashCpy = NULL;
 
-    if (usr == NULL || pw == NULL) {
+    /* Allow zero length passwords, but not NULL pointers. */
+    if (usr == NULL || (pw == NULL && pwSz != 0)) {
         ret = WS_BAD_ARGUMENT;
     }
 
@@ -373,7 +374,9 @@ static int CheckPasswordUnix(const char* usr, const byte* pw, word32 pwSz, WOLFS
             ret = WS_MEMORY_E;
         }
         else {
-            XMEMCPY(pwStr, pw, pwSz);
+            if (pwSz > 0) {
+                XMEMCPY(pwStr, pw, pwSz);
+            }
             pwStr[pwSz] = 0;
         }
     }

apps/wolfsshd/test/run_all_sshd_tests.sh

@@ -146,9 +146,10 @@ else
     if [ "$USING_LOCAL_HOST" == 1 ]; then
         run_test "sshd_forcedcmd_test.sh"
         run_test "sshd_window_full_test.sh"
+        run_test "sshd_empty_password_test.sh"
     else
         printf "Skipping tests that need to setup local SSHD\n"
-        SKIPPED=$((SKIPPED+2))
+        SKIPPED=$((SKIPPED+3))
     fi
 
     # these tests run with X509 sshd-config loaded

apps/wolfsshd/test/sshd_empty_password_test.sh

@@ -0,0 +1,74 @@
+#!/bin/bash
+
+# Test for empty-password handling.
+
+if [ -z "$1" ] || [ -z "$2" ]; then
+    echo "expecting host and port as arguments"
+    echo "$0 127.0.0.1 22222"
+    exit 1
+fi
+
+TEST_HOST="$1"
+TEST_PORT="$2"
+if [ ! -z "$3" ]; then
+    USER="$3"
+else
+    USER=`whoami`
+fi
+PWD=`pwd`
+
+source ./start_sshd.sh
+
+cat <<EOF > sshd_config_test_emptypw
+Port $TEST_PORT
+Protocol 2
+LoginGraceTime 600
+PermitRootLogin yes
+PasswordAuthentication yes
+PermitEmptyPasswords yes
+UsePrivilegeSeparation no
+UseDNS no
+HostKey $PWD/../../../keys/server-key.pem
+EOF
+
+# Fresh log so we only see this run's output.
+sudo rm -f ./log.txt
+
+start_wolfsshd "sshd_config_test_emptypw"
+if [ -z "$PID" ]; then
+    echo "Failed to start wolfsshd"
+    exit 1
+fi
+
+TEST_CLIENT="../../../examples/client/client"
+
+# Send an empty password
+timeout 10 $TEST_CLIENT -u "$USER" -P "" -c 'true' \
+    -h "$TEST_HOST" -p "$TEST_PORT" > /dev/null 2>&1
+
+# Let wolfsshd flush the log before we stop it.
+sleep 1
+stop_wolfsshd
+
+# log.txt is owned by root (wolfsshd ran via sudo); use sudo to read it.
+if sudo grep -q "No compiled in password check" ./log.txt; then
+    echo "SKIP: wolfsshd built without libcrypt/liblogin support"
+    exit 77
+fi
+
+if sudo grep -q "Error checking password" ./log.txt; then
+    echo "FAIL: empty-password NULL-guard regression detected"
+    echo "----- log.txt -----"
+    sudo cat ./log.txt
+    exit 1
+fi
+
+if ! sudo grep -q "Password incorrect" ./log.txt; then
+    echo "FAIL: empty-password code path was not exercised"
+    echo "(expected '[SSHD] Password incorrect.' in log)"
+    echo "----- log.txt -----"
+    sudo cat ./log.txt
+    exit 1
+fi
+
+exit 0