[alsa-devel] [PATCH] ALSA: msnd: Optimize / harden DSP and MIDI loops

[grygorii tertychnyi]

From: Takashi Iwai <tiwai at suse.de>

commit 20e2b791796bd68816fa115f12be5320de2b8021 upstream.

The ISA msnd drivers have loops fetching the ring-buffer head, tail
and size values inside the loops.  Such codes are inefficient and
fragile.

This patch optimizes it, and also adds the sanity check to avoid the
endless loops.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=196131
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=196133
Signed-off-by: Takashi Iwai <tiwai at suse.de>
Cc: xe-linux-external at cisco.com
Signed-off-by: grygorii tertychnyi <gtertych at cisco.com>
---
 sound/isa/msnd/msnd_midi.c     | 30 +++++++++++++++---------------
 sound/isa/msnd/msnd_pinnacle.c | 23 ++++++++++++-----------
 2 files changed, 27 insertions(+), 26 deletions(-)

diff --git a/sound/isa/msnd/msnd_midi.c b/sound/isa/msnd/msnd_midi.c
index ffc67fd80c23..58e59cd3c95c 100644
--- a/sound/isa/msnd/msnd_midi.c
+++ b/sound/isa/msnd/msnd_midi.c
@@ -120,24 +120,24 @@ void snd_msndmidi_input_read(void *mpuv)
 	unsigned long flags;
 	struct snd_msndmidi *mpu = mpuv;
 	void *pwMIDQData = mpu->dev->mappedbase + MIDQ_DATA_BUFF;
+	u16 head, tail, size;
 
 	spin_lock_irqsave(&mpu->input_lock, flags);
-	while (readw(mpu->dev->MIDQ + JQS_wTail) !=
-	       readw(mpu->dev->MIDQ + JQS_wHead)) {
-		u16 wTmp, val;
-		val = readw(pwMIDQData + 2 * readw(mpu->dev->MIDQ + JQS_wHead));
-
-			if (test_bit(MSNDMIDI_MODE_BIT_INPUT_TRIGGER,
-				     &mpu->mode))
-				snd_rawmidi_receive(mpu->substream_input,
-						    (unsigned char *)&val, 1);
-
-		wTmp = readw(mpu->dev->MIDQ + JQS_wHead) + 1;
-		if (wTmp > readw(mpu->dev->MIDQ + JQS_wSize))
-			writew(0,  mpu->dev->MIDQ + JQS_wHead);
-		else
-			writew(wTmp,  mpu->dev->MIDQ + JQS_wHead);
+	head = readw(mpu->dev->MIDQ + JQS_wHead);
+	tail = readw(mpu->dev->MIDQ + JQS_wTail);
+	size = readw(mpu->dev->MIDQ + JQS_wSize);
+	if (head > size || tail > size)
+		goto out;
+	while (head != tail) {
+		unsigned char val = readw(pwMIDQData + 2 * head);
+
+		if (test_bit(MSNDMIDI_MODE_BIT_INPUT_TRIGGER, &mpu->mode))
+			snd_rawmidi_receive(mpu->substream_input, &val, 1);
+		if (++head > size)
+			head = 0;
+		writew(head, mpu->dev->MIDQ + JQS_wHead);
 	}
+ out:
 	spin_unlock_irqrestore(&mpu->input_lock, flags);
 }
 EXPORT_SYMBOL(snd_msndmidi_input_read);
diff --git a/sound/isa/msnd/msnd_pinnacle.c b/sound/isa/msnd/msnd_pinnacle.c
index 4c072666115d..a31ea6c22d19 100644
--- a/sound/isa/msnd/msnd_pinnacle.c
+++ b/sound/isa/msnd/msnd_pinnacle.c
@@ -170,23 +170,24 @@ static irqreturn_t snd_msnd_interrupt(int irq, void *dev_id)
 {
 	struct snd_msnd *chip = dev_id;
 	void *pwDSPQData = chip->mappedbase + DSPQ_DATA_BUFF;
+	u16 head, tail, size;
 
 	/* Send ack to DSP */
 	/* inb(chip->io + HP_RXL); */
 
 	/* Evaluate queued DSP messages */
-	while (readw(chip->DSPQ + JQS_wTail) != readw(chip->DSPQ + JQS_wHead)) {
-		u16 wTmp;
-
-		snd_msnd_eval_dsp_msg(chip,
-			readw(pwDSPQData + 2 * readw(chip->DSPQ + JQS_wHead)));
-
-		wTmp = readw(chip->DSPQ + JQS_wHead) + 1;
-		if (wTmp > readw(chip->DSPQ + JQS_wSize))
-			writew(0, chip->DSPQ + JQS_wHead);
-		else
-			writew(wTmp, chip->DSPQ + JQS_wHead);
+	head = readw(chip->DSPQ + JQS_wHead);
+	tail = readw(chip->DSPQ + JQS_wTail);
+	size = readw(chip->DSPQ + JQS_wSize);
+	if (head > size || tail > size)
+		goto out;
+	while (head != tail) {
+		snd_msnd_eval_dsp_msg(chip, readw(pwDSPQData + 2 * head));
+		if (++head > size)
+			head = 0;
+		writew(head, chip->DSPQ + JQS_wHead);
 	}
+ out:
 	/* Send ack to DSP */
 	inb(chip->io + HP_RXL);
 	return IRQ_HANDLED;
-- 
2.10.3.dirty