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Message-ID: <lsq.1456263723.654953452@decadent.org.uk>
Date: Tue, 23 Feb 2016 21:42:03 +0000
From: Ben Hutchings <ben@...adent.org.uk>
To: linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC: akpm@...ux-foundation.org, "Takashi Iwai" <tiwai@...e.de>
Subject: [PATCH 3.2 57/67] ALSA: timer: Fix race at concurrent reads
3.2.78-rc1 review patch. If anyone has any objections, please let me know.
------------------
From: Takashi Iwai <tiwai@...e.de>
commit 4dff5c7b7093b19c19d3a100f8a3ad87cb7cd9e7 upstream.
snd_timer_user_read() has a potential race among parallel reads, as
qhead and qused are updated outside the critical section due to
copy_to_user() calls. Move them into the critical section, and also
sanitize the relevant code a bit.
Signed-off-by: Takashi Iwai <tiwai@...e.de>
[bwh: Backported to 3.2: there's no check for tu->connected to fix up]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
--- a/sound/core/timer.c
+++ b/sound/core/timer.c
@@ -1890,6 +1890,7 @@ static ssize_t snd_timer_user_read(struc
{
struct snd_timer_user *tu;
long result = 0, unit;
+ int qhead;
int err = 0;
tu = file->private_data;
@@ -1901,7 +1902,7 @@ static ssize_t snd_timer_user_read(struc
if ((file->f_flags & O_NONBLOCK) != 0 || result > 0) {
err = -EAGAIN;
- break;
+ goto _error;
}
set_current_state(TASK_INTERRUPTIBLE);
@@ -1916,38 +1917,33 @@ static ssize_t snd_timer_user_read(struc
if (signal_pending(current)) {
err = -ERESTARTSYS;
- break;
+ goto _error;
}
}
+ qhead = tu->qhead++;
+ tu->qhead %= tu->queue_size;
spin_unlock_irq(&tu->qlock);
- if (err < 0)
- goto _error;
if (tu->tread) {
- if (copy_to_user(buffer, &tu->tqueue[tu->qhead++],
- sizeof(struct snd_timer_tread))) {
+ if (copy_to_user(buffer, &tu->tqueue[qhead],
+ sizeof(struct snd_timer_tread)))
err = -EFAULT;
- goto _error;
- }
} else {
- if (copy_to_user(buffer, &tu->queue[tu->qhead++],
- sizeof(struct snd_timer_read))) {
+ if (copy_to_user(buffer, &tu->queue[qhead],
+ sizeof(struct snd_timer_read)))
err = -EFAULT;
- goto _error;
- }
}
- tu->qhead %= tu->queue_size;
-
- result += unit;
- buffer += unit;
-
spin_lock_irq(&tu->qlock);
tu->qused--;
+ if (err < 0)
+ goto _error;
+ result += unit;
+ buffer += unit;
}
- spin_unlock_irq(&tu->qlock);
_error:
+ spin_unlock_irq(&tu->qlock);
return result > 0 ? result : err;
}
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