Re: [PATCH v3] tpm: Actually fail on TPM errors during "get random"
From: Laura Abbott
Date: Tue May 28 2019 - 15:06:17 EST
On 4/3/19 1:52 PM, Jarkko Sakkinen wrote:
On Tue, Apr 02, 2019 at 07:13:52PM +0000, Winkler, Tomas wrote:
On Tue, Apr 02, 2019 at 02:46:25AM +0300, Jarkko Sakkinen wrote:
On Mon, Apr 01, 2019 at 12:06:07PM -0700, Kees Cook wrote:
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>
---
v3: fix never-succeed, limit checks to tpm cmd return (James, Jason)
v2: also fix tpm2 implementation (Jason Gunthorpe)
---
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
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@xxxxxxxxxxxxxxx>
Applied to my master branch. Jason, Tomas, do you want me to add reviewed-
by's?
Sure, it fixes my patch.
Great, I'll add it. Thank you. Just want to be explicit with these
things as I consider them as if I was asking a signature from someone
:-)
/Jarkko
Was this intended to go in for 5.2? I still don't see it in the tree.
Thanks,
Laura