linux-kernel - [PATCH v3] tpm: Mask TPM RC in tpm2_start_auth

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Message-Id: <20250407072057.81062-1-jarkko@kernel.org>
Date: Mon,  7 Apr 2025 10:20:57 +0300
From: Jarkko Sakkinen <jarkko@...nel.org>
To: keyrings@...r.kernel.org
Cc: Jarkko Sakkinen <jarkko@...nel.org>,
	stable@...r.kernel.org,
	Herbert Xu <herbert@...dor.apana.org.au>,
	David Howells <dhowells@...hat.com>,
	Lukas Wunner <lukas@...ner.de>,
	Ignat Korchagin <ignat@...udflare.com>,
	"David S. Miller" <davem@...emloft.net>,
	Peter Huewe <peterhuewe@....de>,
	Jason Gunthorpe <jgg@...pe.ca>,
	Ard Biesheuvel <ardb@...nel.org>,
	James Bottomley <James.Bottomley@...senPartnership.com>,
	linux-crypto@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-integrity@...r.kernel.org
Subject: [PATCH v3] tpm: Mask TPM RC in tpm2_start_auth_session()

tpm2_start_auth_session() does not mask TPM RC correctly from the callers:

[   28.766528] tpm tpm0: A TPM error (2307) occurred start auth session

Process TPM RCs inside tpm2_start_auth_session(), and map them to POSIX
error codes.

Cc: stable@...r.kernel.org # v6.10+
Fixes: 699e3efd6c64 ("tpm: Add HMAC session start and end functions")
Reported-by: Herbert Xu <herbert@...dor.apana.org.au>
Closes: https://lore.kernel.org/linux-integrity/Z_NgdRHuTKP6JK--@gondor.apana.org.au/
Signed-off-by: Jarkko Sakkinen <jarkko@...nel.org>
---
v3:
- rc > 0
v2:
- Investigate TPM rc only after destroying tpm_buf.
---
 drivers/char/tpm/tpm2-sessions.c | 31 +++++++++++++++++--------------
 include/linux/tpm.h              |  1 +
 2 files changed, 18 insertions(+), 14 deletions(-)

diff --git a/drivers/char/tpm/tpm2-sessions.c b/drivers/char/tpm/tpm2-sessions.c
index 3f89635ba5e8..abd54fb0a45a 100644
--- a/drivers/char/tpm/tpm2-sessions.c
+++ b/drivers/char/tpm/tpm2-sessions.c
@@ -40,11 +40,6 @@
  *
  * These are the usage functions:
  *
- * tpm2_start_auth_session() which allocates the opaque auth structure
- *	and gets a session from the TPM.  This must be called before
- *	any of the following functions.  The session is protected by a
- *	session_key which is derived from a random salt value
- *	encrypted to the NULL seed.
  * tpm2_end_auth_session() kills the session and frees the resources.
  *	Under normal operation this function is done by
  *	tpm_buf_check_hmac_response(), so this is only to be used on
@@ -963,16 +958,13 @@ static int tpm2_load_null(struct tpm_chip *chip, u32 *null_key)
 }
 
 /**
- * tpm2_start_auth_session() - create a HMAC authentication session with the TPM
- * @chip: the TPM chip structure to create the session with
+ * tpm2_start_auth_session() - Create an a HMAC authentication session
+ * @chip:	A TPM chip
  *
- * This function loads the NULL seed from its saved context and starts
- * an authentication session on the null seed, fills in the
- * @chip->auth structure to contain all the session details necessary
- * for performing the HMAC, encrypt and decrypt operations and
- * returns.  The NULL seed is flushed before this function returns.
+ * Loads the ephemeral key (null seed), and starts an HMAC authenticated
+ * session. The null seed is flushed before the return.
  *
- * Return: zero on success or actual error encountered.
+ * Returns zero on success, or a POSIX error code.
  */
 int tpm2_start_auth_session(struct tpm_chip *chip)
 {
@@ -1024,7 +1016,7 @@ int tpm2_start_auth_session(struct tpm_chip *chip)
 	/* hash algorithm for session */
 	tpm_buf_append_u16(&buf, TPM_ALG_SHA256);
 
-	rc = tpm_transmit_cmd(chip, &buf, 0, "start auth session");
+	rc = tpm_transmit_cmd(chip, &buf, 0, "StartAuthSession");
 	tpm2_flush_context(chip, null_key);
 
 	if (rc == TPM2_RC_SUCCESS)
@@ -1032,6 +1024,17 @@ int tpm2_start_auth_session(struct tpm_chip *chip)
 
 	tpm_buf_destroy(&buf);
 
+	if (rc > 0) {
+		switch (rc) {
+		case TPM2_RC_SESSION_MEMORY:
+			rc = -ENOMEM;
+			goto out;
+		default:
+			rc = -EFAULT;
+			goto out;
+		}
+	}
+
 	if (rc == TPM2_RC_SUCCESS) {
 		chip->auth = auth;
 		return 0;
diff --git a/include/linux/tpm.h b/include/linux/tpm.h
index 6c3125300c00..c1d3d60b416f 100644
--- a/include/linux/tpm.h
+++ b/include/linux/tpm.h
@@ -257,6 +257,7 @@ enum tpm2_return_codes {
 	TPM2_RC_TESTING		= 0x090A, /* RC_WARN */
 	TPM2_RC_REFERENCE_H0	= 0x0910,
 	TPM2_RC_RETRY		= 0x0922,
+	TPM2_RC_SESSION_MEMORY	= 0x0903,
 };
 
 enum tpm2_command_codes {
-- 
2.39.5