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Wed, 14 Oct 2026 07:19:41 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id IlQvAw0tz2oRcAAAD6G6ig (envelope-from ); Wed, 14 Oct 2026 07:19:41 +0000 Date: Wed, 14 Oct 2026 09:19:40 +0200 Message-ID: <877bjkg35f.wl-tiwai@suse.de> From: Takashi Iwai To: Cen Zhang Cc: perex@perex.cz, tiwai@suse.com, sammiee5311@gmail.com, phucduc.bui@gmail.com, kees@kernel.org, thomas.weissschuh@linutronix.de, tglx@kernel.org, linux-sound@vger.kernel.org, linux-kernel@vger.kernel.org, baijiaju1990@gmail.com, jjzuming@gmail.com Subject: Re: [PATCH] ALSA: dummy: Defer hrtimer data freeing until runtime detach In-Reply-To: References: User-Agent: Wanderlust/2.15.9 (Almost Unreal) Emacs/30.2 Mule/6.0 Precedence: bulk X-Mailing-List: linux-sound@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII X-Spamd-Result: default: False [-1.80 / 50.00]; BAYES_HAM(-3.00)[100.00%]; SUSPICIOUS_RECIPS(1.50)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; MID_CONTAINS_FROM(1.00)[]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; RCVD_TLS_ALL(0.00)[]; MIME_TRACE(0.00)[0:+]; ARC_NA(0.00)[]; TAGGED_RCPT(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; RCPT_COUNT_TWELVE(0.00)[12]; FREEMAIL_ENVRCPT(0.00)[gmail.com]; TO_DN_SOME(0.00)[]; FROM_HAS_DN(0.00)[]; FREEMAIL_CC(0.00)[perex.cz,suse.com,gmail.com,kernel.org,linutronix.de,vger.kernel.org]; FREEMAIL_TO(0.00)[gmail.com]; FROM_EQ_ENVFROM(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; TO_MATCH_ENVRCPT_ALL(0.00)[]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:helo] X-Spam-Score: -1.80 X-Spam-Level: X-Spam-Flag: NO On Wed, 14 Oct 2026 07:25:31 +0200, Cen Zhang wrote: > > The hrtimer record must remain alive while a linked PCM action can > visit its substream. dummy_pcm_close() frees that record before > pcm_release_private() unlinks the substream. runtime->private_data still > points to the freed allocation. > > With two configured dummy capture substreams linked and the hrtimer > backend selected, final close drops the group to SETUP. A surviving > peer can then issue PREPARE before the closing substream is unlinked: > > Target close Peer PREPARE > snd_pcm_drop(): group -> SETUP > do_hw_free() > dummy_pcm_close(): kfree(dpcm) > snd_pcm_action_nonatomic() > read-lock snd_pcm_link_rwsem > dummy_pcm_prepare() > read dpcm->timer_ops > pcm_release_private() > snd_pcm_unlink(): write-lock > > PREPARE holds the link read semaphore and the members' buffer mutexes, > but driver close holds neither across the free. Unlink's write lock > comes too late to protect the record. The ops-pointer read can use freed > memory and dispatch through an invalid function pointer. If PREPARE > already obtained the record before close, dummy_hrtimer_prepare() can > instead write period_time after it has been freed. The report below > shows the dispatch-time read and the ensuing fault; it does not show > the later write. > > Defer freeing the hrtimer record to runtime->private_free. Runtime > detach follows unlink, which waits for existing linked PREPARE actions > and prevents new ones from visiting the target. Cancel the embedded > timer in the destructor before releasing its storage. Register the > destructor from the backend free callback so the open error path also > releases the record through runtime detach. > > KASAN report as below: > > BUG: KASAN: slab-use-after-free in dummy_pcm_prepare+0xb7/0xc0 > Read of size 8 at addr ffff888106b35f00 by task alsa_pcm_fixtur/491 > > Call Trace: > > dump_stack_lvl+0x93/0xd0 > print_report+0xce/0x630 > ? dummy_pcm_prepare+0xb7/0xc0 > ? srso_alias_return_thunk+0x5/0xfbef5 > ? __virt_addr_valid+0x20d/0x410 > ? dummy_pcm_prepare+0xb7/0xc0 > kasan_report+0xe0/0x110 > ? dummy_pcm_prepare+0xb7/0xc0 > dummy_pcm_prepare+0xb7/0xc0 > snd_pcm_do_prepare+0x71/0xb0 > snd_pcm_action_group+0x505/0xb30 > snd_pcm_action_nonatomic+0xab/0x150 > snd_pcm_common_ioctl+0x1bf5/0x3a50 > ? srso_alias_return_thunk+0x5/0xfbef5 > ? do_vfs_ioctl+0x1f5/0x1280 > ? __pfx_do_vfs_ioctl+0x10/0x10 > ? ioctl_has_perm.constprop.0.isra.0+0x34f/0x500 > ? __pfx_snd_pcm_common_ioctl+0x10/0x10 > ? __fput+0x5ba/0xa60 > ? srso_alias_return_thunk+0x5/0xfbef5 > snd_pcm_ioctl+0x76/0xb0 > ? __pfx_snd_pcm_ioctl+0x10/0x10 > __x64_sys_ioctl+0x163/0x1d0 > do_syscall_64+0x115/0x6a0 > entry_SYSCALL_64_after_hwframe+0x77/0x7f > RIP: 0033:0x41ee8d > Code: 04 25 28 00 00 00 48 89 45 c8 31 c0 48 8d 45 10 c7 45 b0 10 00 00 00 48 89 45 b8 48 8d 45 d0 48 89 45 c0 b8 10 00 00 00 0f 05 <89> c2 3d 00 f0 ff ff 77 1a 48 8b 45 c8 64 48 2b 04 25 28 00 00 00 > RSP: 002b:00007ffcfa72fb60 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 > RAX: ffffffffffffffda RBX: 0000000000000004 RCX: 000000000041ee8d > RDX: 0000000000000000 RSI: 0000000000004140 RDI: 0000000000000004 > RBP: 00007ffcfa72fbb0 R08: 00007ffcfa72fb98 R09: 0000000000000110 > R10: 0000000000000001 R11: 0000000000000246 R12: 00007ffcfa72fcd8 > R13: 00007ffcfa72fcf0 R14: 00000000004a8f28 R15: 0000000000000001 > > > Allocated by task 488: > kasan_save_stack+0x33/0x60 > kasan_save_track+0x14/0x30 > __kasan_kmalloc+0xaa/0xb0 > __kmalloc_cache_noprof+0x251/0x610 > dummy_hrtimer_create+0x4a/0x170 > dummy_pcm_open+0xe7/0x730 > snd_pcm_open_substream+0x926/0x1580 > snd_pcm_open+0x28d/0x6d0 > snd_pcm_capture_open+0x82/0xe0 > snd_open+0x1ec/0x3e0 > chrdev_open+0x21f/0x660 > do_dentry_open+0x5c8/0x1300 > vfs_open+0x87/0x390 > path_openat+0x2460/0x3cd0 > do_file_open+0x21e/0x470 > do_sys_openat2+0xf4/0x1b0 > __x64_sys_openat+0x136/0x1e0 > do_syscall_64+0x115/0x6a0 > entry_SYSCALL_64_after_hwframe+0x77/0x7f > > Freed by task 490: > kasan_save_stack+0x33/0x60 > kasan_save_track+0x14/0x30 > kasan_save_free_info+0x3b/0x60 > __kasan_slab_free+0x5f/0x80 > kfree+0x307/0x580 > dummy_hrtimer_free+0x72/0xe0 > dummy_pcm_close+0x9f/0xd0 > snd_pcm_release_substream.part.0+0x104/0x310 > snd_pcm_release+0x106/0x240 > __fput+0x39f/0xa60 > fput_close_sync+0xff/0x200 > __x64_sys_close+0x8c/0xf0 > do_syscall_64+0x115/0x6a0 > entry_SYSCALL_64_after_hwframe+0x77/0x7f > ================================================================== > > Fixes: c631d03c6873 ("ALSA: dummy - Support high-res timer mode") > Signed-off-by: Cen Zhang > > --- > > diff --git a/sound/drivers/dummy.c b/sound/drivers/dummy.c > index 6b0a06e5c87638264e5d22deda1fe4bc028febe7..ae7cef9d74819a68dcf951a21768dccf38c7c4ad 100644 > --- a/sound/drivers/dummy.c > +++ b/sound/drivers/dummy.c > @@ -476,13 +476,20 @@ static int dummy_hrtimer_create(struct snd_pcm_substream *substream) > return 0; > } > > -static void dummy_hrtimer_free(struct snd_pcm_substream *substream) > +static void dummy_hrtimer_runtime_free(struct snd_pcm_runtime *runtime) > { > - struct dummy_hrtimer_pcm *dpcm = substream->runtime->private_data; > + struct dummy_hrtimer_pcm *dpcm = runtime->private_data; > > + hrtimer_cancel(&dpcm->timer); > kfree(dpcm); > } > > +static void dummy_hrtimer_free(struct snd_pcm_substream *substream) > +{ > + /* Linked PREPARE can still use the data until unlink. */ > + substream->runtime->private_free = dummy_hrtimer_runtime_free; > +} > + > static const struct dummy_timer_ops dummy_hrtimer_ops = { > .create = dummy_hrtimer_create, > .free = dummy_hrtimer_free, Hmm, it's not clear how this happens. It looks like a typical obscuration by AI reports... Basically dummy_hrtimer_sync_stop should handled the hrtimer cancel, but maybe the problem is rather its lack at releasing? If so, the patch below should cover instead. thanks, Takashi -- 8< -- --- a/sound/core/pcm_native.c +++ b/sound/core/pcm_native.c @@ -2301,6 +2301,8 @@ static int snd_pcm_drop(struct snd_pcm_substream *substream) result = snd_pcm_stop(substream, SNDRV_PCM_STATE_SETUP); /* runtime->control->appl_ptr = runtime->status->hw_ptr; */ + snd_pcm_sync_stop(substream, true); + return result; }