linux-kernel - Re: [PATCH] usb: r8a66597-hcd: fix potential divide-by-zero in prepare_packet

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Message-ID: <2026011022-cosmos-consult-4c50@gregkh>
Date: Sat, 10 Jan 2026 21:02:40 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: pip-izony <eeodqql09@...il.com>
Cc: Ingo Molnar <mingo@...nel.org>, Thomas Gleixner <tglx@...utronix.de>,
	Kyungtae Kim <Kyungtae.Kim@...tmouth.edu>,
	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] usb: r8a66597-hcd: fix potential divide-by-zero in
 prepare_packet_read()

On Sat, Jan 10, 2026 at 02:22:33PM -0500, pip-izony wrote:
> From: Seungjin Bae <eeodqql09@...il.com>
> 
> The `prepare_packet_read()` function calculates the number of packets
> required for a transfer by dividing the transfer buffer length by the
> maximum packet size (`td->maxpacket`). The `td->maxpacket` is
> initialized in `r8a66597_make_td()` function based on the endpoint
> descriptor. However, it does not validate whether `td->maxpacket` is
> zero before using it in the `DIV_ROUND_UP` macro.
> 
> If a malicious USB device sends a descriptor with `wMaxPacketSize` set to
> 0, it triggers a divide-by-zero exception (kernel panic).

Same here, when can this happen, before a device is bound to the device
or afterward?

thanks,

greg k-h