ASoC: dpcm: prevent snd_soc_dpcm use after free

ASoC: dpcm: prevent snd_soc_dpcm use after free

commit a9764869779081e8bf24da07ac040e8f3efcf13a upstream.

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>
[willmcvicker: move spinlock to bottom of struct snd_soc_card]
Signed-off-by: Will McVicker <willmcvicker@google.com>
Cc: stable@vger.kernel.org # 4.19+
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>