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[83.28.44.95]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-48448e80745sm12599197f8f.15.2026.09.03.02.24.21 (version=TLS1_2 cipher=AES128-SHA bits=128/128); Thu, 03 Sep 2026 02:24:22 -0700 (PDT) Date: Thu, 3 Sep 2026 11:24:17 +0200 From: Michal Pecio To: syzbot Cc: bolewara@gmail.com, devnull@kernel.org, gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org, linux-media@vger.kernel.org, linux-usb@vger.kernel.org, mchehab@kernel.org, syzkaller-bugs@googlegroups.com, Daniel Mack , Takashi Iwai , linux-sound@vger.kernel.org Subject: Re: [syzbot] [usb?] KASAN: slab-use-after-free Write in usb_free_urb Message-ID: <20260903112417.21b76017.michal.pecio@gmail.com> In-Reply-To: <6a97af8d.27a413cd.1e878c.0004.GAE@google.com> References: <6a6e9502.f794c993.27aeb.0018.GAE@google.com> <6a97af8d.27a413cd.1e878c.0004.GAE@google.com> Precedence: bulk X-Mailing-List: linux-media@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Tue, 01 Sep 2026 22:09:33 -0700, syzbot wrote: > syzbot has found a reproducer for the following issue on: > > HEAD commit: 786262be6048 Merge tag 'edac_updates_for_v7.3_rc2' of git:.. > git tree: upstream > console+strace: https://syzkaller.appspot.com/x/log.txt?x=12a28125580000 > kernel config: https://syzkaller.appspot.com/x/.config?x=b454dc6b1b7acd30 > dashboard link: https://syzkaller.appspot.com/bug?extid=832ce9fa3face1b7d44d > compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8 > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1735af79580000 > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=135b7f79580000 > > Downloadable assets: > disk image: https://storage.googleapis.com/syzbot-assets/c3e528ebf709/disk-786262be.raw.xz > vmlinux: https://storage.googleapis.com/syzbot-assets/46f3418d2828/vmlinux-786262be.xz > kernel image: https://storage.googleapis.com/syzbot-assets/60ab8a27c4f7/bzImage-786262be.xz > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > Reported-by: syzbot+832ce9fa3face1b7d44d@syzkaller.appspotmail.com > > usb 1-1: received EP1 urb->status = -2 > ================================================================== > BUG: KASAN: slab-use-after-free in instrument_atomic_read_write include/linux/instrumented.h:112 [inline] > BUG: KASAN: slab-use-after-free in atomic_fetch_sub_release include/linux/atomic/atomic-instrumented.h:400 [inline] > BUG: KASAN: slab-use-after-free in __refcount_sub_and_test include/linux/refcount.h:389 [inline] > BUG: KASAN: slab-use-after-free in __refcount_dec_and_test include/linux/refcount.h:432 [inline] > BUG: KASAN: slab-use-after-free in refcount_dec_and_test include/linux/refcount.h:450 [inline] > BUG: KASAN: slab-use-after-free in kref_put include/linux/kref.h:64 [inline] > BUG: KASAN: slab-use-after-free in usb_free_urb+0x24/0x120 drivers/usb/core/urb.c:96 > Write of size 4 at addr ffff88803cee1050 by task ktimers/1/29 > > CPU: 1 UID: 0 PID: 29 Comm: ktimers/1 Not tainted syzkaller #0 PREEMPT_{RT,(full)} > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026 > Call Trace: > > dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120 > print_address_description+0x55/0x1e0 mm/kasan/report.c:378 > print_report+0x58/0x70 mm/kasan/report.c:482 > kasan_report+0x117/0x150 mm/kasan/report.c:595 > check_region_inline mm/kasan/generic.c:-1 [inline] > kasan_check_range+0x264/0x2c0 mm/kasan/generic.c:200 > instrument_atomic_read_write include/linux/instrumented.h:112 [inline] > atomic_fetch_sub_release include/linux/atomic/atomic-instrumented.h:400 [inline] > __refcount_sub_and_test include/linux/refcount.h:389 [inline] > __refcount_dec_and_test include/linux/refcount.h:432 [inline] > refcount_dec_and_test include/linux/refcount.h:450 [inline] > kref_put include/linux/kref.h:64 [inline] > usb_free_urb+0x24/0x120 drivers/usb/core/urb.c:96 > dummy_timer+0xaac/0x4d50 drivers/usb/gadget/udc/dummy_hcd.c:2019 > __run_hrtimer kernel/time/hrtimer.c:2067 [inline] > __hrtimer_run_queues+0x3eb/0xaf0 kernel/time/hrtimer.c:2124 > hrtimer_run_softirq+0x1e1/0x2e0 kernel/time/hrtimer.c:2141 > handle_softirqs+0x1da/0x6d0 kernel/softirq.c:645 > __do_softirq kernel/softirq.c:679 [inline] > run_ktimerd+0x6a/0x100 kernel/softirq.c:1183 > smpboot_thread_fn+0x565/0xa70 kernel/smpboot.c:160 > kthread+0x38b/0x470 kernel/kthread.c:436 > ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158 > ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 > [Adding sound people] So what happens here is that USB