From: Kees Cook <keesc...@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 <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> Reviewed-by: Tomas Winkler <tomas.wink...@intel.com> Tested-by: Bartosz Szczepanek <b...@semihalf.com> Reviewed-by: Jarkko Sakkinen <jarkko.sakki...@linux.intel.com> Signed-off-by: Jarkko Sakkinen <jarkko.sakki...@linux.intel.com> Signed-off-by: Greg Kroah-Hartman <gre...@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 @@ -297,7 +297,7 @@ 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) { @@ -324,8 +324,11 @@ 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];
