Address review: TPM publickey auth fallback, reject truncated CA, guard negative CI test, silence maybe-uninitialized

Author: aidangarske

.github/workflows/tpm-ssh.yml

@@ -186,8 +186,14 @@ jobs:
             cat tpmcert_client_neg.txt
             exit 1
         fi
+        echo "----- server -----"; cat tpmcert_server_neg.txt
         echo "client correctly rejected the untrusted server:"
         cat tpmcert_client_neg.txt
+        # Guard against a false pass: the server must have come up, and the
+        # client must have failed inside the SSH handshake (certificate
+        # rejection) rather than from a plain connection failure.
+        grep -q "Listening on port" tpmcert_server_neg.txt
+        grep -q "wolfSSH_connect failed" tpmcert_client_neg.txt
 
     # Client public-key authentication with a TPM-resident key (RSA only).
     - name: Test TPM client public-key auth

examples/tpmcertserver/tpmcertclient.c

@@ -72,14 +72,18 @@ static int TpmCcLoadFile(const char* file, byte* buf, word32* bufSz)
     int ret = 0;
     FILE* f = fopen(file, "rb");
     size_t n;
+    int extra;
 
     if (f == NULL) {
         ret = -1;
     }
     else {
         n = fread(buf, 1, *bufSz, f);
+        /* If the buffer filled exactly, the file may be larger than the buffer;
+         * reject a truncated read rather than loading a partial certificate. */
+        extra = (n == (size_t)*bufSz) ? fgetc(f) : EOF;
         fclose(f);
-        if (n == 0)
+        if (n == 0 || extra != EOF)
             ret = -1;
         else
             *bufSz = (word32)n;

examples/tpmcertserver/tpmcertserver.c

@@ -84,11 +84,11 @@ static int TpmCsMakeKeyAndCert(WOLFTPM2_DEV* dev, WOLFTPM2_KEY* key,
 {
     int rc;
     int devId = INVALID_DEVID;
-    int sigType;
+    int sigType = 0;
     TpmCryptoDevCtx tpmCtx;
     WOLFTPM2_KEY srk;
     TPMT_PUBLIC pub;
-    const char* subject;
+    const char* subject = NULL;
     const char* keyUsage = "serverAuth,clientAuth";
     TPMA_OBJECT attr;
 

src/internal.c

@@ -17688,9 +17688,12 @@ int SendUserAuthRequest(WOLFSSH* ssh, byte authType, int addSig)
 #ifdef WOLFSSH_TPM
         /* When the client has a TPM key configured, prefer publickey auth so
          * the TPM key is used even if the server also offers password or
-         * keyboard-interactive. Applied before any method-specific branch. */
-        if (ssh->ctx->tpmKey != NULL
+         * keyboard-interactive. Only strip the other methods on the first
+         * attempt; once publickey has been tried and rejected, allow fallback
+         * to password/keyboard on the next DoUserAuthFailure() retry. */
+        if (ssh->ctx->tpmKey != NULL && !ssh->tpmPubkeyTried
                 && (authType & WOLFSSH_USERAUTH_PUBLICKEY)) {
+            ssh->tpmPubkeyTried = 1;
             authType &= ~WOLFSSH_USERAUTH_PASSWORD;
         #ifdef WOLFSSH_KEYBOARD_INTERACTIVE
             authType &= ~WOLFSSH_USERAUTH_KEYBOARD;

wolfssh/internal.h

@@ -1033,6 +1033,9 @@ struct WOLFSSH {
     WS_UserAuthData_Keyboard kbAuth;
     byte kbAuthAttempts;
 #endif
+#ifdef WOLFSSH_TPM
+    byte tpmPubkeyTried; /* client tried TPM publickey; allow auth fallback */
+#endif
 #ifdef WOLFSSH_TEST_INTERNAL
     word32 testSftpSendCap;      /* test hook: cap per-call SFTP buffer send */
     word32 testSftpStallPending; /* test hook: force N flush-only resumes */