[PATCH] USB: serial: io_ti: reject oversized boot-mode firmware images

[Pengpeng Hou]

do_boot_mode() allocates a fixed 15.5 KiB staging buffer plus the I2C
image header and then copies fw->size - 4 bytes into it.
check_fw_sanity() validates the firmware's internal record accounting,
but the boot-mode copy still needs to prove that the raw firmware
payload fits in the fixed staging buffer.

Reject firmware images that are shorter than the skipped 4-byte prefix
or whose remaining payload exceeds the staging buffer before copying the
data.

Signed-off-by: Pengpeng Hou <pengpeng@xxxxxxxxxxx>
---
 drivers/usb/serial/io_ti.c |    6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/usb/serial/io_ti.c b/drivers/usb/serial/io_ti.c
index d48819d7..3bdcbd6f 100644
--- a/drivers/usb/serial/io_ti.c
+++ b/drivers/usb/serial/io_ti.c
@@ -1466,6 +1466,12 @@ static int do_boot_mode(struct edgeport_serial *serial,
 		/* Allocate a 15.5k buffer + 3 byte header */
 		buffer_size = (((1024 * 16) - 512) +
 					sizeof(struct ti_i2c_image_header));
+		if (fw->size < 4 || fw->size - 4 > buffer_size) {
+			dev_err(dev, "%s - firmware image is too large\n",
+				__func__);
+			return -EINVAL;
+		}
+
 		buffer = kmalloc(buffer_size, GFP_KERNEL);
 		if (!buffer)
 			return -ENOMEM;