Re: A divide error bug in snd_pcm_write

[Takashi Iwai <tiwai@suse.de>]

On Mon, 26 Sep 2022 11:26:17 +0200,
butt3rflyh4ck wrote:
> 
> Hi, there is a divide error bug in snd_pcm_write in
> sound/core/pcm_native.c in the latest kernel.
> 
> ##Root Cause
> When open the device of /dev/snd/pcmC#D#p, there would attach a
> runtime to pcm->substream via snd_pcm_open_substream. see the code
> below:
> ```
> int snd_pcm_attach_substream(struct snd_pcm *pcm, int stream,
>     struct file *file,
>     struct snd_pcm_substream **rsubstream)
> {
> ......
> 
>  runtime = kzalloc(sizeof(*runtime), GFP_KERNEL);
> if (runtime == NULL)
> return -ENOMEM;
> 
> size = PAGE_ALIGN(sizeof(struct snd_pcm_mmap_status));
> runtime->status = alloc_pages_exact(size, GFP_KERNEL);
> if (runtime->status == NULL) {
> kfree(runtime);
> return -ENOMEM;
> }
> memset(runtime->status, 0, size);
> 
> size = PAGE_ALIGN(sizeof(struct snd_pcm_mmap_control));
> runtime->control = alloc_pages_exact(size, GFP_KERNEL);
> if (runtime->control == NULL) {
> free_pages_exact(runtime->status,
>       PAGE_ALIGN(sizeof(struct snd_pcm_mmap_status)));
> kfree(runtime);
> return -ENOMEM;
> }
> memset(runtime->control, 0, size);
> 
> init_waitqueue_head(&runtime->sleep);
> init_waitqueue_head(&runtime->tsleep);
> 
> runtime->status->state = SNDRV_PCM_STATE_OPEN;
> mutex_init(&runtime->buffer_mutex);
> atomic_set(&runtime->buffer_accessing, 0);
> 
> substream->runtime = runtime;
> substream->private_data = pcm->private_data;
> substream->ref_count = 1;
> substream->f_flags = file->f_flags;
> substream->pid = get_pid(task_pid(current));
> pstr->substream_opened++;
> *rsubstream = substream;
> return 0;
> }
> ```
> It would kzmalloc a new runtime. And initialize runtime simply.
> If we write some data to the device. it would call snd_pcm_write or
> snd_pcm_writev. and read some date from the device, it would call
> snd_pcm_read or snd_pcm_readv.
> Anyway, the four function would use data of runtime, but some data of
> runtime is NULL not be initialized, see the code below:
> ```
> static ssize_t snd_pcm_write(struct file *file, const char __user *buf,
>     size_t count, loff_t * offset)
> {
> struct snd_pcm_file *pcm_file;
> struct snd_pcm_substream *substream;
> struct snd_pcm_runtime *runtime;
> snd_pcm_sframes_t result;
> 
> pcm_file = file->private_data;
> substream = pcm_file->substream;
> if (PCM_RUNTIME_CHECK(substream))
> return -ENXIO;
> runtime = substream->runtime;
> if (runtime->status->state == SNDRV_PCM_STATE_OPEN ||
>    runtime->status->state == SNDRV_PCM_STATE_DISCONNECTED)
> return -EBADFD;
> if (!frame_aligned(runtime, count))    ///////  [1]
> return -EINVAL;
> count = bytes_to_frames(runtime, count);    /////// [2]
> result = snd_pcm_lib_write(substream, buf, count);
> if (result > 0)
> result = frames_to_bytes(runtime, result);
> return result;
> }
> ```
> [1] call frame_aligned to aligned.
> ```
> static inline int frame_aligned(struct snd_pcm_runtime *runtime, ssize_t bytes)
> {
> return bytes % runtime->byte_align == 0;
> }
> ```
