From nobody Tue Oct 7 18:26:05 2025 Received: from smtp103.iad3a.emailsrvr.com (smtp103.iad3a.emailsrvr.com [173.203.187.103]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2E9041E2312 for ; Mon, 7 Jul 2025 15:41:47 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=173.203.187.103 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1751902910; cv=none; b=h2W/y6iu6DC61HEhR7lTNkFUkYhfY2U1f92eVTvqaTFmpcpvPEkdZRwaHZSG62PmgRl+NSQhxpPSGsQNE/5HnO2n91hfDWajT5Y8uaf1DNMna9aFBFim95z+eIW3fzgugl6EFpoq+Gnqz6ROcodsu4rS1jZkgqyov+ZjVA5EMlI= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1751902910; c=relaxed/simple; bh=FDDpW0WZ2LFiLbJb4SDzEsmW+vtcbA/gyC5BQi9dUwE=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=im0G0MUC5RGRksWGUM5BY33zuQU5EnGC7iFIiySUokIayKqfh+0YdRb2P+ZNWfLcplW9mW0g9aEk1hJrhqUX2RrTwZ0o8xAL0fFBWz9vdM5pxKawIkMQFNrINPRWUzCmsQx5x90DiVyzG9ADCEecgk61DPyXqD1+h3JW0DIXjMw= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=mev.co.uk; spf=pass smtp.mailfrom=mev.co.uk; dkim=pass (1024-bit key) header.d=mev.co.uk header.i=@mev.co.uk header.b=AEjLoP8Y; arc=none smtp.client-ip=173.203.187.103 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=mev.co.uk Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=mev.co.uk Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=mev.co.uk header.i=@mev.co.uk header.b="AEjLoP8Y" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=mev.co.uk; s=20221208-6x11dpa4; t=1751902445; bh=FDDpW0WZ2LFiLbJb4SDzEsmW+vtcbA/gyC5BQi9dUwE=; h=From:To:Subject:Date:From; b=AEjLoP8Yf23WBgsUK3eRysE19vpYr0MMTbY7oG95evb2GUyDfUoDA0GFVTbIoC6Nt sngvqIBiwcVvUCzSx+ahfPfnCoYSHLqsWM+lCVepc3shqilwsU4/lUI4JDlLpBWQvL Gt6qI4rL0O7HU1UjUJ4OYZXwu7HE3vZJuRJ9G884= X-Auth-ID: abbotti@mev.co.uk Received: by smtp21.relay.iad3a.emailsrvr.com (Authenticated sender: abbotti-AT-mev.co.uk) with ESMTPSA id 831C725201; Mon, 7 Jul 2025 11:34:04 -0400 (EDT) From: Ian Abbott To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , Ian Abbott , H Hartley Sweeten , syzbot+cb96ec476fb4914445c9@syzkaller.appspotmail.com, stable@vger.kernel.org Subject: [PATCH] comedi: Fix use of uninitialized data in insn_rw_emulate_bits() Date: Mon, 7 Jul 2025 16:33:54 +0100 Message-ID: <20250707153355.82474-1-abbotti@mev.co.uk> X-Mailer: git-send-email 2.47.2 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Classification-ID: 5fedf41f-a809-4e1b-bf14-73450e5f5c67-1-1 Content-Type: text/plain; charset="utf-8" For Comedi `INSN_READ` and `INSN_WRITE` instructions on "digital" subdevices (subdevice types `COMEDI_SUBD_DI`, `COMEDI_SUBD_DO`, and `COMEDI_SUBD_DIO`), it is common for the subdevice driver not to have `insn_read` and `insn_write` handler functions, but to have an `insn_bits` handler function for handling Comedi `INSN_BITS` instructions. In that case, the subdevice's `insn_read` and/or `insn_write` function handler pointers are set to point to the `insn_rw_emulate_bits()` function by `__comedi_device_postconfig()`. For `INSN_WRITE`, `insn_rw_emulate_bits()` currently assumes that the supplied `data[0]` value is a valid copy from user memory. It will at least exist because `do_insnlist_ioctl()` and `do_insn_ioctl()` in "comedi_fops.c" ensure at lease `MIN_SAMPLES` (16) elements are allocated. However, if `insn->n` is 0 (which is allowable for `INSN_READ` and `INSN_WRITE` instructions, then `data[0]` may contain uninitialized data, and certainly contains invalid data, possibly from a different instruction in the array of instructions handled by `do_insnlist_ioctl()`. This will result in an incorrect value being written to the digital output channel (or to the digital input/output channel if configured as an output), and may be reflected in the internal saved state of the channel. Fix it by returning 0 early if `insn->n` is 0, before reaching the code that accesses `data[0]`. Previously, the function always returned 1 on success, but it is supposed to be the number of data samples actually read or written up to `insn->n`, which is 0 in this case. Reported-by: syzbot+cb96ec476fb4914445c9@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=3Dcb96ec476fb4914445c9 Fixes: ed9eccbe8970 ("Staging: add comedi core") Cc: # 5.13+ Signed-off-by: Ian Abbott --- Patch does not apply cleanly to longterm kernels 5.4.x and 5.10.x. --- drivers/comedi/drivers.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/drivers/comedi/drivers.c b/drivers/comedi/drivers.c index 376130bfba8a..98e565088289 100644 --- a/drivers/comedi/drivers.c +++ b/drivers/comedi/drivers.c @@ -615,6 +615,9 @@ static int insn_rw_emulate_bits(struct comedi_device *d= ev, unsigned int _data[2]; int ret; =20 + if (insn->n =3D=3D 0) + return 0; + memset(_data, 0, sizeof(_data)); memset(&_insn, 0, sizeof(_insn)); _insn.insn =3D INSN_BITS; --=20 2.47.2