[S390] zcrypt: add sanity check before copy_from_user()

It's not obvious that copy_from_user() is called with a sane length
parameter here. Even though it currently seems to be correct better
add a check to prevent stack corruption / exploits.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

1 files changed, 3 insertions, 1 deletions

diff --git a/drivers/s390/crypto/zcrypt_api.c b/drivers/s390/crypto/zcrypt_api.c
index 0d4d18bdd45c..c68be24e27d9 100644
--- a/drivers/s390/crypto/zcrypt_api.c
+++ b/drivers/s390/crypto/zcrypt_api.c
@@ -393,10 +393,12 @@ static long zcrypt_rsa_crt(struct ica_rsa_modexpo_crt *crt)
                          * u_mult_inv > 128 bytes.
                          */
                         if (copied == 0) {
-                                int len;
+                                unsigned int len;
                                 spin_unlock_bh(&zcrypt_device_lock);
                                 /* len is max 256 / 2 - 120 = 8 */
                                 len = crt->inputdatalength / 2 - 120;
+                                if (len > sizeof(z1))
+                                        return -EFAULT;
                                 z1 = z2 = z3 = 0;
                                 if (copy_from_user(&z1, crt->np_prime, len) ||
                                     copy_from_user(&z2, crt->bp_key, len) ||