ASoC: dpcm: prevent snd_soc_dpcm use after free

The dpcm get from fe_clients/be_clients
may be free before use

Add a spin lock at snd_soc_card level,
to protect the dpcm instance.
The lock may be used in atomic context, so use spin lock.

Use irq spin lock version,
since the lock may be used in interrupts.

possible race condition between
void dpcm_be_disconnect(
	...
	list_del(&dpcm->list_be);
	list_del(&dpcm->list_fe);
	kfree(dpcm);
	...

and
	for_each_dpcm_fe()
	for_each_dpcm_be*()

race condition example
Thread 1:
    snd_soc_dapm_mixer_update_power()
        -> soc_dpcm_runtime_update()
            -> dpcm_be_disconnect()
                -> kfree(dpcm);
Thread 2:
    dpcm_fe_dai_trigger()
        -> dpcm_be_dai_trigger()
            -> snd_soc_dpcm_can_be_free_stop()
                -> if (dpcm->fe == fe)

Excpetion Scenario:
	two FE link to same BE
	FE1 -> BE
	FE2 ->

	Thread 1: switch of mixer between FE2 -> BE
	Thread 2: pcm_stop FE1

Exception:

Unable to handle kernel paging request at virtual address dead0000000000e0

pc=<> [<ffffff8960e2cd10>] dpcm_be_dai_trigger+0x29c/0x47c
	sound/soc/soc-pcm.c:3226
		if (dpcm->fe == fe)
lr=<> [<ffffff8960e2f694>] dpcm_fe_dai_do_trigger+0x94/0x26c

Backtrace:
[<ffffff89602dba80>] notify_die+0x68/0xb8
[<ffffff896028c7dc>] die+0x118/0x2a8
[<ffffff89602a2f84>] __do_kernel_fault+0x13c/0x14c
[<ffffff89602a27f4>] do_translation_fault+0x64/0xa0
[<ffffff8960280cf8>] do_mem_abort+0x4c/0xd0
[<ffffff8960282ad0>] el1_da+0x24/0x40
[<ffffff8960e2cd10>] dpcm_be_dai_trigger+0x29c/0x47c
[<ffffff8960e2f694>] dpcm_fe_dai_do_trigger+0x94/0x26c
[<ffffff8960e2edec>] dpcm_fe_dai_trigger+0x3c/0x44
[<ffffff8960de5588>] snd_pcm_do_stop+0x50/0x5c
[<ffffff8960dded24>] snd_pcm_action+0xb4/0x13c
[<ffffff8960ddfdb4>] snd_pcm_drop+0xa0/0x128
[<ffffff8960de69bc>] snd_pcm_common_ioctl+0x9d8/0x30f0
[<ffffff8960de1cac>] snd_pcm_ioctl_compat+0x29c/0x2f14
[<ffffff89604c9d60>] compat_SyS_ioctl+0x128/0x244
[<ffffff8960283740>] el0_svc_naked+0x34/0x38
[<ffffffffffffffff>] 0xffffffffffffffff

Signed-off-by: KaiChieh Chuang <kaichieh.chuang@mediatek.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

2 files changed, 34 insertions, 7 deletions

diff --git a/sound/soc/soc-core.c b/sound/soc/soc-core.c
index 5a5764dba147..d88757659729 100644
--- a/sound/soc/soc-core.c
+++ b/sound/soc/soc-core.c
@@ -2820,6 +2820,7 @@ int snd_soc_register_card(struct snd_soc_card *card)
 	card->instantiated = 0;
 	mutex_init(&card->mutex);
 	mutex_init(&card->dapm_mutex);
+	spin_lock_init(&card->dpcm_lock);
 
 	return snd_soc_bind_card(card);
 }
diff --git a/sound/soc/soc-pcm.c b/sound/soc/soc-pcm.c
index e70555a4ea06..90504c149931 100644
--- a/sound/soc/soc-pcm.c
+++ b/sound/soc/soc-pcm.c
@@ -1216,6 +1216,7 @@ static int dpcm_be_connect(struct snd_soc_pcm_runtime *fe,
 		struct snd_soc_pcm_runtime *be, int stream)
 {
 	struct snd_soc_dpcm *dpcm;
+	unsigned long flags;
 
