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    Subject[PATCH 5.1 093/138] tpm: Actually fail on TPM errors during "get random"
    Date
    From: Kees Cook <keescook@chromium.org>

    commit 782779b60faa2fc7ff609ac8ef938260fd792c0f upstream.

    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 <baker1tex@gmail.com>
    Reported-by: Craig Robson <craig@zhatt.com>
    Fixes: 7aee9c52d7ac ("tpm: tpm1: rewrite tpm1_get_random() using tpm_buf structure")
    Cc: Laura Abbott <labbott@redhat.com>
    Cc: Tomas Winkler <tomas.winkler@intel.com>
    Cc: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
    Cc: stable@vger.kernel.org
    Signed-off-by: Kees Cook <keescook@chromium.org>
    Reviewed-by: Tomas Winkler <tomas.winkler@intel.com>
    Tested-by: Bartosz Szczepanek <bsz@semihalf.com>
    Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
    Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/char/tpm/tpm1-cmd.c | 7 +++++--
    drivers/char/tpm/tpm2-cmd.c | 7 +++++--
    2 files changed, 10 insertions(+), 4 deletions(-)

    --- 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 *chi

    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];

    --- 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 *chi
    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];

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