tpm: Address !chip->auth in tpm_buf_append_hmac_session*()

Unless tpm_chip_bootstrap() was called by the driver, !chip->auth can
cause a null derefence in tpm_buf_hmac_session*().  Thus, address
!chip->auth in tpm_buf_hmac_session*() and remove the fallback
implementation for !TCG_TPM2_HMAC.

Cc: stable@vger.kernel.org # v6.9+
Reported-by: Stefan Berger <stefanb@linux.ibm.com>
Closes: https://lore.kernel.org/linux-integrity/20240617193408.1234365-1-stefanb@linux.ibm.com/
Fixes: 1085b8276b ("tpm: Add the rest of the session HMAC API")
Tested-by: Michael Ellerman <mpe@ellerman.id.au> # ppc
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>

drivers/char/tpm/tpm2-sessions.c

@@ -272,6 +272,110 @@ void tpm_buf_append_name(struct tpm_chip *chip, struct tpm_buf *buf,
 }
 EXPORT_SYMBOL_GPL(tpm_buf_append_name);
 
+/**
+ * tpm_buf_append_hmac_session() - Append a TPM session element
+ * @chip: the TPM chip structure
+ * @buf: The buffer to be appended
+ * @attributes: The session attributes
+ * @passphrase: The session authority (NULL if none)
+ * @passphrase_len: The length of the session authority (0 if none)
+ *
+ * This fills in a session structure in the TPM command buffer, except
+ * for the HMAC which cannot be computed until the command buffer is
+ * complete.  The type of session is controlled by the @attributes,
+ * the main ones of which are TPM2_SA_CONTINUE_SESSION which means the
+ * session won't terminate after tpm_buf_check_hmac_response(),
+ * TPM2_SA_DECRYPT which means this buffers first parameter should be
+ * encrypted with a session key and TPM2_SA_ENCRYPT, which means the
+ * response buffer's first parameter needs to be decrypted (confusing,
+ * but the defines are written from the point of view of the TPM).
+ *
+ * Any session appended by this command must be finalized by calling
+ * tpm_buf_fill_hmac_session() otherwise the HMAC will be incorrect
+ * and the TPM will reject the command.
+ *
+ * As with most tpm_buf operations, success is assumed because failure
+ * will be caused by an incorrect programming model and indicated by a
+ * kernel message.
+ */
+void tpm_buf_append_hmac_session(struct tpm_chip *chip, struct tpm_buf *buf,
+				 u8 attributes, u8 *passphrase,
+				 int passphrase_len)
+{
+#ifdef CONFIG_TCG_TPM2_HMAC
+	u8 nonce[SHA256_DIGEST_SIZE];
+	struct tpm2_auth *auth;
+	u32 len;
+#endif
+
+	if (!tpm2_chip_auth(chip)) {
+		/* offset tells us where the sessions area begins */
+		int offset = buf->handles * 4 + TPM_HEADER_SIZE;
+		u32 len = 9 + passphrase_len;
+
+		if (tpm_buf_length(buf) != offset) {
+			/* not the first session so update the existing length */
+			len += get_unaligned_be32(&buf->data[offset]);
+			put_unaligned_be32(len, &buf->data[offset]);
+		} else {
+			tpm_buf_append_u32(buf, len);
+		}
+		/* auth handle */
+		tpm_buf_append_u32(buf, TPM2_RS_PW);
+		/* nonce */
+		tpm_buf_append_u16(buf, 0);
+		/* attributes */
+		tpm_buf_append_u8(buf, 0);
+		/* passphrase */
+		tpm_buf_append_u16(buf, passphrase_len);
+		tpm_buf_append(buf, passphrase, passphrase_len);
+		return;
+	}
+
+#ifdef CONFIG_TCG_TPM2_HMAC
+	/*
+	 * The Architecture Guide requires us to strip trailing zeros
+	 * before computing the HMAC
+	 */
+	while (passphrase && passphrase_len > 0 && passphrase[passphrase_len - 1] == '\0')
+		passphrase_len--;
+
+	auth = chip->auth;
+	auth->attrs = attributes;
+	auth->passphrase_len = passphrase_len;
+	if (passphrase_len)
+		memcpy(auth->passphrase, passphrase, passphrase_len);
+
+	if (auth->session != tpm_buf_length(buf)) {
+		/* we're not the first session */
+		len = get_unaligned_be32(&buf->data[auth->session]);
+		if (4 + len + auth->session != tpm_buf_length(buf)) {
+			WARN(1, "session length mismatch, cannot append");
+			return;
+		}
+
+		/* add our new session */
+		len += 9 + 2 * SHA256_DIGEST_SIZE;
+		put_unaligned_be32(len, &buf->data[auth->session]);
+	} else {
+		tpm_buf_append_u32(buf, 9 + 2 * SHA256_DIGEST_SIZE);
+	}
+
+	/* random number for our nonce */
+	get_random_bytes(nonce, sizeof(nonce));
+	memcpy(auth->our_nonce, nonce, sizeof(nonce));
+	tpm_buf_append_u32(buf, auth->handle);
+	/* our new nonce */
+	tpm_buf_append_u16(buf, SHA256_DIGEST_SIZE);
+	tpm_buf_append(buf, nonce, SHA256_DIGEST_SIZE);
+	tpm_buf_append_u8(buf, auth->attrs);
+	/* and put a placeholder for the hmac */
+	tpm_buf_append_u16(buf, SHA256_DIGEST_SIZE);
+	tpm_buf_append(buf, nonce, SHA256_DIGEST_SIZE);
+#endif
+}
+EXPORT_SYMBOL_GPL(tpm_buf_append_hmac_session);
+
 #ifdef CONFIG_TCG_TPM2_HMAC
 