 	/* only add new dpcms */
 	for_each_dpcm_be(fe, stream, dpcm) {
@@ -1231,8 +1232,10 @@ static int dpcm_be_connect(struct snd_soc_pcm_runtime *fe,
 	dpcm->fe = fe;
 	be->dpcm[stream].runtime = fe->dpcm[stream].runtime;
 	dpcm->state = SND_SOC_DPCM_LINK_STATE_NEW;
+	spin_lock_irqsave(&fe->card->dpcm_lock, flags);
 	list_add(&dpcm->list_be, &fe->dpcm[stream].be_clients);
 	list_add(&dpcm->list_fe, &be->dpcm[stream].fe_clients);
+	spin_unlock_irqrestore(&fe->card->dpcm_lock, flags);
 
 	dev_dbg(fe->dev, "connected new DPCM %s path %s %s %s\n",
 			stream ? "capture" : "playback",  fe->dai_link->name,
@@ -1278,6 +1281,7 @@ static void dpcm_be_reparent(struct snd_soc_pcm_runtime *fe,
 void dpcm_be_disconnect(struct snd_soc_pcm_runtime *fe, int stream)
 {
 	struct snd_soc_dpcm *dpcm, *d;
+	unsigned long flags;
 
 	for_each_dpcm_be_safe(fe, stream, dpcm, d) {
 		dev_dbg(fe->dev, "ASoC: BE %s disconnect check for %s\n",
@@ -1297,8 +1301,10 @@ void dpcm_be_disconnect(struct snd_soc_pcm_runtime *fe, int stream)
 #ifdef CONFIG_DEBUG_FS
 		debugfs_remove(dpcm->debugfs_state);
 #endif
+		spin_lock_irqsave(&fe->card->dpcm_lock, flags);
 		list_del(&dpcm->list_be);
 		list_del(&dpcm->list_fe);
+		spin_unlock_irqrestore(&fe->card->dpcm_lock, flags);
 		kfree(dpcm);
 	}
 }
@@ -1550,10 +1556,13 @@ int dpcm_process_paths(struct snd_soc_pcm_runtime *fe,
 void dpcm_clear_pending_state(struct snd_soc_pcm_runtime *fe, int stream)
 {
 	struct snd_soc_dpcm *dpcm;
+	unsigned long flags;
 
+	spin_lock_irqsave(&fe->card->dpcm_lock, flags);
 	for_each_dpcm_be(fe, stream, dpcm)
 		dpcm->be->dpcm[stream].runtime_update =
 						SND_SOC_DPCM_UPDATE_NO;
+	spin_unlock_irqrestore(&fe->card->dpcm_lock, flags);
 }
 
 static void dpcm_be_dai_startup_unwind(struct snd_soc_pcm_runtime *fe,
@@ -2574,6 +2583,7 @@ static int dpcm_run_update_startup(struct snd_soc_pcm_runtime *fe, int stream)
 	struct snd_soc_dpcm *dpcm;
 	enum snd_soc_dpcm_trigger trigger = fe->dai_link->trigger[stream];
 	int ret;
+	unsigned long flags;
 
 	dev_dbg(fe->dev, "ASoC: runtime %s open on FE %s\n",
 			stream ? "capture" : "playback", fe->dai_link->name);
@@ -2643,11 +2653,13 @@ close:
 	dpcm_be_dai_shutdown(fe, stream);
 disconnect:
 	/* disconnect any non started BEs */
+	spin_lock_irqsave(&fe->card->dpcm_lock, flags);
 	for_each_dpcm_be(fe, stream, dpcm) {
 		struct snd_soc_pcm_runtime *be = dpcm->be;
 		if (be->dpcm[stream].state != SND_SOC_DPCM_STATE_START)
 				dpcm->state = SND_SOC_DPCM_LINK_STATE_FREE;
 	}
+	spin_unlock_irqrestore(&fe->card->dpcm_lock, flags);
 
 	return ret;
 }
@@ -3223,7 +3235,10 @@ int snd_soc_dpcm_can_be_free_stop(struct snd_soc_pcm_runtime *fe,
 {
 	struct snd_soc_dpcm *dpcm;
 	int state;
+	int ret = 1;
+	unsigned long flags;
 
