drm/dp/mst: make mst i2c transfer code more robust.

This zeroes the msg so no random stack data ends up getting
sent, it also limits the function to not accepting > 4
i2c msgs.

Cc: stable@vger.kernel.org
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Dave Airlie <airlied@redhat.com>

diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
index bf27a07dbce36993e7ed668ff567f5565a6e0995..5bca390d9ae26022df1be85d008ee7107d8aa9b8 100644 (file)
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -2801,12 +2801,13 @@ static int drm_dp_mst_i2c_xfer(struct i2c_adapter *adapter, struct i2c_msg *msgs
        if (msgs[num - 1].flags & I2C_M_RD)
                reading = true;
 
-       if (!reading) {
+       if (!reading || (num - 1 > DP_REMOTE_I2C_READ_MAX_TRANSACTIONS)) {
                DRM_DEBUG_KMS("Unsupported I2C transaction for MST device\n");
                ret = -EIO;
                goto out;
        }
 
+       memset(&msg, 0, sizeof(msg));
        msg.req_type = DP_REMOTE_I2C_READ;
        msg.u.i2c_read.num_transactions = num - 1;
        msg.u.i2c_read.port_number = port->port_num;

diff --git a/include/drm/drm_dp_mst_helper.h b/include/drm/drm_dp_mst_helper.h
index 0f408b002d989ee8bca9489d6c1add673b315a51..5340099741aec8c48575b1c1056f23903e150ed6 100644 (file)
--- a/include/drm/drm_dp_mst_helper.h
+++ b/include/drm/drm_dp_mst_helper.h
@@ -253,6 +253,7 @@ struct drm_dp_remote_dpcd_write {
        u8 *bytes;
 };
 
+#define DP_REMOTE_I2C_READ_MAX_TRANSACTIONS 4
 struct drm_dp_remote_i2c_read {
        u8 num_transactions;
        u8 port_number;
@@ -262,7 +263,7 @@ struct drm_dp_remote_i2c_read {
                u8 *bytes;
                u8 no_stop_bit;
                u8 i2c_transaction_delay;
-       } transactions[4];
+       } transactions[DP_REMOTE_I2C_READ_MAX_TRANSACTIONS];
        u8 read_i2c_device_id;
        u8 num_bytes_read;
 };