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