tpm_crb: check for bad response size

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.

Cc: stable@vger.kernel.org
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>

diff --git a/drivers/char/tpm/tpm_crb.c b/drivers/char/tpm/tpm_crb.c
index 324561845dc2375a4264101851ab7454cbff44e2..1dfc37e33c02de7d86b289021b10625a2c3340a9 100644 (file)
--- a/drivers/char/tpm/tpm_crb.c
+++ b/drivers/char/tpm/tpm_crb.c
@@ -198,8 +198,7 @@ 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);