Re: [PATCH v3] tpm: Actually fail on TPM errors during "get random"

[Laura Abbott <labbott@redhat.com>]

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@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>
>>>>> ---
>>>>> 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@linux.intel.com>
>>>
>>> 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