[PATCH 5.1 093/138] tpm: Actually fail on TPM errors during "get random"

From: Greg Kroah-Hartman
Date: Fri Jul 12 2019 - 08:29:20 EST


From: Kees Cook <keescook@xxxxxxxxxxxx>

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@xxxxxxxxx>
Reported-by: Craig Robson <craig@xxxxxxxxx>
Fixes: 7aee9c52d7ac ("tpm: tpm1: rewrite tpm1_get_random() using tpm_buf structure")
Cc: Laura Abbott <labbott@xxxxxxxxxx>
Cc: Tomas Winkler <tomas.winkler@xxxxxxxxx>
Cc: Jarkko Sakkinen <jarkko.sakkinen@xxxxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
Reviewed-by: Tomas Winkler <tomas.winkler@xxxxxxxxx>
Tested-by: Bartosz Szczepanek <bsz@xxxxxxxxxxxx>
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@xxxxxxxxxxxxxxx>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@xxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
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];