From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp102.ord1d.emailsrvr.com (smtp102.ord1d.emailsrvr.com [184.106.54.102]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0406A265CAC for ; Tue, 22 Jul 2025 15:21:45 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=184.106.54.102 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753197708; cv=none; b=fXAm1Yj1LJm23LCJIp4dmCuz0f8q6Kh+jKXNfYSBsbmXpHqz/uv3Xk/uVzvZ5nipFqxZ05zRumY0S+3WzhOaxCTqVrKzKgL1mi81IIv/bXD5nheGeblgaLdCVGMHR9zA7Fqtp9tH4zVWwjLxBufH7/fIsTS/5rm/XslkvH+uu/c= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753197708; c=relaxed/simple; bh=LXkRdKrJDzRLcbSUZKbtZQa2pJ9LE+GAbhQbSfwrEVs=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=OKADPcQVT06dU9ya1xxmXG+2PIKyG3LxReObk843yjiQFZyqrOCuyU5IR0QUBfoTFsjHexHL1cNLQ7qmfb7mBk/lWfrKRcyznk6+LOtjxXtP82lPkhHR4KM76jTAojqziIN/ZNdMFCKsCNzKzSYAQDYTXtYR/j+LYl+/bhmSC1Q= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=mev.co.uk; spf=pass smtp.mailfrom=mev.co.uk; dkim=pass (1024-bit key) header.d=mev.co.uk header.i=@mev.co.uk header.b=TvmHL0js; arc=none smtp.client-ip=184.106.54.102 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=mev.co.uk Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=mev.co.uk Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=mev.co.uk header.i=@mev.co.uk header.b="TvmHL0js" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=mev.co.uk; s=20221208-6x11dpa4; t=1753193008; bh=LXkRdKrJDzRLcbSUZKbtZQa2pJ9LE+GAbhQbSfwrEVs=; h=Date:Subject:To:From:From; b=TvmHL0jsDXZlyJKFBkk9EGLh/y/5nkaWhYtXJlFM32jc6SH8veqb5RhxeWP7LFWMG IDMkVRzs0l3Ooqz8uFGV16fQ0Ma1jvlrrczUEnlEG9dvwM3A5SURPys3Nktqe61GIx vOyQfRzZR3eTjFqOaVnp41BrgptVMYWikxI2aK24= X-Auth-ID: abbotti@mev.co.uk Received: by smtp5.relay.ord1d.emailsrvr.com (Authenticated sender: abbotti-AT-mev.co.uk) with ESMTPSA id 3F516A0527; Tue, 22 Jul 2025 10:03:27 -0400 (EDT) Message-ID: <2ab129fa-802c-4df8-8aea-f17c81459eb9@mev.co.uk> Date: Tue, 22 Jul 2025 15:03:26 +0100 Precedence: bulk X-Mailing-List: io-uring@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [syzbot] [io-uring?] KASAN: slab-use-after-free Read in io_poll_remove_entries To: Jens Axboe Cc: syzbot , io-uring@vger.kernel.org, linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com, hsweeten@visionengravers.com, Greg Kroah-Hartman References: <687bd5fe.a70a0220.693ce.0091.GAE@google.com> <9385a1a6-8c10-4eb5-9ab9-87aaeb6a7766@kernel.dk> <20250722134724.6671e45b@ian-deb> <20250722143128.339d4462@ian-deb> Content-Language: en-GB From: Ian Abbott Organization: MEV Ltd. In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Classification-ID: 4edd9461-6f97-4e57-9b73-6224b71ceade-1-1 On 22/07/2025 14:50, Jens Axboe wrote: > On 7/22/25 7:31 AM, Ian Abbott wrote: >> On Tue, 22 Jul 2025 14:07:45 +0100 >> Ian Abbott wrote: >> >>> On 