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[ALSA] Fix races in PCM OSS emulation
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Fixed the race among multiple threads accessing the OSS PCM
instance concurrently by simply introducing a mutex for protecting
a setup of the PCM.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>
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Takashi Iwai authored and Jaroslav Kysela committed Dec 20, 2006
1 parent ba8bdf8 commit e3a5d59
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Showing 2 changed files with 41 additions and 12 deletions.
1 change: 1 addition & 0 deletions include/sound/pcm_oss.h
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Original file line number Diff line number Diff line change
Expand Up @@ -56,6 +56,7 @@ struct snd_pcm_oss_runtime {
size_t mmap_bytes;
char *buffer; /* vmallocated period */
size_t buffer_used; /* used length from period buffer */
struct mutex params_lock;
#ifdef CONFIG_SND_PCM_OSS_PLUGINS
struct snd_pcm_plugin *plugin_first;
struct snd_pcm_plugin *plugin_last;
Expand Down
52 changes: 40 additions & 12 deletions sound/core/oss/pcm_oss.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -810,6 +810,8 @@ static int snd_pcm_oss_change_params(struct snd_pcm_substream *substream)
struct snd_mask sformat_mask;
struct snd_mask mask;

if (mutex_lock_interruptible(&runtime->oss.params_lock))
return -EINTR;
sw_params = kmalloc(sizeof(*sw_params), GFP_KERNEL);
params = kmalloc(sizeof(*params), GFP_KERNEL);
sparams = kmalloc(sizeof(*sparams), GFP_KERNEL);
Expand Down Expand Up @@ -1020,6 +1022,7 @@ static int snd_pcm_oss_change_params(struct snd_pcm_substream *substream)
kfree(sw_params);
kfree(params);
kfree(sparams);
mutex_unlock(&runtime->oss.params_lock);
return err;
}

Expand Down Expand Up @@ -1307,14 +1310,17 @@ static ssize_t snd_pcm_oss_write1(struct snd_pcm_substream *substream, const cha

if ((tmp = snd_pcm_oss_make_ready(substream)) < 0)
return tmp;
mutex_lock(&runtime->oss.params_lock);
while (bytes > 0) {
if (bytes < runtime->oss.period_bytes || runtime->oss.buffer_used > 0) {
tmp = bytes;
if (tmp + runtime->oss.buffer_used > runtime->oss.period_bytes)
tmp = runtime->oss.period_bytes - runtime->oss.buffer_used;
if (tmp > 0) {
if (copy_from_user(runtime->oss.buffer + runtime->oss.buffer_used, buf, tmp))
return xfer > 0 ? (snd_pcm_sframes_t)xfer : -EFAULT;
if (copy_from_user(runtime->oss.buffer + runtime->oss.buffer_used, buf, tmp)) {
tmp = -EFAULT;
goto err;
}
}
runtime->oss.buffer_used += tmp;
buf += tmp;
Expand All @@ -1325,22 +1331,24 @@ static ssize_t snd_pcm_oss_write1(struct snd_pcm_substream *substream, const cha
tmp = snd_pcm_oss_write2(substream, runtime->oss.buffer + runtime->oss.period_ptr,
runtime->oss.buffer_used - runtime->oss.period_ptr, 1);
if (tmp <= 0)
return xfer > 0 ? (snd_pcm_sframes_t)xfer : tmp;
goto err;
runtime->oss.bytes += tmp;
runtime->oss.period_ptr += tmp;
runtime->oss.period_ptr %= runtime->oss.period_bytes;
if (runtime->oss.period_ptr == 0 ||
runtime->oss.period_ptr == runtime->oss.buffer_used)
runtime->oss.buffer_used = 0;
else if ((substream->f_flags & O_NONBLOCK) != 0)
return xfer > 0 ? xfer : -EAGAIN;
else if ((substream->f_flags & O_NONBLOCK) != 0) {
tmp = -EAGAIN;
goto err;
}
}
} else {
tmp = snd_pcm_oss_write2(substream,
(const char __force *)buf,
runtime->oss.period_bytes, 0);
if (tmp <= 0)
return xfer > 0 ? (snd_pcm_sframes_t)xfer : tmp;
goto err;
runtime->oss.bytes += tmp;
buf += tmp;
bytes -= tmp;
Expand All @@ -1350,7 +1358,12 @@ static ssize_t snd_pcm_oss_write1(struct snd_pcm_substream *substream, const cha
break;
}
}
mutex_unlock(&runtime->oss.params_lock);
return xfer;

err:
mutex_unlock(&runtime->oss.params_lock);
return xfer > 0 ? (snd_pcm_sframes_t)xfer : tmp;
}

