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Date:   Tue, 24 Aug 2021 13:50:06 +0200
From:   Michal Kubecek <mkubecek@suse.cz>
To:     Alan Stern <stern@rowland.harvard.edu>
Cc:     syzbot <syzbot+9b57a46bf1801ce2a2ca@syzkaller.appspotmail.com>,
        benjamin.tissoires@redhat.com, jikos@kernel.org,
        linux-input@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-usb@vger.kernel.org, syzkaller-bugs@googlegroups.com
Subject: Re: [syzbot] WARNING in hid_submit_ctrl/usb_submit_urb
Message-ID: <20210824115006.a5zzgxjy6nwakdmg@lion.mk-sys.cz>
References: <20210819152626.GD228422@rowland.harvard.edu>
 <00000000000009e24705c9ecf9b3@google.com>
 <20210819195300.GA8613@rowland.harvard.edu>
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On Thu, Aug 19, 2021 at 03:53:00PM -0400, Alan Stern wrote:
> The following simplified variant of Michal's patch should fix the=20
> problem.
>=20
> Alan Stern
>=20
> #syz test: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux=
=2Egit 794c7931a242
>=20
> Index: usb-devel/drivers/hid/usbhid/hid-core.c
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
> --- usb-devel.orig/drivers/hid/usbhid/hid-core.c
> +++ usb-devel/drivers/hid/usbhid/hid-core.c
> @@ -377,27 +377,23 @@ static int hid_submit_ctrl(struct hid_de
>  	len =3D hid_report_len(report);
>  	if (dir =3D=3D USB_DIR_OUT) {
>  		usbhid->urbctrl->pipe =3D usb_sndctrlpipe(hid_to_usb_dev(hid), 0);
> -		usbhid->urbctrl->transfer_buffer_length =3D len;
>  		if (raw_report) {
>  			memcpy(usbhid->ctrlbuf, raw_report, len);
>  			kfree(raw_report);
>  			usbhid->ctrl[usbhid->ctrltail].raw_report =3D NULL;
>  		}
>  	} else {
> -		int maxpacket, padlen;
> +		int maxpacket;
> =20
>  		usbhid->urbctrl->pipe =3D usb_rcvctrlpipe(hid_to_usb_dev(hid), 0);
>  		maxpacket =3D usb_maxpacket(hid_to_usb_dev(hid),
>  					  usbhid->urbctrl->pipe, 0);
> -		if (maxpacket > 0) {
> -			padlen =3D DIV_ROUND_UP(len, maxpacket);
> -			padlen *=3D maxpacket;
> -			if (padlen > usbhid->bufsize)
> -				padlen =3D usbhid->bufsize;
> -		} else
> -			padlen =3D 0;
> -		usbhid->urbctrl->transfer_buffer_length =3D padlen;
> +		len +=3D (len =3D=3D 0);	/* Don't allow 0-length reports */
> +		len =3D round_up(len, maxpacket);
> +		if (len > usbhid->bufsize)
> +			len =3D usbhid->bufsize;
>  	}
> +	usbhid->urbctrl->transfer_buffer_length =3D len;
>  	usbhid->urbctrl->dev =3D hid_to_usb_dev(hid);
> =20
>  	usbhid->cr->bRequestType =3D USB_TYPE_CLASS | USB_RECIP_INTERFACE | dir;

I have also tested this patch on top of 5.14-rc7 on my system and it
does address the original issue (no error/warning messages in kernel log
and communication with the UPS works correctly). So if you are going to
submit the patch formally, feel free to use

Tested-by: Michal Kubecek <mkubecek@suse.cz>

Michal

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