[PATCH] tpm: fix potential buffer overruns caused by bit glitches on the bus

[Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>]

From: Jeremy Boone <jeremy.boone@nccgroup.trust>

commit 3be23274755ee85771270a23af7691dc9b3a95db upstream

Discrete TPMs are often connected over slow serial buses which, on
some platforms, can have glitches causing bit flips.  If a bit does
flip it could cause an overrun if it's in one of the size parameters,
so sanity check that we're not overrunning the provided buffer when
doing a memcpy().

Signed-off-by: Jeremy Boone <jeremy.boone@nccgroup.trust>
Cc: stable@vger.kernel.org
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Tested-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
---
Backported to v4.9
v2: fixed the upstream ID
 drivers/char/tpm/tpm-interface.c | 5 +++++
 drivers/char/tpm/tpm2-cmd.c      | 6 ++++++
 2 files changed, 11 insertions(+)

diff --git a/drivers/char/tpm/tpm-interface.c b/drivers/char/tpm/tpm-interface.c
index d0ac2d56520f..830d7e30e508 100644
--- a/drivers/char/tpm/tpm-interface.c
+++ b/drivers/char/tpm/tpm-interface.c
@@ -1078,6 +1078,11 @@ int tpm_get_random(u32 chip_num, u8 *out, size_t max)
 			break;
 
 		recd = be32_to_cpu(tpm_cmd.params.getrandom_out.rng_data_len);
+		if (recd > num_bytes) {
+			total = -EFAULT;
+			break;
+		}
+
 		memcpy(dest, tpm_cmd.params.getrandom_out.rng_data, recd);
 
 		dest += recd;
diff --git a/drivers/char/tpm/tpm2-cmd.c b/drivers/char/tpm/tpm2-cmd.c
index 17896d654033..a5780ebe15ef 100644
--- a/drivers/char/tpm/tpm2-cmd.c
+++ b/drivers/char/tpm/tpm2-cmd.c
@@ -668,6 +668,11 @@ static int tpm2_unseal_cmd(struct tpm_chip *chip,
 	if (!rc) {
 		data_len = be16_to_cpup(
 			(__be16 *) &buf.data[TPM_HEADER_SIZE + 4]);
+		if (data_len < MIN_KEY_SIZE ||  data_len > MAX_KEY_SIZE + 1) {
+			rc = -EFAULT;
+			goto out;
+		}
+
 		data = &buf.data[TPM_HEADER_SIZE + 6];
 
 		memcpy(payload->key, data, data_len - 1);
@@ -675,6 +680,7 @@ static int tpm2_unseal_cmd(struct tpm_chip *chip,
 		payload->migratable = data[data_len - 1];
 	}
 
+out:
 	tpm_buf_destroy(&buf);
 	return rc;
 }
-- 
2.15.1