tpm: Cap the number of PCR banks

tpm2_get_pcr_allocation() does not cap any upper limit for the number of
banks. Cap the limit to eight banks so that out of bounds values coming
from external I/O cause on only limited harm.

Cc: [e-mail] # v5.10+
Fixes: bcfff8384f6c ("tpm: dynamically allocate the allocated_banks array")
Tested-by: Lai Yi <[e-mail]>
Reviewed-by: Jonathan McDowell <[e-mail]>
Reviewed-by: Roberto Sassu <[e-mail]>
Signed-off-by: Jarkko Sakkinen <[e-mail]>

drivers/char/tpm/tpm-chip.c

···
 
 	kfree(chip->work_space.context_buf);
 	kfree(chip->work_space.session_buf);
-	kfree(chip->allocated_banks);
 #ifdef CONFIG_TCG_TPM2_HMAC
 	kfree(chip->auth);
 #endif

drivers/char/tpm/tpm1-cmd.c

···
  */
 int tpm1_get_pcr_allocation(struct tpm_chip *chip)
 {
-	chip->allocated_banks = kcalloc(1, sizeof(*chip->allocated_banks),
-					GFP_KERNEL);
-	if (!chip->allocated_banks)
-		return -ENOMEM;
-
 	chip->allocated_banks[0].alg_id = TPM_ALG_SHA1;
 	chip->allocated_banks[0].digest_size = hash_digest_size[HASH_ALGO_SHA1];
 	chip->allocated_banks[0].crypto_id = HASH_ALGO_SHA1;

drivers/char/tpm/tpm2-cmd.c

···
 
 	nr_possible_banks = be32_to_cpup(
 		(__be32 *)&buf.data[TPM_HEADER_SIZE + 5]);
-
-	chip->allocated_banks = kcalloc(nr_possible_banks,
-					sizeof(*chip->allocated_banks),
-					GFP_KERNEL);
-	if (!chip->allocated_banks) {
+	if (nr_possible_banks > TPM2_MAX_PCR_BANKS) {
+		pr_err("tpm: out of bank capacity: %u > %u\n",
+		       nr_possible_banks, TPM2_MAX_PCR_BANKS);
 		rc = -ENOMEM;
 		goto out;
 	}

include/linux/tpm.h

···
 #include <crypto/aes.h>
 
 #define TPM_DIGEST_SIZE 20	/* Max TPM v1.2 PCR size */
-#define TPM_MAX_DIGEST_SIZE SHA512_DIGEST_SIZE
+
+#define TPM2_MAX_DIGEST_SIZE	SHA512_DIGEST_SIZE
+#define TPM2_MAX_PCR_BANKS	8
 
 struct tpm_chip;
 struct trusted_key_payload;
···
 
 struct tpm_digest {
 	u16 alg_id;
-	u8 digest[TPM_MAX_DIGEST_SIZE];
+	u8 digest[TPM2_MAX_DIGEST_SIZE];
 } __packed;
 
 struct tpm_bank_info {
···
 	unsigned int groups_cnt;
 
 	u32 nr_allocated_banks;
-	struct tpm_bank_info *allocated_banks;
+	struct tpm_bank_info allocated_banks[TPM2_MAX_PCR_BANKS];
 #ifdef CONFIG_ACPI
 	acpi_handle acpi_dev_handle;
 	char ppi_version[TPM_PPI_VERSION_LEN + 1];