>
> A "get random" may fail with a TPM error, but those codes were returned as-is
> to the caller, which assumed the result was the number of bytes that had been
> written to the target buffer, which could lead to a kernel heap memory
> exposure and over-read.
>
> This fixes tpm1_get_random() to mask positive TPM errors into -EIO, as before.
>
> [ 18.092103] tpm tpm0: A TPM error (379) occurred attempting get random
> [ 18.092106] usercopy: Kernel memory exposure attempt detected from SLUB
> object 'kmalloc-64' (offset 0, size 379)!
>
> Link: https://bugzilla.redhat.com/show_bug.cgi?id=1650989
> Reported-by: Phil Baker <baker1...@gmail.com>
> Reported-by: Craig Robson <cr...@zhatt.com>
> Fixes: 7aee9c52d7ac ("tpm: tpm1: rewrite tpm1_get_random() using tpm_buf
> structure")
> Cc: Laura Abbott <labb...@redhat.com>
> Cc: Tomas Winkler <tomas.wink...@intel.com>
> Cc: Jarkko Sakkinen <jarkko.sakki...@linux.intel.com>
> Cc: sta...@vger.kernel.org
> Signed-off-by: Kees Cook <keesc...@chromium.org>
> ---
> v3: fix never-succeed, limit checks to tpm cmd return (James, Jason)
> v2: also fix tpm2 implementation (Jason Gunthorpe)
Looks good to me.
Thanks
Tomas
> ---
> drivers/char/tpm/tpm1-cmd.c | 7 +++++-- drivers/char/tpm/tpm2-cmd.c | 7
> +++++--
> 2 files changed, 10 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/char/tpm/tpm1-cmd.c b/drivers/char/tpm/tpm1-cmd.c
> index 85dcf2654d11..faacbe1ffa1a 100644
> --- a/drivers/char/tpm/tpm1-cmd.c
> +++ b/drivers/char/tpm/tpm1-cmd.c
> @@ -510,7 +510,7 @@ struct tpm1_get_random_out {
> *
> * Return:
> * * number of bytes read
> - * * -errno or a TPM return code otherwise
> + * * -errno (positive TPM return codes are masked to -EIO)
> */
> int tpm1_get_random(struct tpm_chip *chip, u8 *dest, size_t max) { @@ -
> 531,8 +531,11 @@ int tpm1_get_random(struct tpm_chip *chip, u8 *dest,
> size_t max)
>
> rc = tpm_transmit_cmd(chip, &buf, sizeof(out->rng_data_len),
> "attempting get random");
> - if (rc)
> + if (rc) {
> + if (rc > 0)
> + rc = -EIO;
> goto out;
> + }
>
> out = (struct tpm1_get_random_out
> *)&buf.data[TPM_HEADER_SIZE];
>
> diff --git a/drivers/char/tpm/tpm2-cmd.c b/drivers/char/tpm/tpm2-cmd.c
> index e74c5b7b64bf..8ffa6af61580 100644
> --- a/drivers/char/tpm/tpm2-cmd.c
> +++ b/drivers/char/tpm/tpm2-cmd.c
> @@ -301,7 +301,7 @@ struct tpm2_get_random_out {
> *
> * Return:
> * size of the buffer on success,
> - * -errno otherwise
> + * -errno otherwise ((positive TPM return codes are masked to -EIO)
> */
> int tpm2_get_random(struct tpm_chip *chip, u8 *dest, size_t max) { @@ -
> 328,8 +328,11 @@ int tpm2_get_random(struct tpm_chip *chip, u8 *dest,
> size_t max)
> offsetof(struct tpm2_get_random_out,
> buffer),
> "attempting get random");
> - if (err)
> + if (err) {
> + if (err > 0)
> + err = -EIO;
> goto out;
> + }
>
> out = (struct tpm2_get_random_out *)
> &buf.data[TPM_HEADER_SIZE];
> --
> 2.17.1
>
>
> --
> Kees Cook
