linux-kernel - [PATCH] firmware: cs_dsp: Don't allow writes to read-only controls

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Message-ID: <20240702110809.16836-1-rf@opensource.cirrus.com>
Date: Tue, 2 Jul 2024 12:08:09 +0100
From: Richard Fitzgerald <rf@...nsource.cirrus.com>
To: <broonie@...nel.org>
CC: <alsa-devel@...a-project.org>, <linux-sound@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <patches@...nsource.cirrus.com>,
        "Richard
 Fitzgerald" <rf@...nsource.cirrus.com>
Subject: [PATCH] firmware: cs_dsp: Don't allow writes to read-only controls

Add a check to cs_dsp_coeff_write_ctrl() to abort if the control
is not writeable.

The cs_dsp code originated as an ASoC driver (wm_adsp) where all
controls were exported as ALSA controls. It relied on ALSA to
enforce the read-only permission. Now that the code has been
separated from ALSA/ASoC it must perform its own permission check.

This isn't currently causing any problems so there shouldn't be any
need to backport this. If the client of cs_dsp exposes the control as
an ALSA control, it should set permissions on that ALSA control to
protect it. The few uses of cs_dsp_coeff_write_ctrl() inside drivers
are for writable controls.

Signed-off-by: Richard Fitzgerald <rf@...nsource.cirrus.com>
---
 drivers/firmware/cirrus/cs_dsp.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/firmware/cirrus/cs_dsp.c b/drivers/firmware/cirrus/cs_dsp.c
index 16484ab9b09d..be8747d227db 100644
--- a/drivers/firmware/cirrus/cs_dsp.c
+++ b/drivers/firmware/cirrus/cs_dsp.c
@@ -796,6 +796,9 @@ int cs_dsp_coeff_write_ctrl(struct cs_dsp_coeff_ctl *ctl,

 	lockdep_assert_held(&ctl->dsp->pwr_lock);

+	if (ctl->flags && !(ctl->flags & WMFW_CTL_FLAG_WRITEABLE))
+		return -EPERM;
+
 	if (len + off * sizeof(u32) > ctl->len)
 		return -EINVAL;

-- 
2.39.2