linux-kernel - [PATCH 3.16 172/212] ALSA: timer: Reject user params with too small ticks

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Message-ID: <lsq.1496331796.921562048@decadent.org.uk>
Date:   Thu, 01 Jun 2017 16:43:16 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Dmitry Vyukov" <dvyukov@...gle.com>,
        "Takashi Iwai" <tiwai@...e.de>
Subject: [PATCH 3.16 172/212] ALSA: timer: Reject user params with too
 small ticks

3.16.44-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Takashi Iwai <tiwai@...e.de>

commit 71321eb3f2d0df4e6c327e0b936eec4458a12054 upstream.

When a user sets a too small ticks with a fine-grained timer like
hrtimer, the kernel tries to fire up the timer irq too frequently.
This may lead to the condensed locks, eventually the kernel spinlock
lockup with warnings.

For avoiding such a situation, we define a lower limit of the
resolution, namely 1ms.  When the user passes a too small tick value
that results in less than that, the kernel returns -EINVAL now.

Reported-by: Dmitry Vyukov <dvyukov@...gle.com>
Signed-off-by: Takashi Iwai <tiwai@...e.de>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 sound/core/timer.c | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

--- a/sound/core/timer.c
+++ b/sound/core/timer.c
@@ -1715,9 +1715,21 @@ static int snd_timer_user_params(struct
 		return -EBADFD;
 	if (copy_from_user(&params, _params, sizeof(params)))
 		return -EFAULT;
-	if (!(t->hw.flags & SNDRV_TIMER_HW_SLAVE) && params.ticks < 1) {
-		err = -EINVAL;
-		goto _end;
+	if (!(t->hw.flags & SNDRV_TIMER_HW_SLAVE)) {
+		u64 resolution;
+
+		if (params.ticks < 1) {
+			err = -EINVAL;
+			goto _end;
+		}
+
+		/* Don't allow resolution less than 1ms */
+		resolution = snd_timer_resolution(tu->timeri);
+		resolution *= params.ticks;
+		if (resolution < 1000000) {
+			err = -EINVAL;
+			goto _end;
+		}
 	}
 	if (params.queue_size > 0 &&
 	    (params.queue_size < 32 || params.queue_size > 1024)) {