[PATCH 4.14 15/22] comedi: dt9812: fix DMA buffers on stack

[Greg Kroah-Hartman]

From: Johan Hovold <johan@xxxxxxxxxx>

commit 536de747bc48262225889a533db6650731ab25d3 upstream.

USB transfer buffers are typically mapped for DMA and must not be
allocated on the stack or transfers will fail.

Allocate proper transfer buffers in the various command helpers and
return an error on short transfers instead of acting on random stack
data.

Note that this also fixes a stack info leak on systems where DMA is not
used as 32 bytes are always sent to the device regardless of how short
the command is.

Fixes: 63274cd7d38a ("Staging: comedi: add usb dt9812 driver")
Cc: stable@xxxxxxxxxxxxxxx      # 2.6.29
Reviewed-by: Ian Abbott <abbotti@xxxxxxxxx>
Signed-off-by: Johan Hovold <johan@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20211027093529.30896-3-johan@xxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/staging/comedi/drivers/dt9812.c |  115 +++++++++++++++++++++++---------
 1 file changed, 86 insertions(+), 29 deletions(-)

--- a/drivers/staging/comedi/drivers/dt9812.c
+++ b/drivers/staging/comedi/drivers/dt9812.c
@@ -41,6 +41,7 @@
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/errno.h>
+#include <linux/slab.h>
 #include <linux/uaccess.h>
 
 #include "../comedi_usb.h"
@@ -246,22 +247,42 @@ static int dt9812_read_info(struct comed
 {
 	struct usb_device *usb = comedi_to_usb_dev(dev);
 	struct dt9812_private *devpriv = dev->private;
-	struct dt9812_usb_cmd cmd;
+	struct dt9812_usb_cmd *cmd;
+	size_t tbuf_size;
 	int count, ret;
+	void *tbuf;
 
-	cmd.cmd = cpu_to_le32(DT9812_R_FLASH_DATA);
-	cmd.u.flash_data_info.address =
+	tbuf_size = max(sizeof(*cmd), buf_size);
+
+	tbuf = kzalloc(tbuf_size, GFP_KERNEL);
+	if (!tbuf)
+		return -ENOMEM;
+
+	cmd = tbuf;
+
+	cmd->cmd = cpu_to_le32(DT9812_R_FLASH_DATA);
+	cmd->u.flash_data_info.address =
 	    cpu_to_le16(DT9812_DIAGS_BOARD_INFO_ADDR + offset);
-	cmd.u.flash_data_info.numbytes = cpu_to_le16(buf_size);
+	cmd->u.flash_data_info.numbytes = cpu_to_le16(buf_size);
 
 	/* DT9812 only responds to 32 byte writes!! */
 	ret = usb_bulk_msg(usb, usb_sndbulkpipe(usb, devpriv->cmd_wr.addr),
-			   &cmd, 32, &count, DT9812_USB_TIMEOUT);
+			   cmd, sizeof(*cmd), &count, DT9812_USB_TIMEOUT);
 	if (ret)
-		return ret;
+		goto out;
+
+	ret = usb_bulk_msg(usb, usb_rcvbulkpipe(usb, devpriv->cmd_rd.addr),
+			   tbuf, buf_size, &count, DT9812_USB_TIMEOUT);
+	if (!ret) {
+		if (count == buf_size)
+			memcpy(buf, tbuf, buf_size);
+		else
+			ret = -EREMOTEIO;
+	}
+out:
+	kfree(tbuf);
 
-	return usb_bulk_msg(usb, usb_rcvbulkpipe(usb, devpriv->cmd_rd.addr),
-			    buf, buf_size, &count, DT9812_USB_TIMEOUT);
+	return ret;
 }
 
 static int dt9812_read_multiple_registers(struct comedi_device *dev,
@@ -270,22 +291,42 @@ static int dt9812_read_multiple_register
 {
 	struct usb_device *usb = comedi_to_usb_dev(dev);
 	struct dt9812_private *devpriv = dev->private;
-	struct dt9812_usb_cmd cmd;
+	struct dt9812_usb_cmd *cmd;
 	int i, count, ret;
+	size_t buf_size;
+	void *buf;
+
+	buf_size = max_t(size_t, sizeof(*cmd), reg_count);
+
+	buf = kzalloc(buf_size, GFP_KERNEL);
+	if (!buf)
+		return -ENOMEM;
+
+	cmd = buf;
 
-	cmd.cmd = cpu_to_le32(DT9812_R_MULTI_BYTE_REG);
-	cmd.u.read_multi_info.count = reg_count;
+	cmd->cmd = cpu_to_le32(DT9812_R_MULTI_BYTE_REG);
+	cmd->u.read_multi_info.count = reg_count;
 	for (i = 0; i < reg_count; i++)
-		cmd.u.read_multi_info.address[i] = address[i];
+		cmd->u.read_multi_info.address[i] = address[i];
 
