[PATCH 3.16 054/366] ALSA: pcm: Return -EBUSY for OSS ioctls changing busy streams

Ben Hutchings
2018-10-14T23:20:48Z

From: Takashi Iwai <tiwai@suse.de>

commit 40cab6e88cb0b6c56d3f30b7491a20e803f948f6 upstream.

OSS PCM stream management isn't modal but it allows ioctls issued at
any time for changing the parameters. In the previous hardening
patch ("ALSA: pcm: Avoid potential races between OSS ioctls and
read/write"), we covered these races and prevent the corruption by
protecting the concurrent accesses via params_lock mutex. However,
this means that some ioctls that try to change the stream parameter
(e.g. channels or format) would be blocked until the read/write
finishes, and it may take really long.

Basically changing the parameter while reading/writing is an invalid
operation, hence it's even more user-friendly from the API POV if it
returns -EBUSY in such a situation.

This patch adds such checks in the relevant ioctls with the addition
of read/write access refcount.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
include/sound/pcm_oss.h | 1 +
sound/core/oss/pcm_oss.c | 36 +++++++++++++++++++++++++++---------
2 files changed, 28 insertions(+), 9 deletions(-)

--- a/include/sound/pcm_oss.h
+++ b/include/sound/pcm_oss.h
@@ -57,6 +57,7 @@ struct snd_pcm_oss_runtime {
char *buffer; /* vmallocated period */
size_t buffer_used; /* used length from period buffer */
struct mutex params_lock;
+ atomic_t rw_ref; /* concurrent read/write accesses */
#ifdef CONFIG_SND_PCM_OSS_PLUGINS
struct snd_pcm_plugin *plugin_first;
struct snd_pcm_plugin *plugin_last;
--- a/sound/core/oss/pcm_oss.c
+++ b/sound/core/oss/pcm_oss.c
@@ -1406,6 +1406,7 @@ static ssize_t snd_pcm_oss_write1(struct
if (atomic_read(&substream->mmap_count))
return -ENXIO;

+ atomic_inc(&runtime->oss.rw_ref);
while (bytes > 0) {
if (mutex_lock_interruptible(&runtime->oss.params_lock)) {
tmp = -ERESTARTSYS;
@@ -1469,6 +1470,7 @@ static ssize_t snd_pcm_oss_write1(struct
}
tmp = 0;
}
+ atomic_dec(&runtime->oss.rw_ref);
return xfer > 0 ? (snd_pcm_sframes_t)xfer : tmp;
}

@@ -1514,6 +1516,7 @@ static ssize_t snd_pcm_oss_read1(struct
if (atomic_read(&substream->mmap_count))
return -ENXIO;

+ atomic_inc(&runtime->oss.rw_ref);
while (bytes > 0) {
if (mutex_lock_interruptible(&runtime->oss.params_lock)) {
tmp = -ERESTARTSYS;
@@ -1562,6 +1565,7 @@ static ssize_t snd_pcm_oss_read1(struct
}
tmp = 0;
}
+ atomic_dec(&runtime->oss.rw_ref);
return xfer > 0 ? (snd_pcm_sframes_t)xfer : tmp;
}

@@ -1668,8 +1672,11 @@ static int snd_pcm_oss_sync(struct snd_p
goto __direct;
if ((err = snd_pcm_oss_make_ready(substream)) < 0)
return err;
- if (mutex_lock_interruptible(&runtime->oss.params_lock))
+ atomic_inc(&runtime->oss.rw_ref);
+ if (mutex_lock_interruptible(&runtime->oss.params_lock)) {
+ atomic_dec(&runtime->oss.rw_ref);
return -ERESTARTSYS;
+ }
format = snd_pcm_oss_format_from(runtime->oss.format);
width = snd_pcm_format_physical_width(format);
if (runtime->oss.buffer_used > 0) {
@@ -1681,10 +1688,8 @@ static int snd_pcm_oss_sync(struct snd_p
runtime->oss.buffer + runtime->oss.buffer_used,
size);
err = snd_pcm_oss_sync1(substream, runtime->oss.period_bytes);
- if (err < 0) {
- mutex_unlock(&runtime->oss.params_lock);
- return err;
- }
+ if (err < 0)
+ goto unlock;
} else if (runtime->oss.period_ptr > 0) {
#ifdef OSS_DEBUG
pcm_dbg(substream->pcm, "sync: period_ptr\n");
@@ -1694,10 +1699,8 @@ static int snd_pcm_oss_sync(struct snd_p
runtime->oss.buffer,
size * 8 / width);
err = snd_pcm_oss_sync1(substream, size);
- if (err < 0) {
- mutex_unlock(&runtime->oss.params_lock);
- return err;
- }
+ if (err < 0)
+ goto unlock;
}
/*
* The ALSA's period might be a bit large than OSS one.
@@ -1728,7 +1731,11 @@ static int snd_pcm_oss_sync(struct snd_p
snd_pcm_lib_writev(substream, buffers, size);
}
}
+unlock:
mutex_unlock(&runtime->oss.params_lock);
+ atomic_dec(&runtime->oss.rw_ref);
+ if (err < 0)
+ return err;
/*
* finish sync: drain the buffer
*/
@@ -1776,6 +1783,8 @@ static int snd_pcm_oss_set_rate(struct s
rate = 192000;
if (mutex_lock_interruptible(&runtime->oss.params_lock))
return -ERESTARTSYS;
+ if (atomic_read(&runtime->oss.rw_ref))
+ return -EBUSY;
if (runtime->oss.rate != rate) {
runtime->oss.params = 1;
runtime->oss.rate = rate;
@@ -1810,6 +1819,8 @@ static int snd_pcm_oss_set_channels(stru
runtime = substream->runtime;
if (mutex_lock_interruptible(&runtime->oss.params_lock))
return -ERESTARTSYS;
+ if (atomic_read(&runtime->oss.rw_ref))
+ return -EBUSY;
if (runtime->oss.channels != channels) {
runtime->oss.params = 1;
runtime->oss.channels = channels;
@@ -1898,6 +1909,8 @@ static int snd_pcm_oss_set_format(struct
if (substream == NULL)
continue;
runtime = substream->runtime;
+ if (atomic_read(&runtime->oss.rw_ref))
+ return -EBUSY;
if (mutex_lock_interruptible(&runtime->oss.params_lock))
return -ERESTARTSYS;
if (runtime->oss.format != format) {
@@ -1952,6 +1965,8 @@ static int snd_pcm_oss_set_subdivide(str
if (substream == NULL)
continue;
runtime = substream->runtime;
+ if (atomic_read(&runtime->oss.rw_ref))
+ return -EBUSY;
if (mutex_lock_interruptible(&runtime->oss.params_lock))
return -ERESTARTSYS;
err = snd_pcm_oss_set_subdivide1(substream, subdivide);
@@ -1990,6 +2005,8 @@ static int snd_pcm_oss_set_fragment(stru
if (substream == NULL)
continue;
runtime = substream->runtime;
+ if (atomic_read(&runtime->oss.rw_ref))
+ return -EBUSY;
if (mutex_lock_interruptible(&runtime->oss.params_lock))
return -ERESTARTSYS;
err = snd_pcm_oss_set_fragment1(substream, val);
@@ -2384,6 +2401,7 @@ static void snd_pcm_oss_init_substream(s
runtime->oss.maxfrags = 0;
runtime->oss.subdivision = 0;
substream->pcm_release = snd_pcm_oss_release_substream;
+ atomic_set(&runtime->oss.rw_ref, 0);
}

static int snd_pcm_oss_release_file(struct snd_pcm_oss_file *pcm_oss_file)