Re: [PATCH] tpm: fix a race condition tpm2_unseal_trusted()
From: Jarkko Sakkinen
Date: Wed Aug 17 2016 - 00:31:27 EST
On Tue, Aug 16, 2016 at 10:38:22PM +0300, Jarkko Sakkinen wrote:
> Unseal and load operations should be done as an atomic operation. This
> commit introduces unlocked tpm_transmit() so that tpm2_unseal_trusted()
> can do the locking by itself.
>
> v2: Introduced an unlocked unseal operation instead of changing locking
> strategy in order to make less intrusive bug fix and thus more
> backportable.
>
> CC: stable@xxxxxxxxxxxxxxx
> Fixes: 954650efb79f ("tpm: seal/unseal for TPM 2.0")
> Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@xxxxxxxxxxxxxxx>
> ---
> drivers/char/tpm/tpm-dev.c | 2 +-
> drivers/char/tpm/tpm-interface.c | 14 ++++++++------
> drivers/char/tpm/tpm.h | 18 ++++++++++++++----
> drivers/char/tpm/tpm2-cmd.c | 13 +++++++++----
> 4 files changed, 32 insertions(+), 15 deletions(-)
>
> diff --git a/drivers/char/tpm/tpm-dev.c b/drivers/char/tpm/tpm-dev.c
> index f5d4521..8df8846 100644
> --- a/drivers/char/tpm/tpm-dev.c
> +++ b/drivers/char/tpm/tpm-dev.c
> @@ -145,7 +145,7 @@ static ssize_t tpm_write(struct file *file, const char __user *buf,
> return -EPIPE;
> }
> out_size = tpm_transmit(priv->chip, priv->data_buffer,
> - sizeof(priv->data_buffer));
> + sizeof(priv->data_buffer), TPM_TRANSMIT_LOCK);
>
> tpm_put_ops(priv->chip);
> if (out_size < 0) {
> diff --git a/drivers/char/tpm/tpm-interface.c b/drivers/char/tpm/tpm-interface.c
> index 43ef0ef..627daa7 100644
> --- a/drivers/char/tpm/tpm-interface.c
> +++ b/drivers/char/tpm/tpm-interface.c
> @@ -331,7 +331,7 @@ EXPORT_SYMBOL_GPL(tpm_calc_ordinal_duration);
> * Internal kernel interface to transmit TPM commands
> */
> ssize_t tpm_transmit(struct tpm_chip *chip, const char *buf,
> - size_t bufsiz)
> + size_t bufsiz, unsigned int flags)
> {
> ssize_t rc;
> u32 count, ordinal;
> @@ -350,7 +350,8 @@ ssize_t tpm_transmit(struct tpm_chip *chip, const char *buf,
> return -E2BIG;
> }
>
> - mutex_lock(&chip->tpm_mutex);
> + if (flags & TPM_TRANSMIT_LOCK)
> + mutex_lock(&chip->tpm_mutex);
>
> rc = chip->ops->send(chip, (u8 *) buf, count);
> if (rc < 0) {
> @@ -393,20 +394,21 @@ out_recv:
> dev_err(&chip->dev,
> "tpm_transmit: tpm_recv: error %zd\n", rc);
> out:
> - mutex_unlock(&chip->tpm_mutex);
> + if (flags & TPM_TRANSMIT_LOCK)
> + mutex_unlock(&chip->tpm_mutex);
> return rc;
> }
>
> #define TPM_DIGEST_SIZE 20
> #define TPM_RET_CODE_IDX 6
>
> -ssize_t tpm_transmit_cmd(struct tpm_chip *chip, void *cmd,
> - int len, const char *desc)
> +ssize_t __tpm_transmit_cmd(struct tpm_chip *chip, void *cmd,
> + int len, const char *desc, unsigned int flags)
> {
> struct tpm_output_header *header;
> int err;
>
> - len = tpm_transmit(chip, (u8 *) cmd, len);
> + len = tpm_transmit(chip, cmd, len, flags);
> if (len < 0)
> return len;
> else if (len < TPM_HEADER_SIZE)
> diff --git a/drivers/char/tpm/tpm.h b/drivers/char/tpm/tpm.h
> index 6e002c4..b9383fd 100644
> --- a/drivers/char/tpm/tpm.h
