[PATCH v2] HID: ft260: improve error handling of ft260_hid_feature_report_get()

[trix@redhat.com]

From: Tom Rix <trix@redhat.com>

Static analysis reports this representative problem

hid-ft260.c:787:9: warning: 4th function call argument is an
  uninitialized value
        return scnprintf(buf, PAGE_SIZE, "%hi\n", *field);
               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Uses of ft260_hid_feature_report_get() check if the return size matches
the requested size.  But the function can also fail with at least -ENOMEM.
Add the < 0 checks.

In ft260_hid_feature_report_get(), do not do the memcpy to the caller's
buffer if there is an error.

Fixes: 6a82582d9fa4 ("HID: ft260: add usb hid to i2c host bridge driver")
Signed-off-by: Tom Rix <trix@redhat.com>
---
v2:  add unlikely()'s for error conditions
---
 drivers/hid/hid-ft260.c | 39 ++++++++++++++++++++++++++++-----------
 1 file changed, 28 insertions(+), 11 deletions(-)

diff --git a/drivers/hid/hid-ft260.c b/drivers/hid/hid-ft260.c
index 7a9ba984a75a..7e881799d074 100644
--- a/drivers/hid/hid-ft260.c
+++ b/drivers/hid/hid-ft260.c
@@ -249,7 +249,8 @@ static int ft260_hid_feature_report_get(struct hid_device *hdev,
 
 	ret = hid_hw_raw_request(hdev, report_id, buf, len, HID_FEATURE_REPORT,
 				 HID_REQ_GET_REPORT);
-	memcpy(data, buf, len);
+	if (likely(ret == len))
+		memcpy(data, buf, len);
 	kfree(buf);
 	return ret;
 }
@@ -295,12 +296,16 @@ static int ft260_xfer_status(struct ft260_device *dev)
 	struct hid_device *hdev = dev->hdev;
 	struct ft260_get_i2c_status_report report;
 	int ret;
+	int len = sizeof(report);
 
 	ret = ft260_hid_feature_report_get(hdev, FT260_I2C_STATUS,
-					   (u8 *)&report, sizeof(report));
-	if (ret < 0) {
+					   (u8 *)&report, len);
+	if (unlikely(ret != len)) {
 		hid_err(hdev, "failed to retrieve status: %d\n", ret);
-		return ret;
+		if (ret >= 0)
+			return -EIO;
+		else
+			return ret;
 	}
 
 	dev->clock = le16_to_cpu(report.clock);
@@ -724,10 +729,12 @@ static int ft260_get_system_config(struct hid_device *hdev,
 
 	ret = ft260_hid_feature_report_get(hdev, FT260_SYSTEM_SETTINGS,
 					   (u8 *)cfg, len);
-	if (ret != len) {
+	if (unlikely(ret != len)) {
 		hid_err(hdev, "failed to retrieve system status\n");
 		if (ret >= 0)
 			return -EIO;
+		else
+			return ret;
 	}
 	return 0;
 }
@@ -780,8 +787,12 @@ static int ft260_byte_show(struct hid_device *hdev, int id, u8 *cfg, int len,
 	int ret;
 
 	ret = ft260_hid_feature_report_get(hdev, id, cfg, len);
-	if (ret != len && ret >= 0)
-		return -EIO;
+	if (unlikely(ret != len)) {
+		if (ret >= 0)
+			return -EIO;
+		else
+			return  ret;
+	}
 
 	return scnprintf(buf, PAGE_SIZE, "%hi\n", *field);
 }
@@ -792,8 +803,12 @@ static int ft260_word_show(struct hid_device *hdev, int id, u8 *cfg, int len,
 	int ret;
 
 	ret = ft260_hid_feature_report_get(hdev, id, cfg, len);
-	if (ret != len && ret >= 0)
-		return -EIO;
+	if (unlikely(ret != len)) {
+		if (ret >= 0)
+			return -EIO;
+		else
+			return ret;
+	}
 
 	return scnprintf(buf, PAGE_SIZE, "%hi\n", le16_to_cpu(*field));
 }
@@ -919,6 +934,7 @@ static int ft260_probe(struct hid_device *hdev, const struct hid_device_id *id)
 	struct ft260_device *dev;
 	struct ft260_get_chip_version_report version;
 	int ret;
+	int len;
 
 	dev = devm_kzalloc(&hdev->dev, sizeof(*dev), GFP_KERNEL);
 	if (!dev)
@@ -942,9 +958,10 @@ static int ft260_probe(struct hid_device *hdev, const struct hid_device_id *id)
 		goto err_hid_stop;
 	}
 
+	len = sizeof(version);
 	ret = ft260_hid_feature_report_get(hdev, FT260_CHIP_VERSION,
-					   (u8 *)&version, sizeof(version));
-	if (ret != sizeof(version)) {
+					   (u8 *)&version, len);
+	if (unlikely(ret != len)) {
 		hid_err(hdev, "failed to retrieve chip version\n");
 		if (ret >= 0)
 			ret = -EIO;
-- 
2.26.3