 static int tpm2_create_primary(struct tpm_chip *chip, u32 hierarchy,
@@ -457,82 +561,6 @@ static void tpm_buf_append_salt(struct tpm_buf *buf, struct tpm_chip *chip)
 	crypto_free_kpp(kpp);
 }
 
-/**
- * tpm_buf_append_hmac_session() - Append a TPM session element
- * @chip: the TPM chip structure
- * @buf: The buffer to be appended
- * @attributes: The session attributes
- * @passphrase: The session authority (NULL if none)
- * @passphrase_len: The length of the session authority (0 if none)
- *
- * This fills in a session structure in the TPM command buffer, except
- * for the HMAC which cannot be computed until the command buffer is
- * complete.  The type of session is controlled by the @attributes,
- * the main ones of which are TPM2_SA_CONTINUE_SESSION which means the
- * session won't terminate after tpm_buf_check_hmac_response(),
- * TPM2_SA_DECRYPT which means this buffers first parameter should be
- * encrypted with a session key and TPM2_SA_ENCRYPT, which means the
- * response buffer's first parameter needs to be decrypted (confusing,
- * but the defines are written from the point of view of the TPM).
- *
- * Any session appended by this command must be finalized by calling
- * tpm_buf_fill_hmac_session() otherwise the HMAC will be incorrect
- * and the TPM will reject the command.
- *
- * As with most tpm_buf operations, success is assumed because failure
- * will be caused by an incorrect programming model and indicated by a
- * kernel message.
- */
-void tpm_buf_append_hmac_session(struct tpm_chip *chip, struct tpm_buf *buf,
-				 u8 attributes, u8 *passphrase,
-				 int passphrase_len)
-{
-	u8 nonce[SHA256_DIGEST_SIZE];
-	u32 len;
-	struct tpm2_auth *auth = chip->auth;
-
-	/*
-	 * The Architecture Guide requires us to strip trailing zeros
-	 * before computing the HMAC
-	 */
-	while (passphrase && passphrase_len > 0
-	       && passphrase[passphrase_len - 1] == '\0')
-		passphrase_len--;
-
-	auth->attrs = attributes;
-	auth->passphrase_len = passphrase_len;
-	if (passphrase_len)
-		memcpy(auth->passphrase, passphrase, passphrase_len);
-
-	if (auth->session != tpm_buf_length(buf)) {
-		/* we're not the first session */
-		len = get_unaligned_be32(&buf->data[auth->session]);
-		if (4 + len + auth->session != tpm_buf_length(buf)) {
-			WARN(1, "session length mismatch, cannot append");
-			return;
-		}
-
-		/* add our new session */
-		len += 9 + 2 * SHA256_DIGEST_SIZE;
-		put_unaligned_be32(len, &buf->data[auth->session]);
-	} else {
-		tpm_buf_append_u32(buf, 9 + 2 * SHA256_DIGEST_SIZE);
-	}
-
-	/* random number for our nonce */
-	get_random_bytes(nonce, sizeof(nonce));
-	memcpy(auth->our_nonce, nonce, sizeof(nonce));
-	tpm_buf_append_u32(buf, auth->handle);
-	/* our new nonce */
-	tpm_buf_append_u16(buf, SHA256_DIGEST_SIZE);
-	tpm_buf_append(buf, nonce, SHA256_DIGEST_SIZE);
-	tpm_buf_append_u8(buf, auth->attrs);
-	/* and put a placeholder for the hmac */
-	tpm_buf_append_u16(buf, SHA256_DIGEST_SIZE);
-	tpm_buf_append(buf, nonce, SHA256_DIGEST_SIZE);
-}
-EXPORT_SYMBOL(tpm_buf_append_hmac_session);
-
 /**
  * tpm_buf_fill_hmac_session() - finalize the session HMAC
  * @chip: the TPM chip structure
@@ -563,6 +591,9 @@ void tpm_buf_fill_hmac_session(struct tpm_chip *chip, struct tpm_buf *buf)
 	u8 cphash[SHA256_DIGEST_SIZE];
 	struct sha256_state sctx;
 
