[PATCH 5.4.y 3/3] Input: pegasus-notetaker - fix potential out-of-bounds access

[Sasha Levin <sashal@kernel.org>]

From: Seungjin Bae <eeodqql09@gmail.com>

[ Upstream commit 69aeb507312306f73495598a055293fa749d454e ]

In the pegasus_notetaker driver, the pegasus_probe() function allocates
the URB transfer buffer using the wMaxPacketSize value from
the endpoint descriptor. An attacker can use a malicious USB descriptor
to force the allocation of a very small buffer.

Subsequently, if the device sends an interrupt packet with a specific
pattern (e.g., where the first byte is 0x80 or 0x42),
the pegasus_parse_packet() function parses the packet without checking
the allocated buffer size. This leads to an out-of-bounds memory access.

Fixes: 1afca2b66aac ("Input: add Pegasus Notetaker tablet driver")
Signed-off-by: Seungjin Bae <eeodqql09@gmail.com>
Link: https://lore.kernel.org/r/20251007214131.3737115-2-eeodqql09@gmail.com
Cc: stable@vger.kernel.org
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/input/tablet/pegasus_notetaker.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/input/tablet/pegasus_notetaker.c b/drivers/input/tablet/pegasus_notetaker.c
index 4e412a73a5aad..64a5ce5462293 100644
--- a/drivers/input/tablet/pegasus_notetaker.c
+++ b/drivers/input/tablet/pegasus_notetaker.c
@@ -63,6 +63,9 @@
 #define BUTTON_PRESSED			0xb5
 #define COMMAND_VERSION			0xa9
 
+/* 1 Status + 1 Color + 2 X + 2 Y = 6 bytes */
+#define NOTETAKER_PACKET_SIZE		6
+
 /* in xy data packet */
 #define BATTERY_NO_REPORT		0x40
 #define BATTERY_LOW			0x41
@@ -297,6 +300,12 @@ static int pegasus_probe(struct usb_interface *intf,
 
 	pipe = usb_rcvintpipe(dev, endpoint->bEndpointAddress);
 	pegasus->data_len = usb_maxpacket(dev, pipe);
+	if (pegasus->data_len < NOTETAKER_PACKET_SIZE) {
+		dev_err(&intf->dev, "packet size is too small (%d)\n",
+			pegasus->data_len);
+		error = -EINVAL;
+		goto err_free_mem;
+	}
 
 	pegasus->data = usb_alloc_coherent(dev, pegasus->data_len, GFP_KERNEL,
 					   &pegasus->data_dma);
-- 
2.51.0