Hi, there is a new null-ptr-deref Write bug in snd_pcm_format_set_slience in sound/core/pcm_misc.c in the latest upstream kernel and can reproduce it. We call SNDCTL_DSP_SYNC and SNDCTL_DSP_SPEED in multiple threads to trigger the vulnerability.

See the Call Trace: ================================================================== Call Trace: <TASK> __dump_stack lib/dump_stack.c:88 [inline] dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106 kasan_report+0xb1/0x1e0 mm/kasan/report.c:495 check_region_inline mm/kasan/generic.c:183 [inline] kasan_check_range+0x13d/0x180 mm/kasan/generic.c:189 memset+0x20/0x40 mm/kasan/shadow.c:44 snd_pcm_format_set_silence sound/core/pcm_misc.c:441 [inline] snd_pcm_format_set_silence+0x215/0x350 sound/core/pcm_misc.c:424 snd_pcm_oss_sync+0x60e/0x800 sound/core/oss/pcm_oss.c:1690 snd_pcm_oss_ioctl+0x2087/0x3420 sound/core/oss/pcm_oss.c:2634 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:870 [inline] __se_sys_ioctl fs/ioctl.c:856 [inline] __x64_sys_ioctl+0x193/0x200 fs/ioctl.c:856 do_syscall_x64 arch/x86/entry/common.c:50 [inline] do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x63/0xcd ================================================================== We can see the function snd_pcm_format_set_silence code below: ``` int snd_pcm_format_set_silence(snd_pcm_format_t format, void *data, unsigned int samples) { int width; unsigned char *dst; const unsigned char *pat;

if (!valid_format(format)) return -EINVAL; if (samples == 0) return 0; width = pcm_formats[(INT)format].phys; /* physical width */ pat = pcm_formats[(INT)format].silence; if (!width || !pat) return -EINVAL; /* signed or 1 byte data */ if (pcm_formats[(INT)format].signd == 1 || width <= 8) { unsigned int bytes = samples * width / 8; memset(data, *pat, bytes); ///// [1] ---------> data is NULL return 0; } ...... } ``` [1], the data pointer is NULL, we can know snd_pcm_format_set_silence called in line 1690 in sound/core/oss/pcm_oss.c from call stack trace. let we see code below: ``` static int snd_pcm_oss_sync(struct snd_pcm_oss_file *pcm_oss_file) { int err = 0; unsigned int saved_f_flags; struct snd_pcm_substream *substream; struct snd_pcm_runtime *runtime; snd_pcm_format_t format; unsigned long width; size_t size;

substream = pcm_oss_file->streams[SNDRV_PCM_STREAM_PLAYBACK]; if (substream != NULL) { runtime = substream->runtime; if (atomic_read(&substream->mmap_count)) goto __direct; err = snd_pcm_oss_make_ready(substream); if (err < 0) return err; atomic_inc(&runtime->oss.rw_ref); if (mutex_lock_interruptible(&runtime->oss.params_lock)) { atomic_dec(&runtime->oss.rw_ref); return -ERESTARTSYS; } format = snd_pcm_oss_format_from(runtime->oss.format); width = snd_pcm_format_physical_width(format); if (runtime->oss.buffer_used > 0) { #ifdef OSS_DEBUG pcm_dbg(substream->pcm, "sync: buffer_used\n"); #endif size = (8 * (runtime->oss.period_bytes - runtime->oss.buffer_used) + 7) / width; snd_pcm_format_set_silence(format, runtime->oss.buffer + runtime->oss.buffer_used, ///// [2] size); err = snd_pcm_oss_sync1(substream, runtime->oss.period_bytes); if (err < 0) goto unlock; } else if (runtime->oss.period_ptr > 0) {

``` [2] runtime->oss.buffer + runtime->oss.buffer_used is the data pointer, but runtime->oss.buffer is NULL here but it doesn't make sense. runtime->oss.buffter is allocated by kvzalloc, if runtime->oss_buffer is NULL, it would return an ENOMEM error. Maybe I think there is a race condition, the runtime->oss.buffer is freed and set to NULL but we can use runtime->oss.buffter via ioctl.

###reproduce it [ 167.258988][T25615] ================================================================== [ 167.265917][T25615] BUG: KASAN: null-ptr-deref in snd_pcm_format_set_silence+0x215/0x350 [ 167.266704][T25615] Write of size 16383 at addr 0000000000000001 by task snd_pcm_format_/25615 [ 167.267506][T25615] [ 167.267732][T25615] CPU: 0 PID: 25615 Comm: snd_pcm_format_ Not tainted 6.0.0-rc3-00299-gd895ec7938c4 #11 [ 167.268617][T25615] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-2 04/01/2014 [ 167.269410][T25615] Call Trace: [ 167.269697][T25615] <TASK> [ 167.269977][T25615] dump_stack_lvl+0xcd/0x134 [ 167.270428][T25615] ? snd_pcm_format_set_silence+0x215/0x350 [ 167.270985][T25615] kasan_report+0xb1/0x1e0 [ 167.271405][T25615] ? snd_pcm_format_set_silence+0x215/0x350 [ 167.271964][T25615] kasan_check_range+0x13d/0x180 [ 167.272440][T25615] memset+0x20/0x40 [ 167.272809][T25615] snd_pcm_format_set_silence+0x215/0x350 [ 167.273366][T25615] snd_pcm_oss_sync+0x60e/0x800 [ 167.273831][T25615] snd_pcm_oss_ioctl+0x2087/0x3420 [ 167.274320][T25615] ? snd_pcm_oss_release+0x300/0x300 [ 167.274817][T25615] ? __fget_files+0x26a/0x440 [ 167.275262][T25615] ? bpf_lsm_file_ioctl+0x5/0x10 [ 167.275731][T25615] ? snd_pcm_oss_release+0x300/0x300 [ 167.276222][T25615] __x64_sys_ioctl+0x193/0x200 [ 167.276677][T25615] do_syscall_64+0x35/0xb0 [ 167.277108][T25615] entry_SYSCALL_64_after_hwframe+0x63/0xcd [ 167.277679][T25615] RIP: 0033:0x44af9d [ 167.278058][T25615] Code: 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 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 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff 8 [ 167.279792][T25615] RSP: 002b:00007f0cb636a178 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 [ 167.280546][T25615] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 000000000044af9d [ 167.281285][T25615] RDX: 0000000000000000 RSI: 0000000000005001 RDI: 0000000000000003 [ 167.282001][T25615] RBP: 00007f0cb636a1a0 R08: 0000000000000000 R09: 0000000000000000 [ 167.282715][T25615] R10: 0000000000000000 R11: 0000000000000246 R12: 00007ffcfea8e08e [ 167.283432][T25615] R13: 00007ffcfea8e08f R14: 0000000000000000 R15: 00007f0cb636a640 [ 167.284164][T25615] </TASK> [ 167.284453][T25615] ==================================================================

If needed I would provide a reproduce.

Regards, butt3rflyh4ck.

-- Active Defense Lab of Venustech