> but runtime->byte_align is NULL.
> 
> [2] call bytes_to_frames.
> ```
> static inline ssize_t frames_to_bytes(struct snd_pcm_runtime *runtime,
> snd_pcm_sframes_t size)
> {
> return size * runtime->frame_bits / 8;
> }
> ```
> but runtime->frame_bits is NULL.
> 
> ##reproduce it
> [ 1189.305083][ T4656] divide error: 0000 [#1] PREEMPT SMP
> [ 1189.305600][ T4656] CPU: 1 PID: 4656 Comm: snd_pcm_write Not
> tainted 6.0.0-rc7 #16
> [ 1189.306157][ T4656] Hardware name: QEMU Standard PC (i440FX + PIIX,
> 1996), BIOS 1.13.0-1ubuntu1 04/01/2014
> [ 1189.306760][ T4656] RIP: 0010:snd_pcm_write+0x33/0xa0
> [ 1189.307155][ T4656] Code: 8b 38 48 85 ff 74 72 48 8b 9f c0 00 00 00
> 48 85 db 74 66 48 8b 83 00 01 00 00 f7 00 f7 ff ff ff 74 6b 48 89 d0
> 48 89 d1 31 d2 <48> f7 b3 91
> [ 1189.308553][ T4656] RSP: 0018:ffffc9000adc7e68 EFLAGS: 00010246
> [ 1189.309034][ T4656] RAX: 0000000000000000 RBX: ffff888048ec2000
> RCX: 0000000000000000
> [ 1189.309583][ T4656] RDX: 0000000000000000 RSI: 0000000000000000
> RDI: ffff888046fc9c00
> [ 1189.310163][ T4656] RBP: 0000000000000000 R08: 0000000000000000
> R09: 0000000000020026
> [ 1189.310679][ T4656] R10: 0000000000000001 R11: 0000000000000000
> R12: 0000000000000000
> [ 1189.311226][ T4656] R13: ffffc9000adc7f08 R14: 0000000000000000
> R15: 0000000000000000
> [ 1189.311754][ T4656] FS:  00000000012d8880(0000)
> GS:ffff88807ec00000(0000) knlGS:0000000000000000
> [ 1189.312350][ T4656] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [ 1189.312780][ T4656] CR2: 0000000020000000 CR3: 000000004b496000
> CR4: 00000000000006e0
> [ 1189.313234][ T4656] Call Trace:
> [ 1189.313424][ T4656]  <TASK>
> [ 1189.313597][ T4656]  vfs_write+0xe6/0x4d0
> [ 1189.313836][ T4656]  ksys_write+0x60/0xe0
> [ 1189.314071][ T4656]  do_syscall_64+0x35/0xb0
> [ 1189.314324][ T4656]  entry_SYSCALL_64_after_hwframe+0x63/0xcd
> [ 1189.314734][ T4656] RIP: 0033:0x44dc3d
> [ 1189.315007][ T4656] Code: 28 c3 e8 36 29 00 00 66 0f 1f 44 00 00 f3
> 0f 1e fa 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b
> 4c 24 08 0f 05 <48> 3d 01 f8
> [ 1189.316338][ T4656] RSP: 002b:00007ffcbdf5ef38 EFLAGS: 00000246
> ORIG_RAX: 0000000000000001
> [ 1189.317012][ T4656] RAX: ffffffffffffffda RBX: 0000000000400530
> RCX: 000000000044dc3d
> [ 1189.317693][ T4656] RDX: 0000000000000000 RSI: 0000000000000000
> RDI: 0000000000000003
> [ 1189.318172][ T4656] RBP: 00007ffcbdf5ef50 R08: 0000000082000000
> R09: 0000000000000000
> [ 1189.318648][ T4656] R10: 000000000000ffff R11: 0000000000000246
> R12: 00000000004030a0
> [ 1189.319182][ T4656] R13: 0000000000000000 R14: 00000000004c5018
> R15: 0000000000000000

The question is how the code passes the check before [1]:

 if (runtime->status->state == SNDRV_PCM_STATE_OPEN ||
     runtime->status->state == SNDRV_PCM_STATE_DISCONNECTED)
	return -EBADFD;

The uninitialized state should have been with SNDRV_PCM_STATE_OPEN,
and runtime->byte_align is set up at snd_pcm_hw_params() followed by
snd_pcm-set_state() to chage the state to SNDRV_PCM_STATE_SETUP.

Which kernel version are you testing?


Takashi