[PATCH 4.2 42/54] drm/dp/mst: make mst i2c transfer code more robust.

Greg Kroah-Hartman
2015-10-23T17:47:13Z

From: Dave Airlie <airlied@gmail.com>

commit ae491542cbbbcca0ec8938c37d4079a985e58440 upstream.

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

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/gpu/drm/drm_dp_mst_topology.c | 3 ++-
include/drm/drm_dp_mst_helper.h | 3 ++-
2 files changed, 4 insertions(+), 2 deletions(-)

--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -2789,12 +2789,13 @@ static int drm_dp_mst_i2c_xfer(struct i2
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;
--- 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;
};