TSS_checkhmac1() and TSS_checkhmac2() silently return success when the response tag is TPM_TAG_RSP_COMMAND (0x00c4), bypassing HMAC verification entirely. A forged TPM response with this unauthenticated tag allows an attacker to skip integrity checks on TPM responses.
Reject TPM_TAG_RSP_COMMAND with -EINVAL in both functions, requiring all responses to carry a proper authenticated tag. Signed-off-by: Sanket Sharma <[email protected]> --- security/keys/trusted-keys/trusted_tpm1.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/security/keys/trusted-keys/trusted_tpm1.c b/security/keys/trusted-keys/trusted_tpm1.c index d47cb7108..c89fc6cfe 100644 --- a/security/keys/trusted-keys/trusted_tpm1.c +++ b/security/keys/trusted-keys/trusted_tpm1.c @@ -202,7 +202,7 @@ static int TSS_checkhmac1(unsigned char *buffer, ordinal = command; result = LOAD32N(buffer, TPM_RETURN_OFFSET); if (tag == TPM_TAG_RSP_COMMAND) - return 0; + return -EINVAL; if (tag != TPM_TAG_RSP_AUTH1_COMMAND) return -EINVAL; authdata = buffer + bufsize - SHA1_DIGEST_SIZE; @@ -270,7 +270,7 @@ static int TSS_checkhmac2(unsigned char *buffer, result = LOAD32N(buffer, TPM_RETURN_OFFSET); if (tag == TPM_TAG_RSP_COMMAND) - return 0; + return -EINVAL; if (tag != TPM_TAG_RSP_AUTH2_COMMAND) return -EINVAL; authdata1 = buffer + bufsize - (SHA1_DIGEST_SIZE + 1 -- 2.53.0