22/07/2025 14:00, Jens Axboe wrote: >>>> On 7/22/25 6:47 AM, Ian Abbott wrote: >>>>> On Sun, 20 Jul 2025 13:00:59 -0600 >>>>> Jens Axboe wrote: >>>>> >>>>>> On 7/20/25 12:49 PM, Jens Axboe wrote: >>>>>>> On 7/20/25 12:24 PM, Jens Axboe wrote: >>>>>>>> On 7/19/25 11:29 AM, syzbot wrote: >>>>>>>>> Hello, >>>>>>>>> >>>>>>>>> syzbot found the following issue on: >>>>>>>>> >>>>>>>>> HEAD commit: 4871b7cb27f4 Merge tag >>>>>>>>> 'v6.16-rc6-smb3-client-fixes' of gi.. git tree: upstream >>>>>>>>> console output: >>>>>>>>> https://syzkaller.appspot.com/x/log.txt?x=1288c38c580000 kernel >>>>>>>>> config: >>>>>>>>> https://syzkaller.appspot.com/x/.config?x=fa738a4418f051ee >>>>>>>>> dashboard link: >>>>>>>>> https://syzkaller.appspot.com/bug?extid=01523a0ae5600aef5895 >>>>>>>>> compiler: gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU >>>>>>>>> Binutils for Debian) 2.40 syz repro: >>>>>>>>> https://syzkaller.appspot.com/x/repro.syz?x=1688c38c580000 C >>>>>>>>> reproducer: >>>>>>>>> https://syzkaller.appspot.com/x/repro.c?x=166ed7d4580000 >>>>>>>>> >>>>>>>>> Downloadable assets: >>>>>>>>> disk image (non-bootable): >>>>>>>>> https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-4871b7cb.raw.xz >>>>>>>>> vmlinux: >>>>>>>>> https://storage.googleapis.com/syzbot-assets/4a9dea51d821/vmlinux-4871b7cb.xz >>>>>>>>> kernel image: >>>>>>>>> https://storage.googleapis.com/syzbot-assets/f96c723cdfe6/bzImage-4871b7cb.xz >>>>>>>>> >>>>>>>>> IMPORTANT: if you fix the issue, please add the following tag >>>>>>>>> to the commit: Reported-by: >>>>>>>>> syzbot+01523a0ae5600aef5895@syzkaller.appspotmail.com >>>>>>>>> >>>>>>>>> ================================================================== >>>>>>>>> BUG: KASAN: slab-use-after-free in __raw_spin_lock_irq >>>>>>>>> include/linux/spinlock_api_smp.h:119 [inline] BUG: KASAN: >>>>>>>>> slab-use-after-free in _raw_spin_lock_irq+0x36/0x50 >>>>>>>>> kernel/locking/spinlock.c:170 Read of size 1 at addr >>>>>>>>> ffff88803c6f42b0 by task kworker/2:2/1339 >>>>>>>>> >>>>>>>>> CPU: 2 UID: 0 PID: 1339 Comm: kworker/2:2 Not tainted >>>>>>>>> 6.16.0-rc6-syzkaller-00253-g4871b7cb27f4 #0 PREEMPT(full) >>>>>>>>> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS >>>>>>>>> 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014 Workqueue: events >>>>>>>>> io_fallback_req_func Call Trace: >>>>>>>>> __dump_stack lib/dump_stack.c:94 [inline] >>>>>>>>> dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120 >>>>>>>>> print_address_description mm/kasan/report.c:378 [inline] >>>>>>>>> print_report+0xcd/0x610 mm/kasan/report.c:480 >>>>>>>>> kasan_report+0xe0/0x110 mm/kasan/report.c:593 >>>>>>>>> __kasan_check_byte+0x36/0x50 mm/kasan/common.c:557 >>>>>>>>> kasan_check_byte include/linux/kasan.h:399 [inline] >>>>>>>>> lock_acquire kernel/locking/lockdep.c:5845 [inline] >>>>>>>>> lock_acquire+0xfc/0x350 kernel/locking/lockdep.c:5828 >>>>>>>>> __raw_spin_lock_irq include/linux/spinlock_api_smp.h:119 >>>>>>>>> [inline] _raw_spin_lock_irq+0x36/0x50 >>>>>>>>> kernel/locking/spinlock.c:170 spin_lock_irq >>>>>>>>> include/linux/spinlock.h:376 [inline] io_poll_remove_entry >>>>>>>>> io_uring/poll.c:146 [inline] >>>>>>>>> io_poll_remove_entries.part.0+0x14e/0x7e0 io_uring/poll.c:179 >>>>>>>>> io_poll_remove_entries io_uring/poll.c:159 [inline] >>>>>>>>> io_poll_task_func+0x4cd/0x1130 io_uring/poll.c:326 >>>>>>>>> io_fallback_req_func+0x1c7/0x6d0 io_uring/io_uring.c:259 >>>>>>>>> process_one_work+0x9cf/0x1b70 kernel/workqueue.c:3238 >>>>>>>>> process_scheduled_works kernel/workqueue.c:3321 [inline] >>>>>>>>> worker_thread+0x6c8/0xf10 kernel/workqueue.c:3402 >>>>>>>>> kthread+0x3c5/0x780 kernel/kthread.c:464 >>>>>>>>> ret_from_fork+0x5d4/0x6f0 arch/x86/kernel/process.c:148 >>>>>>>>> ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 >>>>>>>>> >>>>>>>>> >>>>>>>>> Allocated by task 6154: >>>>>>>>> kasan_save_stack+0x33/0x60 mm/kasan/common.c:47 >>>>>>>>> kasan_save_track+0x14/0x30 mm/kasan/common.c:68 >>>>>>>>> poison_kmalloc_redzone mm/kasan/common.c:377 [inline] >>>>>>>>> __kasan_kmalloc+0xaa/0xb0 mm/kasan/common.c:394 >>>>>>>>> kmalloc_noprof include/linux/slab.h:905 [inline] >>>>>>>>> kzalloc_noprof include/linux/slab.h:1039 [inline] >>>>>>>>> __comedi_device_postconfig_async drivers/comedi/drivers.c:664 >>>>>>>>> [inline] __comedi_device_postconfig >>>>>>>>> drivers/comedi/drivers.c:721 [inline] >>>>>>>>> comedi_device_postconfig+0x2cb/0xc80 >>>>>>>>> drivers/comedi/drivers.c:756 comedi_device_attach+0x3cf/0x900 >>>>>>>>> drivers/comedi/drivers.c:998 do_devconfig_ioctl+0x1a7/0x580 >>>>>>>>> drivers/comedi/comedi_fops.c:855 >>>>>>>>> comedi_unlocked_ioctl+0x15bb/0x2e90 >>>>>>>>> drivers/comedi/comedi_fops.c:2136 vfs_ioctl fs/ioctl.c:51 >>>>>>>>> [inline] __do_sys_ioctl fs/ioctl.c:907 [inline] __se_sys_ioctl >>>>>>>>> fs/ioctl.c:893 [inline] __x64_sys_ioctl+0x18e/0x210 >>>>>>>>> fs/ioctl.c:893 do_syscall_x64 arch/x86/entry/syscall_64.c:63 >>>>>>>>> [inline] do_syscall_64+0xcd/0x4c0 >>>>>>>>> arch/x86/entry/syscall_64.c:94 >>>>>>>>> entry_SYSCALL_64_after_hwframe+0x77/0x7f >>>>>>>>> >>>>>>>>> Freed by task 6156: >>>>>>>>> kasan_save_stack+0x33/0x60 mm/kasan/common.c:47 >>>>>>>>> kasan_save_track+0x14/0x30 mm/kasan/common.c:68 >>>>>>>>> kasan_save_free_info+0x3b/0x60 mm/kasan/generic.c:576 >>>>>>>>> poison_slab_object mm/kasan/common.c:247 [inline] >>>>>>>>> __kasan_slab_free+0x51/0x70 mm/kasan/common.c:264 >>>>>>>>> kasan_slab_free include/linux/kasan.h:233 [inline] >>>>>>>>> slab_free_hook mm/slub.c:2381 [inline] >>>>>>>>> slab_free mm/slub.c:4643 [inline] >>>>>>>>> kfree+0x2b4/0x4d0 mm/slub.c:4842 >>>>>>>>> comedi_device_detach_cleanup