tpm_tis: fix potential buffer overruns caused by bit glitches on the bus

commit 6bb320ca4a4a7b5b3db8c8d7250cc40002046878 upstream.

Discrete TPMs are often connected over slow serial buses which, on
some platforms, can have glitches causing bit flips.  In all the
driver _recv() functions, we need to use a u32 to unmarshal the
response size, otherwise a bit flip of the 31st bit would cause the
expected variable to go negative, which would then try to read a huge
amount of data.  Also sanity check that the expected amount of data is
large enough for the TPM header.

Signed-off-by: Jeremy Boone <jeremy.boone@nccgroup.trust>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
Tested-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: James Morris <james.morris@microsoft.com>
[bwh: Backported to 3.2: adjust filename]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/drivers/char/tpm/tpm_tis.c b/drivers/char/tpm/tpm_tis.c
index 0c4885d..34c60cd 100644 (file)
--- a/drivers/char/tpm/tpm_tis.c
+++ b/drivers/char/tpm/tpm_tis.c
@@ -253,7 +253,8 @@ static int recv_data(struct tpm_chip *chip, u8 *buf, size_t count)
 static int tpm_tis_recv(struct tpm_chip *chip, u8 *buf, size_t count)
 {
        int size = 0;
-       int expected, status;
+       int status;
+       u32 expected;
 
        if (count < TPM_HEADER_SIZE) {
                size = -EIO;
@@ -268,7 +269,7 @@ static int tpm_tis_recv(struct tpm_chip *chip, u8 *buf, size_t count)
        }
 
        expected = be32_to_cpu(*(__be32 *) (buf + 2));
-       if (expected > count) {
+       if (expected > count || expected < TPM_HEADER_SIZE) {
                size = -EIO;
                goto out;
        }