> +++ b/drivers/char/tpm/tpm.h
> @@ -476,12 +476,22 @@ extern dev_t tpm_devt;
> extern const struct file_operations tpm_fops;
> extern struct idr dev_nums_idr;
>
> +enum tpm_transmit_flags {
> + TPM_TRANSMIT_LOCK,
> +};
> +
> +ssize_t tpm_transmit(struct tpm_chip *chip, const char *buf,
> + size_t bufsiz, unsigned int flags);
> +ssize_t __tpm_transmit_cmd(struct tpm_chip *chip, void *cmd, int len,
> + const char *desc, unsigned int flags);
> +static inline ssize_t tpm_transmit_cmd(struct tpm_chip *chip, void *cmd,
> + int len, const char *desc)
> +{
> + return __tpm_transmit_cmd(chip, cmd, len, desc, TPM_TRANSMIT_LOCK);
> +}
> +
> ssize_t tpm_getcap(struct tpm_chip *chip, __be32 subcap_id, cap_t *cap,
> const char *desc);
> -ssize_t tpm_transmit(struct tpm_chip *chip, const char *buf,
> - size_t bufsiz);
By having also __tpm_transmit() the patch would be more localized, which
would make it easier to backport. I think I'll add that.
/Jarkko
> -ssize_t tpm_transmit_cmd(struct tpm_chip *chip, void *cmd, int len,
> - const char *desc);
> int tpm_get_timeouts(struct tpm_chip *chip);
> int tpm1_auto_startup(struct tpm_chip *chip);
> int tpm_do_selftest(struct tpm_chip *chip);
> diff --git a/drivers/char/tpm/tpm2-cmd.c b/drivers/char/tpm/tpm2-cmd.c
> index 499f405..99007d8 100644
> --- a/drivers/char/tpm/tpm2-cmd.c
> +++ b/drivers/char/tpm/tpm2-cmd.c
> @@ -576,7 +576,7 @@ static int tpm2_load(struct tpm_chip *chip,
> goto out;
> }
>
> - rc = tpm_transmit_cmd(chip, buf.data, PAGE_SIZE, "loading blob");
> + rc = __tpm_transmit_cmd(chip, buf.data, PAGE_SIZE, "loading blob", 0);
> if (!rc)
> *blob_handle = be32_to_cpup(
> (__be32 *) &buf.data[TPM_HEADER_SIZE]);
> @@ -604,7 +604,8 @@ static void tpm2_flush_context(struct tpm_chip *chip, u32 handle)
>
> tpm_buf_append_u32(&buf, handle);
>
> - rc = tpm_transmit_cmd(chip, buf.data, PAGE_SIZE, "flushing context");
> + rc = __tpm_transmit_cmd(chip, buf.data, PAGE_SIZE, "flushing context",
> + 0);
> if (rc)
> dev_warn(&chip->dev, "0x%08x was not flushed, rc=%d\n", handle,
> rc);
> @@ -635,7 +636,7 @@ static int tpm2_unseal(struct tpm_chip *chip,
> options->blobauth /* hmac */,
> TPM_DIGEST_SIZE);
>
> - rc = tpm_transmit_cmd(chip, buf.data, PAGE_SIZE, "unsealing");
> + rc = __tpm_transmit_cmd(chip, buf.data, PAGE_SIZE, "unsealing", 0);
> if (rc > 0)
> rc = -EPERM;
>
> @@ -668,13 +669,17 @@ int tpm2_unseal_trusted(struct tpm_chip *chip,
> u32 blob_handle;
> int rc;
>
> + mutex_lock(&chip->tpm_mutex);
> rc = tpm2_load(chip, payload, options, &blob_handle);
> - if (rc)
> + if (rc) {
> + mutex_unlock(&chip->tpm_mutex);
> return rc;
> + }
>
> rc = tpm2_unseal(chip, payload, options, blob_handle);
>
> tpm2_flush_context(chip, blob_handle);
> + mutex_unlock(&chip->tpm_mutex);
>
> return rc;
> }
> --
> 2.7.4
>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-security-module" in
> the body of a message to majordomo@xxxxxxxxxxxxxxx
> More majordomo info at http://vger.kernel.org/majordomo-info.html