[PATCH 3.16 026/136] tpm-dev-common: Reject too short writes

[Ben Hutchings]

3.16.54-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Alexander Steffen <Alexander.Steffen@xxxxxxxxxxxx>

commit ee70bc1e7b63ac8023c9ff9475d8741e397316e7 upstream.

tpm_transmit() does not offer an explicit interface to indicate the number
of valid bytes in the communication buffer. Instead, it relies on the
commandSize field in the TPM header that is encoded within the buffer.
Therefore, ensure that a) enough data has been written to the buffer, so
that the commandSize field is present and b) the commandSize field does not
announce more data than has been written to the buffer.

This should have been fixed with CVE-2011-1161 long ago, but apparently
a correct version of that patch never made it into the kernel.

Signed-off-by: Alexander Steffen <Alexander.Steffen@xxxxxxxxxxxx>
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@xxxxxxxxxxxxxxx>
Tested-by: Jarkko Sakkinen <jarkko.sakkinen@xxxxxxxxxxxxxxx>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@xxxxxxxxxxxxxxx>
[bwh: Backported to 3.16: adjust filename, context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 drivers/char/tpm/tpm-dev.c | 6 ++++++
 1 file changed, 6 insertions(+)

--- a/drivers/char/tpm/tpm-dev.c
+++ b/drivers/char/tpm/tpm-dev.c
@@ -139,6 +139,12 @@ static ssize_t tpm_write(struct file *fi
 		return -EFAULT;
 	}
 
+	if (in_size < 6 ||
+	    in_size < be32_to_cpu(*((__be32 *) (priv->data_buffer + 2)))) {
+		mutex_unlock(&priv->buffer_mutex);
+		return -EINVAL;
+	}
+
 	/* atomic tpm command send and result receive */
 	out_size = tpm_transmit(priv->chip, priv->data_buffer,
 				sizeof(priv->data_buffer));