tpm: fix checks for policy digest existence in tpm2_seal_trusted()

In my original patch sealing with policy was done with dynamically
allocated buffer that I changed later into an array so the checks in
tpm2-cmd.c became invalid. This patch fixes the issue.

Fixes: 5beb0c435bdd ("keys, trusted: seal with a TPM2 authorization policy")
Reported-by: Dan Carpenter <[e-mail]>
Signed-off-by: Jarkko Sakkinen <[e-mail]>
Acked-by: Peter Huewe <[e-mail]>

drivers/char/tpm/tpm2-cmd.c

···
 	tpm_buf_append_u8(&buf, payload->migratable);
 
 	/* public */
-	if (options->policydigest)
-		tpm_buf_append_u16(&buf, 14 + options->digest_len);
-	else
-		tpm_buf_append_u16(&buf, 14);
-
+	tpm_buf_append_u16(&buf, 14 + options->policydigest_len);
 	tpm_buf_append_u16(&buf, TPM2_ALG_KEYEDHASH);
 	tpm_buf_append_u16(&buf, hash);
 
 	/* policy */
-	if (options->policydigest) {
+	if (options->policydigest_len) {
 		tpm_buf_append_u32(&buf, 0);
-		tpm_buf_append_u16(&buf, options->digest_len);
+		tpm_buf_append_u16(&buf, options->policydigest_len);
 		tpm_buf_append(&buf, options->policydigest,
-			       options->digest_len);
+			       options->policydigest_len);
 	} else {
 		tpm_buf_append_u32(&buf, TPM2_ATTR_USER_WITH_AUTH);
 		tpm_buf_append_u16(&buf, 0);

include/keys/trusted-type.h

···
 	unsigned char pcrinfo[MAX_PCRINFO_SIZE];
 	int pcrlock;
 	uint32_t hash;
-	uint32_t digest_len;
+	uint32_t policydigest_len;
 	unsigned char policydigest[MAX_DIGEST_SIZE];
 	uint32_t policyhandle;
 };

security/keys/trusted.c

···
 	unsigned long handle;
 	unsigned long lock;
 	unsigned long token_mask = 0;
+	unsigned int digest_len;
 	int i;
 	int tpm2;
 
···
 		return tpm2;
 
 	opt->hash = tpm2 ? HASH_ALGO_SHA256 : HASH_ALGO_SHA1;
-	opt->digest_len = hash_digest_size[opt->hash];
 
 	while ((p = strsep(&c, " \t"))) {
 		if (*p == '\0' || *p == ' ' || *p == '\t')
···
 			for (i = 0; i < HASH_ALGO__LAST; i++) {
 				if (!strcmp(args[0].from, hash_algo_name[i])) {
 					opt->hash = i;
-					opt->digest_len =
-						hash_digest_size[opt->hash];
 					break;
 				}
 			}
···
 			}
 			break;
 		case Opt_policydigest:
-			if (!tpm2 ||
-			    strlen(args[0].from) != (2 * opt->digest_len))
+			digest_len = hash_digest_size[opt->hash];
+			if (!tpm2 || strlen(args[0].from) != (2 * digest_len))
 				return -EINVAL;
 			res = hex2bin(opt->policydigest, args[0].from,
-				      opt->digest_len);
+				      digest_len);
 			if (res < 0)
 				return -EINVAL;
+			opt->policydigest_len = digest_len;
 			break;
 		case Opt_policyhandle:
 			if (!tpm2)