 	/* DT9812 only responds to 32 byte writes!! */
 	ret = usb_bulk_msg(usb, usb_sndbulkpipe(usb, devpriv->cmd_wr.addr),
-			   &cmd, 32, &count, DT9812_USB_TIMEOUT);
+			   cmd, sizeof(*cmd), &count, DT9812_USB_TIMEOUT);
 	if (ret)
-		return ret;
+		goto out;
 
-	return usb_bulk_msg(usb, usb_rcvbulkpipe(usb, devpriv->cmd_rd.addr),
-			    value, reg_count, &count, DT9812_USB_TIMEOUT);
+	ret = usb_bulk_msg(usb, usb_rcvbulkpipe(usb, devpriv->cmd_rd.addr),
+			   buf, reg_count, &count, DT9812_USB_TIMEOUT);
+	if (!ret) {
+		if (count == reg_count)
+			memcpy(value, buf, reg_count);
+		else
+			ret = -EREMOTEIO;
+	}
+out:
+	kfree(buf);
+
+	return ret;
 }
 
 static int dt9812_write_multiple_registers(struct comedi_device *dev,
@@ -294,19 +335,27 @@ static int dt9812_write_multiple_registe
 {
 	struct usb_device *usb = comedi_to_usb_dev(dev);
 	struct dt9812_private *devpriv = dev->private;
-	struct dt9812_usb_cmd cmd;
+	struct dt9812_usb_cmd *cmd;
 	int i, count;
+	int ret;
 
-	cmd.cmd = cpu_to_le32(DT9812_W_MULTI_BYTE_REG);
-	cmd.u.read_multi_info.count = reg_count;
+	cmd = kzalloc(sizeof(*cmd), GFP_KERNEL);
+	if (!cmd)
+		return -ENOMEM;
+
+	cmd->cmd = cpu_to_le32(DT9812_W_MULTI_BYTE_REG);
+	cmd->u.read_multi_info.count = reg_count;
 	for (i = 0; i < reg_count; i++) {
-		cmd.u.write_multi_info.write[i].address = address[i];
-		cmd.u.write_multi_info.write[i].value = value[i];
+		cmd->u.write_multi_info.write[i].address = address[i];
+		cmd->u.write_multi_info.write[i].value = value[i];
 	}
 
 	/* DT9812 only responds to 32 byte writes!! */
-	return usb_bulk_msg(usb, usb_sndbulkpipe(usb, devpriv->cmd_wr.addr),
-			    &cmd, 32, &count, DT9812_USB_TIMEOUT);
+	ret = usb_bulk_msg(usb, usb_sndbulkpipe(usb, devpriv->cmd_wr.addr),
+			   cmd, sizeof(*cmd), &count, DT9812_USB_TIMEOUT);
+	kfree(cmd);
+
+	return ret;
 }
 
 static int dt9812_rmw_multiple_registers(struct comedi_device *dev,
@@ -315,17 +364,25 @@ static int dt9812_rmw_multiple_registers
 {
 	struct usb_device *usb = comedi_to_usb_dev(dev);
 	struct dt9812_private *devpriv = dev->private;
-	struct dt9812_usb_cmd cmd;
+	struct dt9812_usb_cmd *cmd;
 	int i, count;
+	int ret;
+
+	cmd = kzalloc(sizeof(*cmd), GFP_KERNEL);
+	if (!cmd)
+		return -ENOMEM;
 
-	cmd.cmd = cpu_to_le32(DT9812_RMW_MULTI_BYTE_REG);
-	cmd.u.rmw_multi_info.count = reg_count;
+	cmd->cmd = cpu_to_le32(DT9812_RMW_MULTI_BYTE_REG);
+	cmd->u.rmw_multi_info.count = reg_count;
 	for (i = 0; i < reg_count; i++)
-		cmd.u.rmw_multi_info.rmw[i] = rmw[i];
+		cmd->u.rmw_multi_info.rmw[i] = rmw[i];
 
 	/* DT9812 only responds to 32 byte writes!! */
-	return usb_bulk_msg(usb, usb_sndbulkpipe(usb, devpriv->cmd_wr.addr),
-			    &cmd, 32, &count, DT9812_USB_TIMEOUT);
+	ret = usb_bulk_msg(usb, usb_sndbulkpipe(usb, devpriv->cmd_wr.addr),
+			   cmd, sizeof(*cmd), &count, DT9812_USB_TIMEOUT);
+	kfree(cmd);
+
+	return ret;
 }
 
 static int dt9812_digital_in(struct comedi_device *dev, u8 *bits)