[PATCH] tpm: fix response size validation in tpm_get_random()

When checking whether the response is large enough to be able to contain
the received random bytes in tpm_get_random() and tpm2_get_random(),
they fail to take account the header size, which should be added to the
minimum size. This commit fixes this issue.

Cc: stable at vger.kernel.org
Fixes: c659af78eb7b ("tpm: Check size of response before accessing data")
Signed-off-by: Jarkko Sakkinen <redacted>
---
  drivers/char/tpm/tpm-interface.c | 3 ++-
  drivers/char/tpm/tpm2-cmd.c      | 4 +++-
  2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/char/tpm/tpm-interface.c b/drivers/char/tpm/tpm-interface.c
index 1a803b0cf980..318a7078b2ba 100644
--- a/drivers/char/tpm/tpm-interface.c
+++ b/drivers/char/tpm/tpm-interface.c

@@ -1321,7 +1321,8 @@ int tpm_get_random(struct tpm_chip *chip, u8 *out, size_t max)
  		}

  		rlength = be32_to_cpu(tpm_cmd.header.out.length);
-		if (rlength < offsetof(struct tpm_getrandom_out, rng_data) +
+		if (rlength < TPM_HEADER_SIZE +
+			      offsetof(struct tpm_getrandom_out, rng_data) +
  			      recd) {
  			total = -EFAULT;
  			break;

diff --git a/drivers/char/tpm/tpm2-cmd.c b/drivers/char/tpm/tpm2-cmd.c
index c31b490bd41d..3acf4fd4e5a5 100644
--- a/drivers/char/tpm/tpm2-cmd.c
+++ b/drivers/char/tpm/tpm2-cmd.c

@@ -329,7 +329,9 @@ int tpm2_get_random(struct tpm_chip *chip, u8 *dest, size_t max)
  			&buf.data[TPM_HEADER_SIZE];
  		recd = min_t(u32, be16_to_cpu(out->size), num_bytes);
  		if (tpm_buf_length(&buf) <
-		    offsetof(struct tpm2_get_random_out, buffer) + recd) {
+		    TPM_HEADER_SIZE +
+		    offsetof(struct tpm2_get_random_out, buffer) +
+		    recd) {
  			err = -EFAULT;
  			goto out;
  		}