On Wed, Sep 02, 2026 at 05:13:40PM +0530, Srish Srinivasan wrote:
> TPM2_Create returns outPrivate, outPublic, creationData, creationHash and
> creationTicket in its response parameter area. However, only outPrivate and
> outPublic are included in the trusted key blob. The size of the blob is
> therefore not determined by the size of the complete response parameter
> area.
>
> tpm2_seal_trusted() currently compares the size of the complete response
> parameter area against MAX_BLOB_SIZE. This can reject a valid response
> when the remaining response outputs cause the entire response parameter
> area to exceed MAX_BLOB_SIZE, even though the outPrivate and outPublic
> TPM2B structures consumed by tpm2_key_encode() remain small enough to be
> encoded in the key blob.
>
> This is observed when creating larger trusted keys using an swtpm TPM 2.0
> emulator backed by libtpms.
>
> For example, requesting a 113-byte key succeeds, 114 fails.
>
> ~$ keyctl add trusted trusted_key1 "new 113 keyhandle=0x81000001" @u
> 520504613
> ~$ keyctl add trusted trusted_key2 "new 114 keyhandle=0x81000001" @u
> add_key: Argument list too long
> ~$
>
> Remove the MAX_BLOB_SIZE check on the complete response parameter area.
> Instead, use the response length passed to tpm2_key_encode() to validate
> that the outPrivate and outPublic TPM2B structures are fully contained
> in the response before accessing them.
>
> Previously, a response parameter area larger than MAX_BLOB_SIZE was
> rejected with -E2BIG before ASN.1 encoding. With this change, if the
> resulting encoded blob does not fit in payload->blob, the error returned by
> asn1_encode_sequence() is propagated instead.
>
> Signed-off-by: Srish Srinivasan <[email protected]>
> ---
> security/keys/trusted-keys/trusted_tpm2.c | 47 +++++++++++++++++++----
> 1 file changed, 39 insertions(+), 8 deletions(-)
>
> diff --git a/security/keys/trusted-keys/trusted_tpm2.c
> b/security/keys/trusted-keys/trusted_tpm2.c
> index 67225dd562a9..efb016a6d4b8 100644
> --- a/security/keys/trusted-keys/trusted_tpm2.c
> +++ b/security/keys/trusted-keys/trusted_tpm2.c
> @@ -24,24 +24,54 @@ static int tpm2_key_encode(struct trusted_key_payload
> *payload,
> u8 *src, u32 len)
> {
> const int SCRATCH_SIZE = PAGE_SIZE;
> - u8 *scratch = kmalloc(SCRATCH_SIZE, GFP_KERNEL);
> - u8 *work = scratch, *work1;
> - u8 *end_work = scratch + SCRATCH_SIZE;
> + u8 *scratch;
> + u8 *work, *work1;
> + u8 *end_work;
> u8 *priv, *pub;
> - u16 priv_len, pub_len;
> + u32 priv_len, pub_len;
> int ret;
>
> - priv_len = get_unaligned_be16(src) + 2;
> + /*
> + * TPM2_Create Response Parameters:
> + *
> + * outPrivate
> + * outPublic
> + * creationData
> + * creationHash
> + * creationTicket
> + *
> + * Validate outPrivate and outPublic against the response parameter
> + * length before accessing them.
> + */
Please remove this comment. It is only an annoyance.
> + if (len < sizeof(__be16))
> + return -EFAULT;
> +
> + priv_len = get_unaligned_be16(src);
> + if (priv_len > len - sizeof(__be16))
> + return -EFAULT;
> +
> + priv_len += sizeof(__be16);
> priv = src;
>
> + if (len - priv_len < sizeof(__be16))
> + return -EFAULT;
> +
> src += priv_len;
>
> - pub_len = get_unaligned_be16(src) + 2;
> + pub_len = get_unaligned_be16(src);
> + if (pub_len > len - priv_len - sizeof(__be16))
> + return -EFAULT;
> +
> + pub_len += sizeof(__be16);
> pub = src;
>
> + scratch = kmalloc(SCRATCH_SIZE, GFP_KERNEL);
> if (!scratch)
> return -ENOMEM;
>
> + work = scratch;
> + end_work = scratch + SCRATCH_SIZE;
> +
> work = asn1_encode_oid(work, end_work, tpm2key_oid,
> asn1_oid_len(tpm2key_oid));
>
> @@ -335,10 +365,11 @@ int tpm2_seal_trusted(struct tpm_chip *chip,
> goto out;
>
> blob_len = tpm_buf_read_u32(buf, &offset);
> - if (blob_len > MAX_BLOB_SIZE || buf->flags & TPM_BUF_INVALID) {
> - rc = -E2BIG;
> + if (buf->flags & TPM_BUF_INVALID) {
> + rc = -EFAULT;
> goto out;
> }
> +
> if (buf->length - offset < blob_len) {
> rc = -EFAULT;
> goto out;
> --
> 2.53.0
>
BR, Jarkko
