HID: i2c-hid: fix race condition reading reports

Current driver uses a common buffer for reading reports either
synchronously in i2c_hid_get_raw_report() and asynchronously in
the interrupt handler.
There is race condition if an interrupt arrives immediately after
the report is received in i2c_hid_get_raw_report(); the common
buffer is modified by the interrupt handler with the new report
and then i2c_hid_get_raw_report() proceed using wrong data.

Fix it by using a separate buffers for synchronous reports.
Signed-off-by: Jean-Baptiste Maneyrol <jmaneyrol@invensense.com>
[Antonio Borneo: cleanup, rebase to v3.17, submit mainline]
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/hid/i2c-hid/i2c-hid.c

@@ -137,6 +137,7 @@ struct i2c_hid {
 						   * descriptor. */
 	unsigned int		bufsize;	/* i2c buffer size */
 	char			*inbuf;		/* Input buffer */
+	char			*rawbuf;	/* Raw Input buffer */
 	char			*cmdbuf;	/* Command buffer */
 	char			*argsbuf;	/* Command arguments buffer */
 
@@ -504,9 +505,11 @@ static void i2c_hid_find_max_report(struct hid_device *hid, unsigned int type,
 static void i2c_hid_free_buffers(struct i2c_hid *ihid)
 {
 	kfree(ihid->inbuf);
+	kfree(ihid->rawbuf);
 	kfree(ihid->argsbuf);
 	kfree(ihid->cmdbuf);
 	ihid->inbuf = NULL;
+	ihid->rawbuf = NULL;
 	ihid->cmdbuf = NULL;
 	ihid->argsbuf = NULL;
 	ihid->bufsize = 0;
@@ -522,10 +525,11 @@ static int i2c_hid_alloc_buffers(struct i2c_hid *ihid, size_t report_size)
 		       report_size; /* report */
 
 	ihid->inbuf = kzalloc(report_size, GFP_KERNEL);
+	ihid->rawbuf = kzalloc(report_size, GFP_KERNEL);
 	ihid->argsbuf = kzalloc(args_len, GFP_KERNEL);
 	ihid->cmdbuf = kzalloc(sizeof(union command) + args_len, GFP_KERNEL);
 
-	if (!ihid->inbuf || !ihid->argsbuf || !ihid->cmdbuf) {
+	if (!ihid->inbuf || !ihid->rawbuf || !ihid->argsbuf || !ihid->cmdbuf) {
 		i2c_hid_free_buffers(ihid);
 		return -ENOMEM;
 	}
@@ -552,12 +556,12 @@ static int i2c_hid_get_raw_report(struct hid_device *hid,
 
 	ret = i2c_hid_get_report(client,
 			report_type == HID_FEATURE_REPORT ? 0x03 : 0x01,
-			report_number, ihid->inbuf, ask_count);
+			report_number, ihid->rawbuf, ask_count);
 
 	if (ret < 0)
 		return ret;
 
-	ret_count = ihid->inbuf[0] | (ihid->inbuf[1] << 8);
+	ret_count = ihid->rawbuf[0] | (ihid->rawbuf[1] << 8);
 
 	if (ret_count <= 2)
 		return 0;
@@ -566,7 +570,7 @@ static int i2c_hid_get_raw_report(struct hid_device *hid,
 
 	/* The query buffer contains the size, dropping it in the reply */
 	count = min(count, ret_count - 2);
-	memcpy(buf, ihid->inbuf + 2, count);
+	memcpy(buf, ihid->rawbuf + 2, count);
 
 	return count;
 }