Re: [PATCH] Input elan_i2c_smbus - Fix more potential stack buffer overflows

On Tue, Jun 19, 2018 at 02:05:14PM +0200, Benjamin Tissoires wrote:

On Mon, Jun 18, 2018 at 7:56 PM, Ben Hutchings
[off-list ref] wrote:

quoted

Commit 40f7090bb1b4 ("Input: elan_i2c_smbus - fix corrupted stack")
fixed most of the functions using i2c_smbus_read_block_data() to
allocate a buffer with the maximum block size.  However three
functions were left unchanged:

* In elan_smbus_initialize(), increase the buffer size in the same
  way.
* In elan_smbus_calibrate_result(), the buffer is provided by the
  caller (calibrate_store()), so introduce a bounce buffer.  Also
  name the result buffer size.
* In elan_smbus_get_report(), the buffer is provided by the caller
  but happens to be the right length.  Add a compile-time assertion
  to ensure this remains the case.

Cc: <redacted> # 3.19+
Signed-off-by: Ben Hutchings <redacted>
---
This is compile-tested only.

[adding KT in Cc]

We are currently testing the Lenovo P52, and this patch seems to
behave well. We have other issues with the P52, but unrelated to this
patch.

Reviewed-by: Benjamin Tissoires <redacted>

Applied, thank you.

Cheers,
Benjamin

quoted

Ben.

 drivers/input/mouse/elan_i2c.h       |  2 ++
 drivers/input/mouse/elan_i2c_core.c  |  2 +-
 drivers/input/mouse/elan_i2c_smbus.c | 10 ++++++++--
 3 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/drivers/input/mouse/elan_i2c.h b/drivers/input/mouse/elan_i2c.h
index 599544c1a91c..243e0fa6e3e3 100644
--- a/drivers/input/mouse/elan_i2c.h
+++ b/drivers/input/mouse/elan_i2c.h

@@ -27,6 +27,8 @@
 #define ETP_DISABLE_POWER      0x0001
 #define ETP_PRESSURE_OFFSET    25

+#define ETP_CALIBRATE_MAX_LEN  3
+
 /* IAP Firmware handling */
 #define ETP_PRODUCT_ID_FORMAT_STRING   "%d.0"
 #define ETP_FW_NAME            "elan_i2c_" ETP_PRODUCT_ID_FORMAT_STRING ".bin"

diff --git a/drivers/input/mouse/elan_i2c_core.c b/drivers/input/mouse/elan_i2c_core.c
index 75e757520ef0..d5f74dd7e23b 100644
--- a/drivers/input/mouse/elan_i2c_core.c
+++ b/drivers/input/mouse/elan_i2c_core.c

@@ -610,7 +610,7 @@ static ssize_t calibrate_store(struct device *dev,
        int tries = 20;
        int retval;
        int error;
-       u8 val[3];
+       u8 val[ETP_CALIBRATE_MAX_LEN];

        retval = mutex_lock_interruptible(&data->sysfs_mutex);
        if (retval)

diff --git a/drivers/input/mouse/elan_i2c_smbus.c b/drivers/input/mouse/elan_i2c_smbus.c
index cfcb32559925..c060d270bc4d 100644
--- a/drivers/input/mouse/elan_i2c_smbus.c
+++ b/drivers/input/mouse/elan_i2c_smbus.c

@@ -56,7 +56,7 @@
 static int elan_smbus_initialize(struct i2c_client *client)
 {
        u8 check[ETP_SMBUS_HELLOPACKET_LEN] = { 0x55, 0x55, 0x55, 0x55, 0x55 };
-       u8 values[ETP_SMBUS_HELLOPACKET_LEN] = { 0, 0, 0, 0, 0 };
+       u8 values[I2C_SMBUS_BLOCK_MAX] = {0};
        int len, error;

        /* Get hello packet */

@@ -117,12 +117,16 @@ static int elan_smbus_calibrate(struct i2c_client *client)
 static int elan_smbus_calibrate_result(struct i2c_client *client, u8 *val)
 {
        int error;
+       u8 buf[I2C_SMBUS_BLOCK_MAX] = {0};
+
+       BUILD_BUG_ON(ETP_CALIBRATE_MAX_LEN > sizeof(buf));

        error = i2c_smbus_read_block_data(client,
-                                         ETP_SMBUS_CALIBRATE_QUERY, val);
+                                         ETP_SMBUS_CALIBRATE_QUERY, buf);
        if (error < 0)
                return error;

+       memcpy(val, buf, ETP_CALIBRATE_MAX_LEN);
        return 0;
 }

@@ -472,6 +476,8 @@ static int elan_smbus_get_report(struct i2c_client *client, u8 *report)
 {
        int len;

+       BUILD_BUG_ON(I2C_SMBUS_BLOCK_MAX > ETP_SMBUS_REPORT_LEN);
+
        len = i2c_smbus_read_block_data(client,
                                        ETP_SMBUS_PACKET_QUERY,
                                        &report[ETP_SMBUS_REPORT_OFFSET]);
--

Ben Hutchings, Software Developer                         Codethink Ltd
https://www.codethink.co.uk/                 Dale House, 35 Dale Street
                                     Manchester, M1 2HF, United Kingdom

-- 
Dmitry