Re: [PATCH] KEYS: trusted: allow module init if TPM is inactive or deactivated
From: Tyler Hicks <hidden>
Date: 2019-07-08 19:55:47
Also in:
keyrings, linux-integrity, lkml
On 2019-07-05 18:37:35, Roberto Sassu wrote:
quoted hunk ↗ jump to hunk
Commit c78719203fc6 ("KEYS: trusted: allow trusted.ko to initialize w/o a TPM") allows the trusted module to be loaded even a TPM is not found to avoid module dependency problems. Unfortunately, this does not completely solve the issue, as there could be a case where a TPM is found but is not functional (the TPM commands return an error). Specifically, after the tpm_chip structure is returned by tpm_default_chip() in init_trusted(), the execution terminates after init_digests() returns -EFAULT (due to the fact that tpm_get_random() returns a positive value, but less than TPM_MAX_DIGEST_SIZE). This patch fixes the issue by ignoring the TPM_ERR_DEACTIVATED and TPM_ERR_DISABLED errors. Fixes: 240730437deb ("KEYS: trusted: explicitly use tpm_chip structure...") Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com> --- drivers/char/tpm/tpm.h | 2 -- include/linux/tpm.h | 3 +++ security/keys/trusted.c | 6 +++++- 3 files changed, 8 insertions(+), 3 deletions(-)diff --git a/drivers/char/tpm/tpm.h b/drivers/char/tpm/tpm.h index e503ffc3aa39..a216ac396711 100644 --- a/drivers/char/tpm/tpm.h +++ b/drivers/char/tpm/tpm.h@@ -54,8 +54,6 @@ enum tpm_addr { #define TPM_WARN_RETRY 0x800 #define TPM_WARN_DOING_SELFTEST 0x802 -#define TPM_ERR_DEACTIVATED 0x6 -#define TPM_ERR_DISABLED 0x7 #define TPM_ERR_INVALID_POSTINIT 38 #define TPM_HEADER_SIZE 10diff --git a/include/linux/tpm.h b/include/linux/tpm.h index 53c0ea9ec9df..efd3ccbb6aee 100644 --- a/include/linux/tpm.h +++ b/include/linux/tpm.h@@ -26,6 +26,9 @@ #define TPM_DIGEST_SIZE 20 /* Max TPM v1.2 PCR size */ #define TPM_MAX_DIGEST_SIZE SHA512_DIGEST_SIZE +#define TPM_ERR_DEACTIVATED 0x6 +#define TPM_ERR_DISABLED 0x7 + struct tpm_chip; struct trusted_key_payload; struct trusted_key_options;diff --git a/security/keys/trusted.c b/security/keys/trusted.c index 9a94672e7adc..430d85090b3b 100644 --- a/security/keys/trusted.c +++ b/security/keys/trusted.c@@ -389,6 +389,10 @@ static int pcrlock(const int pcrnum) if (!capable(CAP_SYS_ADMIN)) return -EPERM; + /* This can happen if the TPM is inactive. */ + if (!digests) + return -EINVAL; + return tpm_pcr_extend(chip, pcrnum, digests) ? -EINVAL : 0; }@@ -1233,7 +1237,7 @@ static int __init init_digests(void) int i; ret = tpm_get_random(chip, digest, TPM_MAX_DIGEST_SIZE); - if (ret < 0) + if (ret < 0 || ret == TPM_ERR_DEACTIVATED || ret == TPM_ERR_DISABLED) return ret;
As someone who hasn't looked at much of the TPM code, I would have expected tpm_get_random() to return a positive value that only ever indicates the number of random bytes saved to the buffer. From the function documentation: Return: number of random bytes read or a negative error value. Despite the function documentation and as your patch suggests, I can see that it is possible for tpm_transmit_cmd() to return a positive value that's also returned by tpm_get_random() even though it may not have filled the buffer when the TPM is in an inactive/deactivated state. I think there are other callers which are not prepared for positive return values that indicate a failure to fill the buffer with random data. For instance, the way that tpm_hwrng_read() is calling tpm_get_random() looks a little worrisome. This patch would likely fix the bug reported against eCryptfs (https://bugzilla.kernel.org/show_bug.cgi?id=203953) but I can't help to think that callers of tpm_get_random() would benefit from a more consolidated approach of handling TPM_ERR_* return values rather than handling them at this single call site. Tyler
if (ret < TPM_MAX_DIGEST_SIZE) return -EFAULT; -- 2.17.1