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Thu, 12 Nov 2026 12:36:38 +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 GHiUBtay9Wr4SwAAD6G6ig (envelope-from ); Thu, 12 Nov 2026 12:36:38 +0000 Date: Thu, 12 Nov 2026 13:36:37 +0100 Message-ID: <87mrrerzu2.wl-tiwai@suse.de> From: Takashi Iwai To: Sergei Nizovtsev Cc: Takashi Iwai , Jaroslav Kysela , Daniel Mack , linux-sound@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH] ALSA: caiaq: Kill EP1 URB before unregistering the input device In-Reply-To: <20261112094904.2430318-1-snizovtsev@cloudlinux.com> References: <20261112094904.2430318-1-snizovtsev@cloudlinux.com> User-Agent: Wanderlust/2.15.9 (Almost Unreal) Emacs/30.2 Mule/6.0 X-Mailing-List: stable@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII X-Spamd-Result: default: False [-12.51 / 50.00]; SUSE_INTERNAL_BYPASS(-9.00)[]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; MID_CONTAINS_FROM(1.00)[]; R_DKIM_ALLOW(-0.20)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; MX_GOOD(-0.01)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; ARC_NA(0.00)[]; RBL_SPAMHAUS_BLOCKED_OPENRESOLVER(0.00)[2a07:de40:b281:104:10:150:64:97:from]; MIME_TRACE(0.00)[0:+]; FREEMAIL_ENVRCPT(0.00)[gmail.com]; RCVD_TLS_ALL(0.00)[]; TO_DN_SOME(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; FREEMAIL_CC(0.00)[suse.com,perex.cz,gmail.com,vger.kernel.org]; RCPT_COUNT_SEVEN(0.00)[7]; RCVD_VIA_SMTP_AUTH(0.00)[]; RECEIVED_SPAMHAUS_BLOCKED_OPENRESOLVER(0.00)[2a07:de40:b281:106:10:150:64:167:received]; DKIM_TRACE(0.00)[suse.de:+]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:rdns,imap1.dmz-prg2.suse.org:helo,suse.de:dkim] X-Rspamd-Server: rspamd1.dmz-prg2.suse.org X-Rspamd-Action: no action X-Spam-Flag: NO X-Spam-Score: -12.51 X-Spam-Level: X-Rspamd-Queue-Id: 9C94821E08 On Thu, 12 Nov 2026 10:48:54 +0100, Sergei Nizovtsev wrote: > > snd_disconnect() unregisters the input device via > snd_usb_caiaq_input_disconnect() and only afterwards kills the EP1 > command URB (cdev->ep1_in_urb). The EP1 completion handler > usb_ep1_command_reply_dispatch() feeds snd_usb_caiaq_input_dispatch() > for EP1_CMD_READ_{ERP,ANALOG,IO} replies, which report into > cdev->input_dev. Since commit b04dcbb7f7b1 ("ALSA: caiaq: Use > snd_card_free_when_closed() at disconnection") the input device is > unregistered from snd_usb_caiaq_input_disconnect() but cdev->input_dev > is cleared only later, in snd_usb_caiaq_input_free() from the card > destructor. As the dispatch guard only tests cdev->input_dev for NULL, > an EP1 reply that completes after input_unregister_device() but before > cdev->ep1_in_urb is killed reports into an input device that has > already been unregistered and, with no evdev client holding it open, > freed. > > Normally the window is closed by the USB core: usb_unbind_interface() > calls usb_disable_interface() before ->disconnect(), which flushes the > EP1 URB as long as endpoint 0x81 belongs to the interface being > unbound. But caiaq addresses EP1 through the device-wide pipe > usb_rcvbulkpipe(usb_dev, 0x1) without checking which interface owns > the endpoint. If a device declares it in another interface, the URB > stays live across snd_disconnect() of the interface that owns the card. > > This needs a crafted device descriptor; a device that has EP1 in the > interface caiaq is bound to is not affected. > > Kill cdev->ep1_in_urb (and the paired midi_out_urb) before the input > and audio disconnect helpers, so no EP1 completion can run once the > input device has been unregistered. > > Reproduced under KASAN with raw-gadget + dummy_hcd emulating an Audio > Kontrol 1 (17cc:0815) with the EP1 bulk pair in interface 1: only > interface 0 was bound to snd-usb-caiaq and then unbound through sysfs > while the gadget flooded EP1 with EP1_CMD_READ_ERP replies. With no PCM > stream running the window is very short and was only hit by stalling > the unbinding CPU with a kgdb breakpoint at > snd_usb_caiaq_audio_disconnect(). With the fix applied, the same test > runs clean. > > BUG: KASAN: slab-use-after-free in input_event+0x3a/0xc0 > Read of size 8 at addr ffff8880151a4028 by task sh/118 > > Call Trace: > > input_event+0x3a/0xc0 > snd_usb_caiaq_input_dispatch+0xab2/0xf00 > usb_ep1_command_reply_dispatch+0x1f3/0x580 > __usb_hcd_giveback_urb+0x246/0x400 > dummy_timer+0x1415/0x3380 > __hrtimer_run_queues+0x39d/0x800 > hrtimer_run_softirq+0x187/0x2d0 > handle_softirqs+0x1ff/0x930 > __irq_exit_rcu+0x15b/0x210 > irq_exit_rcu+0xe/0x20 > sysvec_apic_timer_interrupt+0x81/0xb0 > > > asm_sysvec_apic_timer_interrupt+0x1a/0x20 > RIP: 0010:snd_usb_caiaq_audio_disconnect+0x0/0x70 > snd_disconnect+0x81/0x110 > usb_unbind_interface+0x1a0/0x860 > device_release_driver_internal+0x2c5/0x470 > unbind_store+0xde/0x100 > > > Allocated by task 80: > input_allocate_device+0x47/0x340 > snd_usb_caiaq_input_init+0x4c/0x1ac0 > snd_probe+0xab3/0x1160 > usb_probe_interface+0x2ea/0x810 > > Freed by task 118: > kfree+0x1ea/0x5c0 > input_dev_release+0xab/0xd0 > device_release+0xcf/0x250 > kobject_put+0x169/0x320 > snd_disconnect+0x79/0x110 > usb_unbind_interface+0x1a0/0x860 > > Fixes: b04dcbb7f7b1 ("ALSA: caiaq: Use snd_card_free_when_closed() at disconnection") > Cc: stable@vger.kernel.org > Signed-off-by: Sergei Nizovtsev > Assisted-by: Claude:claude-opus-4-8 Applied now. Thanks. Takashi