[PATCH v2] ASoC: dpcm: prevent snd_soc_dpcm use after free

[KaiChieh Chuang <kaichieh.chuang-NuS5LvNUpcJWk0Htik3J/w@public.gmane.org>]

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.

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-NuS5LvNUpcJWk0Htik3J/w@public.gmane.org>
---
 include/sound/soc.h  |  2 ++
 sound/soc/soc-core.c |  1 +
 sound/soc/soc-pcm.c  | 33 ++++++++++++++++++++++++++-------
 3 files changed, 29 insertions(+), 7 deletions(-)

diff --git a/include/sound/soc.h b/include/sound/soc.h
index eb7db60..1e2be35 100644
--- a/include/sound/soc.h
+++ b/include/sound/soc.h
@@ -1083,6 +1083,8 @@ struct snd_soc_card {
 	struct mutex mutex;
 	struct mutex dapm_mutex;
 
+	spinlock_t dpcm_lock;
+
 	bool instantiated;
 	bool topology_shortname_created;
 
diff --git a/sound/soc/soc-core.c b/sound/soc/soc-core.c
index 5a5764d..d887576 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 a5b40e8..9020a06 100644
--- a/sound/soc/soc-pcm.c
+++ b/sound/soc/soc-pcm.c
@@ -1228,8 +1228,10 @@ 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(&fe->card->dpcm_lock);
 	list_add(&dpcm->list_be, &fe->dpcm[stream].be_clients);
 	list_add(&dpcm->list_fe, &be->dpcm[stream].fe_clients);
+	spin_unlock(&fe->card->dpcm_lock);
 
 	dev_dbg(fe->dev, "connected new DPCM %s path %s %s %s\n",
 			stream ? "capture" : "playback",  fe->dai_link->name,
@@ -1294,8 +1296,10 @@ void dpcm_be_disconnect(struct snd_soc_pcm_runtime *fe, int stream)
 #ifdef CONFIG_DEBUG_FS
 		debugfs_remove(dpcm->debugfs_state);
 #endif
+		spin_lock(&fe->card->dpcm_lock);
 		list_del(&dpcm->list_be);
 		list_del(&dpcm->list_fe);
+		spin_unlock(&fe->card->dpcm_lock);
 		kfree(dpcm);
 	}
 }
@@ -1548,9 +1552,11 @@ void dpcm_clear_pending_state(struct snd_soc_pcm_runtime *fe, int stream)
 {
 	struct snd_soc_dpcm *dpcm;
 
+	spin_lock(&fe->card->dpcm_lock);
 	for_each_dpcm_be(fe, stream, dpcm)
 		dpcm->be->dpcm[stream].runtime_update =
 						SND_SOC_DPCM_UPDATE_NO;
+	spin_unlock(&fe->card->dpcm_lock);
 }
 
 static void dpcm_be_dai_startup_unwind(struct snd_soc_pcm_runtime *fe,
@@ -2640,11 +2646,13 @@ static int dpcm_run_update_startup(struct snd_soc_pcm_runtime *fe, int stream)
 	dpcm_be_dai_shutdown(fe, stream);
 disconnect:
 	/* disconnect any non started BEs */
+	spin_lock(&fe->card->dpcm_lock);
 	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(&fe->card->dpcm_lock);
 
 	return ret;
 }
@@ -3220,7 +3228,9 @@ int snd_soc_dpcm_can_be_free_stop(struct snd_soc_pcm_runtime *fe,
 {
 	struct snd_soc_dpcm *dpcm;
 	int state;
+	int ret = 1;
 
+	spin_lock(&fe->card->dpcm_lock);
 	for_each_dpcm_fe(be, stream, dpcm) {
 
 		if (dpcm->fe == fe)
@@ -3229,12 +3239,15 @@ 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(&fe->card->dpcm_lock);
 
 	/* it's safe to free/stop this BE DAI */
-	return 1;
+	return ret;
 }
 EXPORT_SYMBOL_GPL(snd_soc_dpcm_can_be_free_stop);
 
@@ -3247,7 +3260,9 @@ int snd_soc_dpcm_can_be_params(struct snd_soc_pcm_runtime *fe,
 {
 	struct snd_soc_dpcm *dpcm;
 	int state;
+	int ret = 1;
 
+	spin_lock(&fe->card->dpcm_lock);
 	for_each_dpcm_fe(be, stream, dpcm) {
 
 		if (dpcm->fe == fe)
@@ -3257,12 +3272,15 @@ 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(&fe->card->dpcm_lock);
 
 	/* it's safe to change hw_params */
-	return 1;
+	return ret;
 }
 EXPORT_SYMBOL_GPL(snd_soc_dpcm_can_be_params);
 
@@ -3328,6 +3346,7 @@ static ssize_t dpcm_show_state(struct snd_soc_pcm_runtime *fe,
 		goto out;
 	}
 
+	spin_lock(&fe->card->dpcm_lock);
 	for_each_dpcm_be(fe, stream, dpcm) {
 		struct snd_soc_pcm_runtime *be = dpcm->be;
 		params = &dpcm->hw_params;
@@ -3348,7 +3367,7 @@ static ssize_t dpcm_show_state(struct snd_soc_pcm_runtime *fe,
 				params_channels(params),
 				params_rate(params));
 	}
-
+	spin_unlock(&fe->card->dpcm_lock);
 out:
 	return offset;
 }
-- 
1.9.1