linux-kernel - Re: [PATCH] tpm: Wrap the buffer from the caller to tpm_buf in tpm

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Date:   Mon, 16 Sep 2019 14:03:31 -0700
From:   Jerry Snitselaar <jsnitsel@...hat.com>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Cc:     linux-integrity@...r.kernel.org, Mimi Zohar <zohar@...ux.ibm.com>,
        stable@...r.kernel.org, Peter Huewe <peterhuewe@....de>,
        Jason Gunthorpe <jgg@...pe.ca>, Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tpm: Wrap the buffer from the caller to tpm_buf in
 tpm_send()

On Mon Sep 16 19, Jarkko Sakkinen wrote:
>tpm_send() does not give anymore the result back to the caller. This
>would require another memcpy(), which kind of tells that the whole
>approach is somewhat broken. Instead, as Mimi suggested, this commit
>just wraps the data to the tpm_buf, and thus the result will not go to
>the garbage.
>
>Obviously this assumes from the caller that it passes large enough
>buffer, which makes the whole API somewhat broken because it could be
>different size than @buflen but since trusted keys is the only module
>using this API right now I think that this fix is sufficient for the
>moment.
>
>In the near future the plan is to replace the parameters with a tpm_buf
>created by the caller.
>
>Reported-by: Mimi Zohar <zohar@...ux.ibm.com>
>Suggested-by: Mimi Zohar <zohar@...ux.ibm.com>
>Cc: stable@...r.kernel.org
>Fixes: 412eb585587a ("use tpm_buf in tpm_transmit_cmd() as the IO parameter")
>Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
>---
> drivers/char/tpm/tpm-interface.c | 8 ++------
> 1 file changed, 2 insertions(+), 6 deletions(-)
>
>diff --git a/drivers/char/tpm/tpm-interface.c b/drivers/char/tpm/tpm-interface.c
>index d9ace5480665..2459d36dd8cc 100644
>--- a/drivers/char/tpm/tpm-interface.c
>+++ b/drivers/char/tpm/tpm-interface.c
>@@ -358,13 +358,9 @@ int tpm_send(struct tpm_chip *chip, void *cmd, size_t buflen)
> 	if (!chip)
> 		return -ENODEV;
>
>-	rc = tpm_buf_init(&buf, 0, 0);
>-	if (rc)
>-		goto out;
>-
>-	memcpy(buf.data, cmd, buflen);
>+	buf.data = cmd;
> 	rc = tpm_transmit_cmd(chip, &buf, 0, "attempting to a send a command");
>-	tpm_buf_destroy(&buf);
>+
> out:
> 	tpm_put_ops(chip);
> 	return rc;
>-- 
>2.20.1
>

Nothing uses the out label any longer so it should be dropped as well, but other than that...

Acked-by: Jerry Snitselaar <jsnitsel@...hat.com>