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Wed, 14 Oct 2026 12:54:50 +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 r7zvOZl7z2r9FgAAD6G6ig (envelope-from ); Wed, 14 Oct 2026 12:54:50 +0000 Date: Wed, 14 Oct 2026 14:54:49 +0200 Message-ID: <87zewgcuhy.wl-tiwai@suse.de> From: Takashi Iwai To: Cen Zhang Cc: perex@perex.cz, tiwai@suse.com, phucduc.bui@gmail.com, cezary.rojewski@intel.com, cassiogabrielcontato@gmail.com, kees+treewide@kernel.org, yilinzhang@moonshot.ai, sammiee5311@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, tiwai@suse.de Subject: Re: [PATCH v2] ALSA: pcm: Unlink substreams before releasing them In-Reply-To: References: User-Agent: Wanderlust/2.15.9 (Almost Unreal) Emacs/30.2 Mule/6.0 Precedence: bulk X-Mailing-List: linux-kernel@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_VIA_SMTP_AUTH(0.00)[]; RCPT_COUNT_TWELVE(0.00)[17]; FREEMAIL_TO(0.00)[gmail.com]; MIME_TRACE(0.00)[0:+]; TAGGED_RCPT(0.00)[treewide]; ARC_NA(0.00)[]; FREEMAIL_ENVRCPT(0.00)[gmail.com]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FROM_HAS_DN(0.00)[]; FREEMAIL_CC(0.00)[perex.cz,suse.com,gmail.com,intel.com,kernel.org,moonshot.ai,linutronix.de,vger.kernel.org,suse.de]; TO_DN_SOME(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; RCVD_TLS_ALL(0.00)[]; TO_MATCH_ENVRCPT_SOME(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.de:email,imap1.dmz-prg2.suse.org:helo] X-Spam-Score: -1.80 X-Spam-Level: X-Spam-Flag: NO On Wed, 14 Oct 2026 12:52:15 +0200, Cen Zhang wrote: > > A closing PCM substream can remain in its linked group after the > driver close callback has freed its private data. With two configured > dummy capture substreams on the same PCM device, linked with LINK, > PREPARE on the surviving substream can still visit the closing member: > > Final close of A PREPARE on linked B > ---------------- ------------------- > snd_pcm_drop(): group -> SETUP > do_hw_free(A) > dummy_pcm_close(A): free dpcm > Take snd_pcm_link_rwsem for reading > Walk the group, including A > dummy_pcm_prepare(A) > Read freed timer_ops > pcm_release_private(A) > snd_pcm_unlink(A) > > Unlink at the start of final substream release, before dropping the > stream or releasing driver resources. The link write lock waits for > an existing group PREPARE, and unlink removes the closing member from > later group actions. Keep the existing stop synchronization in > do_hw_free() before the driver resources are freed. > > Make unlink independent of the pcm_release callback so OSS substreams > are covered too. Remove the native-only unlink callback and its > registration, while retaining the callback hook for OSS cleanup. > > The existing KASAN report below records the freed timer_ops read in > dummy_pcm_prepare(). > > 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: 1576274d3028 ("[ALSA] Fix Oops of PCM OSS emulation") > Suggested-by: Takashi Iwai > Signed-off-by: Cen Zhang Applied to for-next branch now. A problem with racy link removal Sashiko suggested is an interesting case to be revisited, but it's no regression and can be triggered independently from this change. Takashi