The latest kernel upstream. Yes, but using mmap, you can map the runtime->status page, and then copy the data through memcpy to overwrite the status->state data, or even more, which is incredible. this is debug log: ```` gef➤ c Continuing. Cannot remove breakpoints because program is no longer writable. Further execution is probably impossible.
Thread 2 hit Hardware access (read/write) watchpoint 7: *0xffff88804c5cb000
Old value = 0x0 New value = 0x7665642f 0xffffffff828501a9 in snd_pcm_write (file=<optimized out>, buf=0x20000000 "/dev/snd/pcmC#D#p", count=0x18, offset=0xffffc9000a81bf08) at sound/core/pcm_native.c:3494 3494 if (runtime->status->state == SNDRV_PCM_STATE_OPEN ||
0xffffffff82850199 <snd_pcm_write+25> (bad) [rsi+riz*2+0x48] 0xffffffff8285019d <snd_pcm_write+29> mov eax, DWORD PTR [rbx+0x100] 0xffffffff828501a3 <snd_pcm_write+35> test DWORD PTR [rax], 0xfffffff7 → 0xffffffff828501a9 <snd_pcm_write+41> je 0xffffffff82850216 <snd_pcm_write+150> NOT taken [Reason: !(Z)] 0xffffffff828501ab <snd_pcm_write+43> mov rax, rdx 0xffffffff828501ae <snd_pcm_write+46> mov rcx, rdx 0xffffffff828501b1 <snd_pcm_write+49> xor edx, edx 0xffffffff828501b3 <snd_pcm_write+51> div QWORD PTR [rbx+0x90] 0xffffffff828501ba <snd_pcm_write+58> test rdx, rdx [!] Command 'context' failed to execute properly, reason: argument of type 'NoneType' is not iterable gef➤ p/x 0xffff88804c5cb000 $14 = 0xffff88804c5cb000 gef➤ x/10gx 0xffff88804c5cb000 0xffff88804c5cb000: 0x646e732f7665642f 0x234423436d63702f 0xffff88804c5cb010: 0x0000000000000070 0x0000000000000000 0xffff88804c5cb020: 0x0000000000000000 0x0000000000000000 0xffff88804c5cb030: 0x0000000000000000 0x0000000000000000 0xffff88804c5cb040: 0x0000000000000000 0x0000000000000000 gef➤ x/s 0xffff88804c5cb000 0xffff88804c5cb000: "/dev/snd/pcmC#D#p" gef➤ p/x *(struct snd_pcm_mmap_status *)0xffff88804c5cb000 $15 = { state = 0x7665642f, pad1 = 0x646e732f, __pad1 = 0xffff88804c5cb008, hw_ptr = 0x234423436d63702f, __pad2 = 0xffff88804c5cb010, tstamp = { tv_sec = 0x70, tv_nsec = 0x0 }, suspended_state = 0x0, pad3 = 0x0, audio_tstamp = { tv_sec = 0x0, tv_nsec = 0x0 } } gef➤ ````
Regards, butt3rflyh4ck.
On Mon, Sep 26, 2022 at 6:21 PM Takashi Iwai tiwai@suse.de wrote:
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
-- Active Defense Lab of Venustech