Re: [PATCH v5 8/8] KEYS: trusted: tpm2: Use struct tpm_buf for sized buffers

Jarkko Sakkinen
2023-12-04T04:03:15Z

On Tue Nov 28, 2023 at 5:48 AM EET, Serge E. Hallyn wrote:
> On Wed, Nov 22, 2023 at 12:31:20AM +0200, Jarkko Sakkinen wrote:
> > Take advantage of the new sized buffer (TPM2B) mode of struct tpm_buf in
> > tpm2_seal_trusted(). This allows to add robustness to the command
> > construction without requiring to calculate buffer sizes manually.
> >
> > Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
> > ---
> > v3 [2023-11-21]: A boundary error check as response for the feeedback
> > from Mario Limenciello:
> > https://lore.kernel.org/linux-integrity/3f9086f6-935f-48a7-889b-c71398422fa1@amd.com/
> > v2: Use tpm_buf_read_*
> > ---
> > security/keys/trusted-keys/trusted_tpm2.c | 54 +++++++++++++----------
> > 1 file changed, 31 insertions(+), 23 deletions(-)
> >
> > diff --git a/security/keys/trusted-keys/trusted_tpm2.c b/security/keys/trusted-keys/trusted_tpm2.c
> > index bc700f85f80b..97b1dfca2dba 100644
> > --- a/security/keys/trusted-keys/trusted_tpm2.c
> > +++ b/security/keys/trusted-keys/trusted_tpm2.c
> > @@ -228,8 +228,9 @@ int tpm2_seal_trusted(struct tpm_chip *chip,
> > struct trusted_key_payload *payload,
> > struct trusted_key_options *options)
> > {
> > + off_t offset = TPM_HEADER_SIZE;
> > + struct tpm_buf buf, sized;
> > int blob_len = 0;
> > - struct tpm_buf buf;
> > u32 hash;
> > u32 flags;
> > int i;
> > @@ -258,6 +259,14 @@ int tpm2_seal_trusted(struct tpm_chip *chip,
> > return rc;
> > }
> >
> > + rc = tpm_buf_init_sized(&sized);
> > + if (rc) {
> > + tpm_buf_destroy(&buf);
>
> It won't really hurt, but at the moment if tpm_buf_init_sized() returns
> non-zero, then it must be returning -ENOMEM, and tpm_buf_destroy(&buf)
> is not needed, right?

It should cause corrateral damage since the rollback emits only
free_page(buf->data) and it will become NULL in the case when
tpm_buf_init_sized(). Despite that this behaviour is illegit and
the call should be removed. Thanks for the remark!

BR, Jarkko