Input: mms114 - reject an oversized device packet size

mms114_interrupt() reads a packet of touch data from the device into a
fixed-size on-stack buffer

	struct mms114_touch touch[MMS114_MAX_TOUCH];

which holds MMS114_MAX_TOUCH (10) events of MMS114_EVENT_SIZE (8) bytes,
i.e. 80 bytes. The length of the I2C read into it is taken verbatim from
the device:

	packet_size = mms114_read_reg(data, MMS114_PACKET_SIZE);
	if (packet_size <= 0)
		goto out;
	...
	error = __mms114_read_reg(data, MMS114_INFORMATION, packet_size,
			(u8 *)touch);

packet_size is a single device register byte (0x0F) and the only check
is the lower bound packet_size <= 0; it is never bounded against the
size of touch[]. A malfunctioning, malicious or counterfeit controller
(or an attacker tampering with the I2C bus) can report a packet_size of
up to 255, so __mms114_read_reg() writes up to 175 bytes past the end of
touch[] on the IRQ-thread stack: a stack out-of-bounds write that can
overwrite the stack canary, saved registers and the return address.

A well-formed device never reports more than the buffer holds, so reject
an oversized packet and drop the report, consistent with the handler's
other error paths, rather than reading past the buffer.

Fixes: 07b8481d4aff ("Input: add MELFAS mms114 touchscreen driver")
Signed-off-by: Bryam Vargas <hexlabsecurity@proton.me>
Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260612-b4-disp-dc4b8dc4-v1-1-d7cb0a828d92@proton.me
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

diff --git a/drivers/input/touchscreen/mms114.c b/drivers/input/touchscreen/mms114.c
index 9597214d9d3c9db47e9b00a799f6495ed6ae235e..4d748a13408d1deffca95230ba43fdf6d9779bf7 100644 (file)
--- a/drivers/input/touchscreen/mms114.c
+++ b/drivers/input/touchscreen/mms114.c
@@ -226,6 +226,12 @@ static irqreturn_t mms114_interrupt(int irq, void *dev_id)
        if (packet_size <= 0)
                goto out;
 
+       if (packet_size > sizeof(touch)) {
+               dev_err(&client->dev, "Invalid packet size %d (max %zu)\n",
+                       packet_size, sizeof(touch));
+               goto out;
+       }
+
        /* MMS136 has slightly different event size */
        if (data->type == TYPE_MMS134S || data->type == TYPE_MMS136)
                touch_size = packet_size / MMS136_EVENT_SIZE;