+	spin_lock_irqsave(&fe->card->dpcm_lock, flags);
 	for_each_dpcm_fe(be, stream, dpcm) {
 
 		if (dpcm->fe == fe)
@@ -3232,12 +3247,15 @@ int snd_soc_dpcm_can_be_free_stop(struct snd_soc_pcm_runtime *fe,
 		state = dpcm->fe->dpcm[stream].state;
 		if (state == SND_SOC_DPCM_STATE_START ||
 			state == SND_SOC_DPCM_STATE_PAUSED ||
-			state == SND_SOC_DPCM_STATE_SUSPEND)
-			return 0;
+			state == SND_SOC_DPCM_STATE_SUSPEND) {
+			ret = 0;
+			break;
+		}
 	}
+	spin_unlock_irqrestore(&fe->card->dpcm_lock, flags);
 
 	/* it's safe to free/stop this BE DAI */
-	return 1;
+	return ret;
 }
 EXPORT_SYMBOL_GPL(snd_soc_dpcm_can_be_free_stop);
 
@@ -3250,7 +3268,10 @@ int snd_soc_dpcm_can_be_params(struct snd_soc_pcm_runtime *fe,
 {
 	struct snd_soc_dpcm *dpcm;
 	int state;
+	int ret = 1;
+	unsigned long flags;
 
+	spin_lock_irqsave(&fe->card->dpcm_lock, flags);
 	for_each_dpcm_fe(be, stream, dpcm) {
 
 		if (dpcm->fe == fe)
@@ -3260,12 +3281,15 @@ int snd_soc_dpcm_can_be_params(struct snd_soc_pcm_runtime *fe,
 		if (state == SND_SOC_DPCM_STATE_START ||
 			state == SND_SOC_DPCM_STATE_PAUSED ||
 			state == SND_SOC_DPCM_STATE_SUSPEND ||
-			state == SND_SOC_DPCM_STATE_PREPARE)
-			return 0;
+			state == SND_SOC_DPCM_STATE_PREPARE) {
+			ret = 0;
+			break;
+		}
 	}
+	spin_unlock_irqrestore(&fe->card->dpcm_lock, flags);
 
 	/* it's safe to change hw_params */
-	return 1;
+	return ret;
 }
 EXPORT_SYMBOL_GPL(snd_soc_dpcm_can_be_params);
 
@@ -3304,6 +3328,7 @@ static ssize_t dpcm_show_state(struct snd_soc_pcm_runtime *fe,
 	struct snd_pcm_hw_params *params = &fe->dpcm[stream].hw_params;
 	struct snd_soc_dpcm *dpcm;
 	ssize_t offset = 0;
+	unsigned long flags;
 
 	/* FE state */
 	offset += snprintf(buf + offset, size - offset,
@@ -3331,6 +3356,7 @@ static ssize_t dpcm_show_state(struct snd_soc_pcm_runtime *fe,
 		goto out;
 	}
 
+	spin_lock_irqsave(&fe->card->dpcm_lock, flags);
 	for_each_dpcm_be(fe, stream, dpcm) {
 		struct snd_soc_pcm_runtime *be = dpcm->be;
 		params = &dpcm->hw_params;
@@ -3351,7 +3377,7 @@ static ssize_t dpcm_show_state(struct snd_soc_pcm_runtime *fe,
 				params_channels(params),
 				params_rate(params));
 	}
-
+	spin_unlock_irqrestore(&fe->card->dpcm_lock, flags);
 out:
 	return offset;
 }