Re: [PATCH v6] tpm: Check size of response before accessing data

[Stefan Berger]

On 01/17/2017 09:49 AM, Jarkko Sakkinen wrote:
On Mon, Jan 16, 2017 at 04:41:11PM -0500, Stefan Berger wrote:
+ * @min_rx_length: minimum expected length of response
Please, rename as min_rsp_body_len and change the description
accordingly.

   * @flags: tpm transmit flags - bitmap
   * @desc: command description used in the error message
   *
@@ -434,25 +435,34 @@ ssize_t tpm_transmit(struct tpm_chip *chip, const u8 
*buf, size_t bufsiz,
   *     A positive number for a TPM error.
   */
  ssize_t tpm_transmit_cmd(struct tpm_chip *chip, const void *cmd,
-                        int len, unsigned int flags, const char *desc)
+                        size_t cmd_length, size_t min_rx_length,
+                        unsigned int flags, const char *desc)
  {
        const struct tpm_output_header *header;
        int err;
+       ssize_t len;
  
-	len = tpm_transmit(chip, (const u8 *)cmd, len, flags);
+       len = tpm_transmit(chip, (const u8 *)cmd, cmd_length, flags);
        if (len <  0)
                return len;
        else if (len < TPM_HEADER_SIZE)
                return -EFAULT;
  
  	header = cmd;
+       if (len < be32_to_cpu(header->length))
+               return -EFAULT;
  
  	err = be32_to_cpu(header->return_code);
        if (err != 0 && desc)
                dev_err(&chip->dev, "A TPM error (%d) occurred %s\n", err,
                        desc);
+       if (err)
+               return err;
  
-	return err;
+       if (be32_to_cpu(header->length) < min_rx_length)
+               return -EFAULT;
+
+       return 0;
  }
  
  #define TPM_DIGEST_SIZE 20
@@ -468,7 +478,7 @@ static const struct tpm_input_header tpm_getcap_header = {
  };
  
  ssize_t tpm_getcap(struct tpm_chip *chip, u32 subcap_id, cap_t *cap,
-                  const char *desc)
+                  const char *desc, size_t min_cap_length)
tpm_getcap update should be its own commit.

tpm_getcap needs to pass something as min_rsp_body_length to 
tpm_transmit_cmd. What would it pass?