drivers/comedi/drivers.c:171 >>>>>>>>> [inline] comedi_device_detach+0x2a4/0x9e0 >>>>>>>>> drivers/comedi/drivers.c:208 do_devconfig_ioctl+0x46c/0x580 >>>>>>>>> drivers/comedi/comedi_fops.c:833 >>>>>>>>> comedi_unlocked_ioctl+0x15bb/0x2e90 >>>>>>>>> drivers/comedi/comedi_fops.c:2136 vfs_ioctl fs/ioctl.c:51 >>>>>>>>> [inline] __do_sys_ioctl fs/ioctl.c:907 [inline] __se_sys_ioctl >>>>>>>>> fs/ioctl.c:893 [inline] __x64_sys_ioctl+0x18e/0x210 >>>>>>>>> fs/ioctl.c:893 do_syscall_x64 arch/x86/entry/syscall_64.c:63 >>>>>>>>> [inline] do_syscall_64+0xcd/0x4c0 >>>>>>>>> arch/x86/entry/syscall_64.c:94 >>>>>>>>> entry_SYSCALL_64_after_hwframe+0x77/0x7f >>>>>>>> >>>>>>>> I took a quick look at this, and surely looks like a comedi bug. >>>>>>>> If you call the ioctl part (do_devconfig_ioctl()) with a NULL >>>>>>>> arg, it just does a detach and frees the device, regardless of >>>>>>>> whether anyone has it opened or not?! It's got some odd notion >>>>>>>> of checking whether it's busy or not. For this case, someone >>>>>>>> has a poll active on the device, yet it still happily frees it. >>>>>>>> >>>>>>>> CC'ing some folks, as this looks utterly broken. >>>>>>> >>>>>>> Case in point, I added: >>>>>>> >>>>>>> diff --git a/drivers/comedi/drivers.c b/drivers/comedi/drivers.c >>>>>>> index 376130bfba8a..4d5fde012558 100644 >>>>>>> --- a/drivers/comedi/drivers.c >>>>>>> +++ b/drivers/comedi/drivers.c >>>>>>> @@ -167,6 +167,7 @@ static void >>>>>>> comedi_device_detach_cleanup(struct comedi_device *dev) >>>>>>> kfree(s->private); comedi_free_subdevice_minor(s); >>>>>>> if (s->async) { >>>>>>> + >>>>>>> WARN_ON_ONCE(waitqueue_active(&s->async->wait_head)); >>>>>>> comedi_buf_alloc(dev, s, 0); kfree(s->async); >>>>>>> } >>>>>>> >>>>>>> and this is the first thing that triggers: >>>>>>> >>>>>>> WARNING: CPU: 1 PID: 807 at drivers/comedi/drivers.c:170 >>>>>>> comedi_device_detach+0x510/0x720 Modules linked in: >>>>>>> CPU: 1 UID: 0 PID: 807 Comm: comedi Not tainted >>>>>>> 6.16.0-rc6-00281-gf4a40a4282f4-dirty #1438 NONE Hardware name: >>>>>>> linux,dummy-virt (DT) pstate: 21400005 (nzCv daif +PAN -UAO -TCO >>>>>>> +DIT -SSBS BTYPE=--) pc : comedi_device_detach+0x510/0x720 >>>>>>> lr : comedi_device_detach+0x1dc/0x720 >>>>>>> sp : ffff80008aeb7880 >>>>>>> x29: ffff80008aeb7880 x28: 1fffe00020251205 x27: ffff000101289028 >>>>>>> x26: ffff00010578a000 x25: ffff000101289000 x24: 0000000000000007 >>>>>>> x23: 1fffe00020af1437 x22: 1fffe00020af1438 x21: 0000000000000000 >>>>>>> x20: 0000000000000000 x19: dfff800000000000 x18: ffff0000db102ec0 >>>>>>> x17: ffff80008208e6dc x16: ffff80008362e120 x15: ffff800080a47c1c >>>>>>> x14: ffff8000826f5aec x13: ffff8000836a0cc4 x12: ffff700010adcd15 >>>>>>> x11: 1ffff00010adcd14 x10: ffff700010adcd14 x9 : ffff8000836a105c >>>>>>> x8 : ffff800085bc0cc0 x7 : ffff00000b035b50 