Re: [PATCH v3 2/4] tpm2-sessions: Fix tpm2_read_public range checks

[Jarkko Sakkinen <jarkko@kernel.org>]

On Thu, Dec 04, 2025 at 03:20:26PM +0000, Jonathan McDowell wrote:
> On Thu, Dec 04, 2025 at 12:12:12AM +0200, Jarkko Sakkinen wrote:
> > 'tpm2_read_public' has some rudimentary range checks but the function
> > does not ensure that the response buffer has enough bytes for the full
> > TPMT_HA payload.
> > 
> > Re-implement the function with necessary checks and validation.
> > 
> > Cc: stable@vger.kernel.org # v6.10+
> > Fixes: d0a25bb961e6 ("tpm: Add HMAC session name/handle append")
> > Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
> 
> A minor nit about variable naming, but:
> 
> Reviewed-by: Jonathan McDowell <noodles@meta.com>
> 
> > v2:
> > - Made the fix localized instead of spread all over the place.
> > ---
> > drivers/char/tpm/tpm2-cmd.c      |  3 ++
> > drivers/char/tpm/tpm2-sessions.c | 77 +++++++++++++++++---------------
> > 2 files changed, 44 insertions(+), 36 deletions(-)
> > 
> > diff --git a/drivers/char/tpm/tpm2-cmd.c b/drivers/char/tpm/tpm2-cmd.c
> > index be4a9c7f2e1a..34e3599f094f 100644
> > --- a/drivers/char/tpm/tpm2-cmd.c
> > +++ b/drivers/char/tpm/tpm2-cmd.c
> > @@ -11,8 +11,11 @@
> >  * used by the kernel internally.
> >  */
> > 
> > +#include "linux/dev_printk.h"
> > +#include "linux/tpm.h"
> > #include "tpm.h"
> > #include <crypto/hash_info.h>
> > +#include <linux/unaligned.h>
> > 
> > static bool disable_pcr_integrity;
> > module_param(disable_pcr_integrity, bool, 0444);
> > diff --git a/drivers/char/tpm/tpm2-sessions.c b/drivers/char/tpm/tpm2-sessions.c
> > index a265e9752a5e..e9f439be3916 100644
> > --- a/drivers/char/tpm/tpm2-sessions.c
> > +++ b/drivers/char/tpm/tpm2-sessions.c
> > @@ -163,54 +163,59 @@ static int name_size(const u8 *name)
> > 	}
> > }
> > 
> > -static int tpm2_parse_read_public(char *name, struct tpm_buf *buf)
> > +static int tpm2_read_public(struct tpm_chip *chip, u32 handle, void *name)
> > {
> > -	struct tpm_header *head = (struct tpm_header *)buf->data;
> > +	u32 mso = tpm2_handle_mso(handle);
> > 	off_t offset = TPM_HEADER_SIZE;
> > -	u32 tot_len = be32_to_cpu(head->length);
> > -	int ret;
> > -	u32 val;
> > -
> > -	/* we're starting after the header so adjust the length */
> > -	tot_len -= TPM_HEADER_SIZE;
> > -
> > -	/* skip public */
> > -	val = tpm_buf_read_u16(buf, &offset);
> > -	if (val > tot_len)
> > -		return -EINVAL;
> > -	offset += val;
> > -	/* name */
> > -
> > -	val = tpm_buf_read_u16(buf, &offset);
> > -	ret = name_size(&buf->data[offset]);
> > -	if (ret < 0)
> > -		return ret;
> > +	struct tpm_buf buf;
> > +	int rc, rc2;
> > 
> > -	if (val != ret)
> > +	if (mso != TPM2_MSO_PERSISTENT && mso != TPM2_MSO_VOLATILE &&
> > +	    mso != TPM2_MSO_NVRAM)
> > 		return -EINVAL;
> > 
> > -	memcpy(name, &buf->data[offset], val);
> > -	/* forget the rest */
> > -	return 0;
> > -}
> > -
> > -static int tpm2_read_public(struct tpm_chip *chip, u32 handle, char *name)
> > -{
> > -	struct tpm_buf buf;
> > -	int rc;
> > -
> > 	rc = tpm_buf_init(&buf, TPM2_ST_NO_SESSIONS, TPM2_CC_READ_PUBLIC);
> > 	if (rc)
> > 		return rc;
> > 
> > 	tpm_buf_append_u32(&buf, handle);
> > -	rc = tpm_transmit_cmd(chip, &buf, 0, "read public");
> > -	if (rc == TPM2_RC_SUCCESS)
> > -		rc = tpm2_parse_read_public(name, &buf);
> > 
> > -	tpm_buf_destroy(&buf);
> > +	rc = tpm_transmit_cmd(chip, &buf, 0, "TPM2_ReadPublic");
> > +	if (rc) {
> > +		tpm_buf_destroy(&buf);
> > +		return tpm_ret_to_err(rc);
> > +	}
> > 
> > -	return rc;
> > +	/* Skip TPMT_PUBLIC: */
> > +	offset += tpm_buf_read_u16(&buf, &offset);
> > +
> > +	/*
> > +	 * Ensure space for the length field of TPM2B_NAME and hashAlg field of
> > +	 * TPMT_HA (the extra four bytes).
> > +	 */
> > +	if (offset + 4 > tpm_buf_length(&buf)) {
> > +		tpm_buf_destroy(&buf);
> > +		return -EIO;
> > +	}
> > +
> > +	rc = tpm_buf_read_u16(&buf, &offset);
> > +	rc2 = name_size(&buf.data[offset]);
> 
> rc2 is not great naming. We only use it for this, so perhaps name_len?

I'll rename it as 'name_size_alg' for the sake of clarity. It is TPM
name size mapped from algorithm ID. That should make the means and
purpose dead obvious.

BR, Jarkko