platform/chrome: cros_ec_dev - Fix security issue

Prevent memory scribble by checking that ioctl buffer size parameters
are sane.
Without this check, on 32 bits system, if .insize = 0xffffffff - 20 and
.outsize the amount to scribble, we would overflow, allocate a small
amounts and be able to write outside of the malloc'ed area.
Adding a hard limit allows argument checking of the ioctl. With the
current EC, it is expected .insize and .outsize to be at around 512 bytes
or less.

Signed-off-by: Gwendal Grignou <gwendal@chromium.org>
Signed-off-by: Olof Johansson <olof@lixom.net>

diff --git a/drivers/platform/chrome/cros_ec_dev.c b/drivers/platform/chrome/cros_ec_dev.c
index d45cd25..187470c 100644 (file)
--- a/drivers/platform/chrome/cros_ec_dev.c
+++ b/drivers/platform/chrome/cros_ec_dev.c
@@ -137,6 +137,10 @@ static long ec_device_ioctl_xcmd(struct cros_ec_dev *ec, void __user *arg)
        if (copy_from_user(&u_cmd, arg, sizeof(u_cmd)))
                return -EFAULT;
 
+       if ((u_cmd.outsize > EC_MAX_MSG_BYTES) ||
+           (u_cmd.insize > EC_MAX_MSG_BYTES))
+               return -EINVAL;
+
        s_cmd = kmalloc(sizeof(*s_cmd) + max(u_cmd.outsize, u_cmd.insize),
                        GFP_KERNEL);
        if (!s_cmd)

diff --git a/drivers/platform/chrome/cros_ec_proto.c b/drivers/platform/chrome/cros_ec_proto.c
index 990308c..b6e161f 100644 (file)
--- a/drivers/platform/chrome/cros_ec_proto.c
+++ b/drivers/platform/chrome/cros_ec_proto.c
@@ -298,8 +298,8 @@ int cros_ec_query_all(struct cros_ec_device *ec_dev)
                        ec_dev->max_response = EC_PROTO2_MAX_PARAM_SIZE;
                        ec_dev->max_passthru = 0;
                        ec_dev->pkt_xfer = NULL;
-                       ec_dev->din_size = EC_MSG_BYTES;
-                       ec_dev->dout_size = EC_MSG_BYTES;
+                       ec_dev->din_size = EC_PROTO2_MSG_BYTES;
+                       ec_dev->dout_size = EC_PROTO2_MSG_BYTES;
                } else {
                        /*
                         * It's possible for a test to occur too early when

diff --git a/include/linux/mfd/cros_ec.h b/include/linux/mfd/cros_ec.h
index a677c2b..64184d2 100644 (file)
--- a/include/linux/mfd/cros_ec.h
+++ b/include/linux/mfd/cros_ec.h
@@ -50,9 +50,11 @@ enum {
                                        EC_MSG_TX_TRAILER_BYTES,
        EC_MSG_RX_PROTO_BYTES   = 3,
 
-       /* Max length of messages */
-       EC_MSG_BYTES            = EC_PROTO2_MAX_PARAM_SIZE +
+       /* Max length of messages for proto 2*/
+       EC_PROTO2_MSG_BYTES             = EC_PROTO2_MAX_PARAM_SIZE +
                                        EC_MSG_TX_PROTO_BYTES,
+
+       EC_MAX_MSG_BYTES                = 64 * 1024,
 };
 
 /*