core continues to use a URB after completion to implement things like usb_kill_urb(), so URBs are reference counted. Then core decrements the count - one more use. If a driver waits for completion or even usb_kill_urb() to return and then proceeds to free the URB's storage, this becomes a UAF. This driver embeds 2 URBs in its priv and does just that. A URB can only exist as an independent allocation, core will free it if upon finding zero reference count in such case. This is a mechanical conversion, untested. I don't have the HW. #syz test diff --git a/sound/usb/caiaq/device.c b/sound/usb/caiaq/device.c index a16e59248480..3587794207d4 100644 --- a/sound/usb/caiaq/device.c +++ b/sound/usb/caiaq/device.c @@ -192,8 +192,7 @@ static void usb_ep1_command_reply_dispatch (struct urb* urb) break; } - cdev->ep1_in_urb.actual_length = 0; - ret = usb_submit_urb(&cdev->ep1_in_urb, GFP_ATOMIC); + ret = usb_submit_urb(cdev->ep1_in_urb, GFP_ATOMIC); if (ret < 0) dev_err(dev, "unable to submit urb. OOM!?\n"); } @@ -403,6 +402,8 @@ static void card_free(struct snd_card *card) { struct snd_usb_caiaqdev *cdev = caiaqdev(card); + usb_free_urb(cdev->ep1_in_urb); + usb_free_urb(cdev->midi_out_urb); #ifdef CONFIG_SND_USB_CAIAQ_INPUT snd_usb_caiaq_input_free(cdev); #endif @@ -457,22 +458,24 @@ static int init_card(struct snd_usb_caiaqdev *cdev) return -EIO; } - usb_init_urb(&cdev->ep1_in_urb); - usb_init_urb(&cdev->midi_out_urb); + cdev->ep1_in_urb = usb_alloc_urb(0, GFP_KERNEL); + cdev->midi_out_urb = usb_alloc_urb(0, GFP_KERNEL); + if (!cdev->ep1_in_urb || !cdev->midi_out_urb) + return -ENOMEM; - usb_fill_bulk_urb(&cdev->ep1_in_urb, usb_dev, + usb_fill_bulk_urb(cdev->ep1_in_urb, usb_dev, usb_rcvbulkpipe(usb_dev, 0x1), cdev->ep1_in_buf, EP1_BUFSIZE, usb_ep1_command_reply_dispatch, cdev); - usb_fill_bulk_urb(&cdev->midi_out_urb, usb_dev, + usb_fill_bulk_urb(cdev->midi_out_urb, usb_dev, usb_sndbulkpipe(usb_dev, 0x1), cdev->midi_out_buf, EP1_BUFSIZE, snd_usb_caiaq_midi_output_done, cdev); /* sanity checks of EPs before actually submitting */ - if (usb_urb_ep_type_check(&cdev->ep1_in_urb) || - usb_urb_ep_type_check(&cdev->midi_out_urb)) { + if (usb_urb_ep_type_check(cdev->ep1_in_urb) || + usb_urb_ep_type_check(cdev->midi_out_urb)) { dev_err(dev, "invalid EPs\n"); return -EINVAL; } @@ -480,7 +483,7 @@ static int init_card(struct snd_usb_caiaqdev *cdev) init_waitqueue_head(&cdev->ep1_wait_queue); init_waitqueue_head(&cdev->prepare_wait_queue); - if (usb_submit_urb(&cdev->ep1_in_urb, GFP_KERNEL) != 0) + if (usb_submit_urb(cdev->ep1_in_urb, GFP_KERNEL) != 0) return -EIO; err = snd_usb_caiaq_send_command(cdev, EP1_CMD_GET_DEVICE_INFO, NULL, 0); @@ -530,7 +533,7 @@ static int init_card(struct snd_usb_caiaqdev *cdev) return 0; err_kill_urb: - usb_kill_urb(&cdev->ep1_in_urb); + usb_kill_urb(cdev->ep1_in_urb); return err; } @@ -576,8 +579,8 @@ static void snd_disconnect(struct usb_interface *intf) #endif snd_usb_caiaq_audio_disconnect(cdev); - usb_kill_urb(&cdev->ep1_in_urb); - usb_kill_urb(&cdev->midi_out_urb); + usb_kill_urb(cdev->ep1_in_urb); + usb_kill_urb(cdev->midi_out_urb); snd_card_free_when_closed(card); } diff --git a/sound/usb/caiaq/device.h b/sound/usb/caiaq/device.h index 743eb0387b5f..1c6f34693fa8 100644 --- a/sound/usb/caiaq/device.h +++ b/sound/usb/caiaq/device.h @@ -60,8 +60,8 @@ struct snd_usb_caiaq_cb_info; struct snd_usb_caiaqdev { struct snd_usb_audio chip; - struct urb ep1_in_urb; - struct urb midi_out_urb; + struct urb *ep1_in_urb; + struct urb *midi_out_urb; struct urb **data_urbs_in; struct urb **data_urbs_out; struct snd_usb_caiaq_cb_info *data_cb_info; diff --git a/sound/usb/caiaq/midi.c b/sound/usb/caiaq/midi.c index c656d0162432..18529484c8dc 100644 --- a/sound/usb/caiaq/midi.c +++ b/sound/usb/caiaq/midi.c @@ -43,7 +43,7 @@ static int snd_usb_caiaq_midi_output_close(struct snd_rawmidi_substream *substre { struct snd_usb_caiaqdev *cdev = substream->rmidi->private_data; if (cdev->midi_out_active) { - usb_kill_urb(&cdev->midi_out_urb); + usb_kill_urb(cdev->midi_out_urb); cdev->midi_out_active = 0; } return 0; @@ -64,9 +64,9 @@ static void snd_usb_caiaq_midi_send(struct snd_usb_caiaqdev *cdev, return; cdev->midi_out_buf[2] = len; - cdev->midi_out_urb.transfer_buffer_length = len+3; + cdev->midi_out_urb->transfer_buffer_length = len+3; - ret = usb_submit_urb(&cdev->midi_out_urb, GFP_ATOMIC); + ret = usb_submit_urb(cdev->midi_out_urb, GFP_ATOMIC); if (ret < 0) dev_err(dev, "snd_usb_caiaq_midi_send(%p): usb_submit_urb() failed,"