tpm_crb: check for bad response size

commit 8569defde8057258835c51ce01a33de82e14b148 upstream.

Make sure size of response buffer is at least 6 bytes, or
we will underflow and pass large size_t to memcpy_fromio().
This was encountered while testing earlier version of
locality patchset.

Fixes: 30fc8d138e912 ("tpm: TPM 2.0 CRB Interface")
Signed-off-by: Jerry Snitselaar <jsnitsel@redhat.com>
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 1 insertions, 2 deletions

diff --git a/drivers/char/tpm/tpm_crb.c b/drivers/char/tpm/tpm_crb.c
index a7c870af916c..fa0f66809503 100644
--- a/drivers/char/tpm/tpm_crb.c
+++ b/drivers/char/tpm/tpm_crb.c
@@ -111,8 +111,7 @@ static int crb_recv(struct tpm_chip *chip, u8 *buf, size_t count)
 
         memcpy_fromio(buf, priv->rsp, 6);
         expected = be32_to_cpup((__be32 *) &buf[2]);
-
-        if (expected > count)
+        if (expected > count || expected < 6)
                 return -EIO;
 
         memcpy_fromio(&buf[6], &priv->rsp[6], expected - 6);