+	if (!auth)
+		return;
+
 	/* save the command code in BE format */
 	auth->ordinal = head->ordinal;
 
@@ -721,6 +752,9 @@ int tpm_buf_check_hmac_response(struct tpm_chip *chip, struct tpm_buf *buf,
 	u32 cc = be32_to_cpu(auth->ordinal);
 	int parm_len, len, i, handles;
 
+	if (!auth)
+		return rc;
+
 	if (auth->session >= TPM_HEADER_SIZE) {
 		WARN(1, "tpm session not filled correctly\n");
 		goto out;

include/linux/tpm.h

@@ -502,10 +502,6 @@ static inline struct tpm2_auth *tpm2_chip_auth(struct tpm_chip *chip)
 
 void tpm_buf_append_name(struct tpm_chip *chip, struct tpm_buf *buf,
 			 u32 handle, u8 *name);
-
-#ifdef CONFIG_TCG_TPM2_HMAC
-
-int tpm2_start_auth_session(struct tpm_chip *chip);
 void tpm_buf_append_hmac_session(struct tpm_chip *chip, struct tpm_buf *buf,
 				 u8 attributes, u8 *passphrase,
 				 int passphraselen);
@@ -515,9 +511,27 @@ static inline void tpm_buf_append_hmac_session_opt(struct tpm_chip *chip,
 						   u8 *passphrase,
 						   int passphraselen)
 {
-	tpm_buf_append_hmac_session(chip, buf, attributes, passphrase,
+	struct tpm_header *head;
-				    passphraselen);
+	int offset;
+
+	if (tpm2_chip_auth(chip)) {
+		tpm_buf_append_hmac_session(chip, buf, attributes, passphrase, passphraselen);
+	} else  {
+		offset = buf->handles * 4 + TPM_HEADER_SIZE;
+		head = (struct tpm_header *)buf->data;
+
+		/*
+		 * If the only sessions are optional, the command tag must change to
+		 * TPM2_ST_NO_SESSIONS.
+		 */
+		if (tpm_buf_length(buf) == offset)
+			head->tag = cpu_to_be16(TPM2_ST_NO_SESSIONS);
+	}
 }
+
+#ifdef CONFIG_TCG_TPM2_HMAC
+
+int tpm2_start_auth_session(struct tpm_chip *chip);
 void tpm_buf_fill_hmac_session(struct tpm_chip *chip, struct tpm_buf *buf);
 int tpm_buf_check_hmac_response(struct tpm_chip *chip, struct tpm_buf *buf,
 				int rc);
@@ -532,48 +546,6 @@ static inline int tpm2_start_auth_session(struct tpm_chip *chip)
 static inline void tpm2_end_auth_session(struct tpm_chip *chip)
 {
 }
-static inline void tpm_buf_append_hmac_session(struct tpm_chip *chip,
-					       struct tpm_buf *buf,
-					       u8 attributes, u8 *passphrase,
-					       int passphraselen)
-{
-	/* offset tells us where the sessions area begins */
-	int offset = buf->handles * 4 + TPM_HEADER_SIZE;
-	u32 len = 9 + passphraselen;
-
-	if (tpm_buf_length(buf) != offset) {
-		/* not the first session so update the existing length */
-		len += get_unaligned_be32(&buf->data[offset]);
-		put_unaligned_be32(len, &buf->data[offset]);
-	} else {
-		tpm_buf_append_u32(buf, len);
-	}
-	/* auth handle */
-	tpm_buf_append_u32(buf, TPM2_RS_PW);
-	/* nonce */
-	tpm_buf_append_u16(buf, 0);
-	/* attributes */
-	tpm_buf_append_u8(buf, 0);
-	/* passphrase */
-	tpm_buf_append_u16(buf, passphraselen);
-	tpm_buf_append(buf, passphrase, passphraselen);
-}
-static inline void tpm_buf_append_hmac_session_opt(struct tpm_chip *chip,
-						   struct tpm_buf *buf,
-						   u8 attributes,
-						   u8 *passphrase,
-						   int passphraselen)
-{
-	int offset = buf->handles * 4 + TPM_HEADER_SIZE;
-	struct tpm_header *head = (struct tpm_header *) buf->data;
-
-	/*
-	 * if the only sessions are optional, the command tag
-	 * must change to TPM2_ST_NO_SESSIONS
-	 */
-	if (tpm_buf_length(buf) == offset)
-		head->tag = cpu_to_be16(TPM2_ST_NO_SESSIONS);
-}
 static inline void tpm_buf_fill_hmac_session(struct tpm_chip *chip,
 					     struct tpm_buf *buf)
 {