static ssize_t snd_pcm_oss_read2(struct snd_pcm_substream *substream, char *buf, size_t bytes, int in_kernel)
Expand Down Expand Up @@ -1397,21 +1410,24 @@ static ssize_t snd_pcm_oss_read1(struct snd_pcm_substream *substream, char __use

if ((tmp = snd_pcm_oss_make_ready(substream)) < 0)
return tmp;
mutex_lock(&runtime->oss.params_lock);
while (bytes > 0) {
if (bytes < runtime->oss.period_bytes || runtime->oss.buffer_used > 0) {
if (runtime->oss.buffer_used == 0) {
tmp = snd_pcm_oss_read2(substream, runtime->oss.buffer, runtime->oss.period_bytes, 1);
if (tmp <= 0)
return xfer > 0 ? (snd_pcm_sframes_t)xfer : tmp;
goto err;
runtime->oss.bytes += tmp;
runtime->oss.period_ptr = tmp;
runtime->oss.buffer_used = tmp;
}
tmp = bytes;
if ((size_t) tmp > runtime->oss.buffer_used)
tmp = runtime->oss.buffer_used;
if (copy_to_user(buf, runtime->oss.buffer + (runtime->oss.period_ptr - runtime->oss.buffer_used), tmp))
return xfer > 0 ? (snd_pcm_sframes_t)xfer : -EFAULT;
if (copy_to_user(buf, runtime->oss.buffer + (runtime->oss.period_ptr - runtime->oss.buffer_used), tmp)) {
tmp = -EFAULT;
goto err;
}
buf += tmp;
bytes -= tmp;
xfer += tmp;
Expand All @@ -1420,14 +1436,19 @@ static ssize_t snd_pcm_oss_read1(struct snd_pcm_substream *substream, char __use
tmp = snd_pcm_oss_read2(substream, (char __force *)buf,
runtime->oss.period_bytes, 0);
if (tmp <= 0)
return xfer > 0 ? (snd_pcm_sframes_t)xfer : tmp;
goto err;
runtime->oss.bytes += tmp;
buf += tmp;
bytes -= tmp;
xfer += tmp;
}
}
mutex_unlock(&runtime->oss.params_lock);
return xfer;

err:
mutex_unlock(&runtime->oss.params_lock);
return xfer > 0 ? (snd_pcm_sframes_t)xfer : tmp;
}

static int snd_pcm_oss_reset(struct snd_pcm_oss_file *pcm_oss_file)
Expand Down Expand Up @@ -1528,6 +1549,7 @@ static int snd_pcm_oss_sync(struct snd_pcm_oss_file *pcm_oss_file)
return err;
format = snd_pcm_oss_format_from(runtime->oss.format);
width = snd_pcm_format_physical_width(format);
mutex_lock(&runtime->oss.params_lock);
if (runtime->oss.buffer_used > 0) {
#ifdef OSS_DEBUG
printk("sync: buffer_used\n");
Expand All @@ -1537,8 +1559,10 @@ static int snd_pcm_oss_sync(struct snd_pcm_oss_file *pcm_oss_file)
runtime->oss.buffer + runtime->oss.buffer_used,
size);
err = snd_pcm_oss_sync1(substream, runtime->oss.period_bytes);
if (err < 0)
if (err < 0) {
mutex_unlock(&runtime->oss.params_lock);
return err;
}
} else if (runtime->oss.period_ptr > 0) {
#ifdef OSS_DEBUG
printk("sync: period_ptr\n");
Expand All @@ -1548,8 +1572,10 @@ static int snd_pcm_oss_sync(struct snd_pcm_oss_file *pcm_oss_file)
runtime->oss.buffer,
size * 8 / width);
err = snd_pcm_oss_sync1(substream, size);
if (err < 0)
if (err < 0) {
mutex_unlock(&runtime->oss.params_lock);
return err;
}
}
/*
* The ALSA's period might be a bit large than OSS one.
Expand Down Expand Up @@ -1579,6 +1605,7 @@ static int snd_pcm_oss_sync(struct snd_pcm_oss_file *pcm_oss_file)
snd_pcm_lib_writev(substream, buffers, size);
}
}
mutex_unlock(&runtime->oss.params_lock);
/*
* finish sync: drain the buffer
*/
Expand Down Expand Up @@ -2172,6 +2199,7 @@ static void snd_pcm_oss_init_substream(struct snd_pcm_substream *substream,
runtime->oss.params = 1;
runtime->oss.trigger = 1;
runtime->oss.rate = 8000;
mutex_init(&runtime->oss.params_lock);
switch (SNDRV_MINOR_OSS_DEVICE(minor)) {
case SNDRV_MINOR_OSS_PCM_8:
runtime->oss.format = AFMT_U8;
Expand Down

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