tpm: Use auth only after NULL check in tpm_buf_check_hmac_response()

Dereference auth after NULL check in tpm_buf_check_hmac_response().
Otherwise, unless tpm2_sessions_init() was called, a call can cause NULL
dereference, when TCG_TPM2_HMAC is enabled.

[jarkko: adjusted the commit message.]
Cc: stable@vger.kernel.org # v6.10+
Fixes: 7ca110f ("tpm: Address !chip->auth in tpm_buf_append_hmac_session*()")
Signed-off-by: Hao Ge <gehao@kylinos.cn>
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>

Author: GeHao01994

drivers/char/tpm/tpm2-sessions.c

@@ -746,15 +746,16 @@ int tpm_buf_check_hmac_response(struct tpm_chip *chip, struct tpm_buf *buf,
 	struct tpm2_auth *auth = chip->auth;
 	off_t offset_s, offset_p;
 	u8 rphash[SHA256_DIGEST_SIZE];
-	u32 attrs;
+	u32 attrs, cc;
 	struct sha256_state sctx;
 	u16 tag = be16_to_cpu(head->tag);
-	u32 cc = be32_to_cpu(auth->ordinal);
 	int parm_len, len, i, handles;
 
 	if (!auth)
 		return rc;
 
+	cc = be32_to_cpu(auth->ordinal);
+
 	if (auth->session >= TPM_HEADER_SIZE) {
 		WARN(1, "tpm session not filled correctly\n");
 		goto out;