drm/dp/mst: Validate REMOTE_I2C_READ harder

Make sure i2c msgs we're asked to transfer conform to the
requirements of REMOTE_I2C_READ. We were only checking that the
last message is a read, but we must also check that the preceding
messages are all writes. Also check that the length of each
message isn't too long.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180928180403.22499-2-ville.syrjala@linux.intel.com
Reviewed-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>

diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
index 229ad60..f0cbd5f 100644 (file)
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -3250,6 +3250,23 @@ void drm_dp_mst_topology_mgr_destroy(struct drm_dp_mst_topology_mgr *mgr)
 }
 EXPORT_SYMBOL(drm_dp_mst_topology_mgr_destroy);
 
+static bool remote_i2c_read_ok(const struct i2c_msg msgs[], int num)
+{
+       int i;
+
+       if (num - 1 > DP_REMOTE_I2C_READ_MAX_TRANSACTIONS)
+               return false;
+
+       for (i = 0; i < num - 1; i++) {
+               if (msgs[i].flags & I2C_M_RD ||
+                   msgs[i].len > 0xff)
+                       return false;
+       }
+
+       return msgs[num - 1].flags & I2C_M_RD &&
+               msgs[num - 1].len <= 0xff;
+}
+
 /* I2C device */
 static int drm_dp_mst_i2c_xfer(struct i2c_adapter *adapter, struct i2c_msg *msgs,
                               int num)
@@ -3259,7 +3276,6 @@ static int drm_dp_mst_i2c_xfer(struct i2c_adapter *adapter, struct i2c_msg *msgs
        struct drm_dp_mst_branch *mstb;
        struct drm_dp_mst_topology_mgr *mgr = port->mgr;
        unsigned int i;
-       bool reading = false;
        struct drm_dp_sideband_msg_req_body msg;
        struct drm_dp_sideband_msg_tx *txmsg = NULL;
        int ret;
@@ -3268,12 +3284,7 @@ static int drm_dp_mst_i2c_xfer(struct i2c_adapter *adapter, struct i2c_msg *msgs
        if (!mstb)
                return -EREMOTEIO;
 
-       /* construct i2c msg */
-       /* see if last msg is a read */
-       if (msgs[num - 1].flags & I2C_M_RD)
-               reading = true;
-
-       if (!reading || (num - 1 > DP_REMOTE_I2C_READ_MAX_TRANSACTIONS)) {
+       if (!remote_i2c_read_ok(msgs, num)) {
                DRM_DEBUG_KMS("Unsupported I2C transaction for MST device\n");
                ret = -EIO;
                goto out;