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Tue, 04 Aug 2026 18:34:32 -0700 (PDT) Received: from Mac.lan ([125.128.148.126]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-3903f61ef2esm472369a91.3.2026.08.04.18.34.30 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Tue, 04 Aug 2026 18:34:32 -0700 (PDT) From: Baul Lee To: perex@perex.cz, tiwai@suse.com Cc: linux-sound@vger.kernel.org, linux-kernel@vger.kernel.org, federico.kirschbaum@xbow.com, stable@vger.kernel.org, Baul Lee Subject: [PATCH] ALSA: bcd2000: clear the URB pointers on disconnect Date: Wed, 5 Aug 2026 10:34:28 +0900 Message-ID: <20260805013428.38204-1-baul.lee@xbow.com> X-Mailer: git-send-email 2.50.1 Precedence: bulk X-Mailing-List: linux-sound@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit bcd2000_free_usb_related_resources() frees both URBs and leaves the pointers behind: usb_kill_urb(bcd2k->midi_out_urb); usb_kill_urb(bcd2k->midi_in_urb); usb_free_urb(bcd2k->midi_out_urb); usb_free_urb(bcd2k->midi_in_urb); The rawmidi device outlives that call. A substream that is still open when the device is unplugged reaches bcd2000_midi_send() from the trigger path on close. That function writes to the freed URB and then hands it to the USB core: bcd2k->midi_out_urb->transfer_buffer_length = BUFSIZE; ... ret = usb_submit_urb(bcd2k->midi_out_urb, GFP_ATOMIC); usb_kill_urb() does not stop a later submission either, so a submit that races the disconnect can requeue the URB after it has been reaped. midi_in_urb is exposed the same way: bcd2000_input_complete() resubmits it from the completion handler. KASAN on 7.2.0-rc5 (arm64): BUG: KASAN: slab-use-after-free in bcd2000_midi_send [snd_bcd2000] Write of size 4 at addr ffff00001827d388 by task bpoc/168 __asan_store4 bcd2000_midi_send [snd_bcd2000] bcd2000_midi_output_trigger [snd_bcd2000] snd_rawmidi_kernel_write1 close_substream.part.0 Freed by task 168: usb_free_urb bcd2000_disconnect [snd_bcd2000] BUG: KASAN: slab-use-after-free in usb_submit_urb Read of size 8 at addr ffff00001827d3b8 by task bpoc/168 Clear both pointers after freeing and test them on the paths that can still run. Poison the URBs before freeing them: usb_poison_urb() waits for a running completion handler and rejects any later submission, so after it returns the input path is quiesced and only the rawmidi trigger path can still reach bcd2000_midi_send(). No unpoison is needed; the URBs are freed on the next line. Discovered by XBOW, triaged by Baul Lee Fixes: b47a22290d58 ("ALSA: MIDI driver for Behringer BCD2000 USB device") Reported-by: Federico Kirschbaum Reported-by: Baul Lee Cc: stable@vger.kernel.org Signed-off-by: Baul Lee --- sound/usb/bcd2000/bcd2000.c | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-) diff --git a/sound/usb/bcd2000/bcd2000.c b/sound/usb/bcd2000/bcd2000.c index bebb48cb9abc..c5c542d17ccc 100644 --- a/sound/usb/bcd2000/bcd2000.c +++ b/sound/usb/bcd2000/bcd2000.c @@ -134,6 +134,9 @@ static void bcd2000_midi_send(struct bcd2000 *bcd2k) if (!midi_out_substream) return; + if (!bcd2k->midi_out_urb) + return; + /* copy command prefix bytes */ memcpy(bcd2k->midi_out_buf, device_cmd_prefix, sizeof(device_cmd_prefix)); @@ -178,7 +181,7 @@ static int bcd2000_midi_output_close(struct snd_rawmidi_substream *substream) { struct bcd2000 *bcd2k = substream->rmidi->private_data; - if (bcd2k->midi_out_active) { + if (bcd2k->midi_out_active && bcd2k->midi_out_urb) { usb_kill_urb(bcd2k->midi_out_urb); bcd2k->midi_out_active = 0; } @@ -348,11 +351,13 @@ static int bcd2000_init_midi(struct bcd2000 *bcd2k) static void bcd2000_free_usb_related_resources(struct bcd2000 *bcd2k, struct usb_interface *interface) { - usb_kill_urb(bcd2k->midi_out_urb); - usb_kill_urb(bcd2k->midi_in_urb); + usb_poison_urb(bcd2k->midi_out_urb); + usb_poison_urb(bcd2k->midi_in_urb); usb_free_urb(bcd2k->midi_out_urb); usb_free_urb(bcd2k->midi_in_urb); + bcd2k->midi_out_urb = NULL; + bcd2k->midi_in_urb = NULL; if (bcd2k->intf) { usb_set_intfdata(bcd2k->intf, NULL); -- 2.50.1 (Apple Git-155)