linux-kernel - Re: [PATCH v3 5/6] tpm: Add tpm_buf_read

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Date:   Fri, 27 Oct 2023 08:24:59 -0400
From:   James Bottomley <James.Bottomley@...senPartnership.com>
To:     Jarkko Sakkinen <jarkko@...nel.org>,
        linux-integrity@...r.kernel.org
Cc:     keyrings@...r.kernel.org,
        William Roberts <bill.c.roberts@...il.com>,
        Stefan Berger <stefanb@...ux.ibm.com>,
        David Howells <dhowells@...hat.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Mimi Zohar <zohar@...ux.ibm.com>,
        Peter Huewe <peterhuewe@....de>,
        Mario Limonciello <mario.limonciello@....com>,
        Julien Gomes <julien@...sta.com>,
        Jerry Snitselaar <jsnitsel@...hat.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 5/6] tpm: Add tpm_buf_read_{u8,u16,u32}

On Tue, 2023-10-24 at 04:15 +0300, Jarkko Sakkinen wrote:
> +++ b/drivers/char/tpm/tpm-buf.c
> @@ -124,3 +124,72 @@ void tpm_buf_append_u32(struct tpm_buf *buf,
> const u32 value)
>         tpm_buf_append(buf, (u8 *)&value2, 4);
>  }
>  EXPORT_SYMBOL_GPL(tpm_buf_append_u32);
> +
> +/**
> + * tpm_buf_read() - Read from a TPM buffer
> + * @buf:       &tpm_buf instance
> + * @offset:    offset within the buffer
> + * @count:     the number of bytes to read
> + * @output:    the output buffer
> + */
> +static void tpm_buf_read(const struct tpm_buf *buf, off_t *offset,
> size_t count, void *output)
> +{
> +       if (*(offset + count) >= buf->length) {

I don't think you mean that; it's dereferencing a random location in
the stack, which is why I see this check trip randomly when testing.  I
think you mean

if (*offset + count >= buf->length) {

James