[PATCH] usb: ljca: bound bank_num in ljca_enumerate_gpio()

[Maoyi Xie <maoyixie.tju@gmail.com>]

ljca_enumerate_gpio() reads desc->bank_num from the device and loops
valid_pin[i] = get_unaligned_le32(...) for i < bank_num. valid_pin[]
holds only LJCA_MAX_GPIO_NUM / 32 = 2 entries.

Two checks run before the loop. The reply length must match
struct_size(desc, bank_desc, bank_num). The product
pins_per_bank * bank_num must not exceed LJCA_MAX_GPIO_NUM. Neither one
bounds bank_num against the size of valid_pin[]. The reply is capped at
LJCA_MAX_PAYLOAD_SIZE (60) bytes, so the struct_size check limits
bank_num to 9. A device that reports bank_num 9 with pins_per_bank 7
still passes both checks. gpio_num is 63 and the reply is 56 bytes. The
loop then writes nine u32 into the two entry array and overruns
valid_pin[] on the stack.

A broken or malicious LJCA device can therefore overflow the stack.
Reject a bank_num that does not fit valid_pin[].

Fixes: acd6199f195d ("usb: Add support for Intel LJCA device")
Cc: stable@vger.kernel.org
Signed-off-by: Maoyi Xie <maoyixie.tju@gmail.com>
---
 drivers/usb/misc/usb-ljca.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/usb/misc/usb-ljca.c b/drivers/usb/misc/usb-ljca.c
index c60121faa3da..a1876c05b7c2 100644
--- a/drivers/usb/misc/usb-ljca.c
+++ b/drivers/usb/misc/usb-ljca.c
@@ -596,6 +596,9 @@ static int ljca_enumerate_gpio(struct ljca_adapter *adap)
 	if (gpio_num > LJCA_MAX_GPIO_NUM)
 		return -EINVAL;
 
+	if (desc->bank_num > ARRAY_SIZE(valid_pin))
+		return -EINVAL;
+
 	/* construct platform data */
 	gpio_info = kzalloc_obj(*gpio_info);
 	if (!gpio_info)
-- 
2.34.1