x6 : 0000000000000000 >>>>>>> x5 : 0000000000000000 x4 : ffff800080960e08 x3 : 0000000000000001 >>>>>>> x2 : ffff00000b4bf930 x1 : 0000000000000000 x0 : ffff0000d7e2b0d8 >>>>>>> Call trace: >>>>>>> comedi_device_detach+0x510/0x720 (P) >>>>>>> do_devconfig_ioctl+0x37c/0x4b8 >>>>>>> comedi_unlocked_ioctl+0x33c/0x2bd8 >>>>>>> __arm64_sys_ioctl+0x124/0x1a0 >>>>>>> invoke_syscall.constprop.0+0x60/0x2a0 >>>>>>> el0_svc_common.constprop.0+0x148/0x240 >>>>>>> do_el0_svc+0x40/0x60 >>>>>>> el0_svc+0x44/0xe0 >>>>>>> el0t_64_sync_handler+0x104/0x130 >>>>>>> el0t_64_sync+0x170/0x178 >>>>>>> >>>>>>> Not sure what the right fix for comedi is here, it'd probably be >>>>>>> at least somewhat saner if it only allowed removal of the device >>>>>>> when the ref count would be 1 (for the ioctl itself). Just >>>>>>> ignoring the file ref and allowing blanket removal seems highly >>>>>>> suspicious / broken. >>>>>>> >>>>>>> As there's no comedi subsystem in syzbot, moving it to kernel: >>>>>>> >>>>>>> #syz set subsystems: kernel >>>>>> >>>>>> Something like the below may help, at least it'll tell us the >>>>>> device is busy if there's a poll active on it. >>>>>> >>>>>> #syz test: >>>>>> git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git >>>>>> master >>>>>> >>>>>> >>>>>> diff --git a/drivers/comedi/comedi_fops.c >>>>>> b/drivers/comedi/comedi_fops.c index 3383a7ce27ff..ea96bc4b818e >>>>>> 100644 --- a/drivers/comedi/comedi_fops.c >>>>>> +++ b/drivers/comedi/comedi_fops.c >>>>>> @@ -785,21 +785,31 @@ void comedi_device_cancel_all(struct >>>>>> comedi_device *dev) static int is_device_busy(struct comedi_device >>>>>> *dev) { >>>>>> struct comedi_subdevice *s; >>>>>> - int i; >>>>>> + int i, is_busy = 0; >>>>>> >>>>>> lockdep_assert_held(&dev->mutex); >>>>>> if (!dev->attached) >>>>>> return 0; >>>>>> >>>>>> + /* prevent new polls */ >>>>>> + down_write(&dev->attach_lock); >>>>>> + >>>>>> for (i = 0; i < dev->n_subdevices; i++) { >>>>>> s = &dev->subdevices[i]; >>>>>> - if (s->busy) >>>>>> - return 1; >>>>>> - if (s->async && comedi_buf_is_mmapped(s)) >>>>>> - return 1; >>>>>> + if (s->busy) { >>>>>> + is_busy = 1; >>>>>> + break; >>>>>> + } >>>>>> + if (!s->async) >>>>>> + continue; >>>>>> + if (comedi_buf_is_mmapped(s) || >>>>>> + waitqueue_active(&s->async->wait_head)) { >>>>>> + is_busy = 1; >>>>>> + break; >>>>>> + } >>>>>> } >>>>>> - >>>>>> - return 0; >>>>>> + up_write(&dev->attach_lock); >>>>>> + return is_busy; >>>>>> } >>>>>> >>>>>> /* >>>>>> >>>>> >>>>> Thanks for your investigation and initial fix. I think >>>>> dev->attach_lock needs to be write-locked before calling >>>>> is_device_busy() and released after comedi_device_detach() >>>>> (although that also write-locks it, so we need to refactor that). >>>>> Otherwise, someone could get added to the wait_head after >>>>> is_device_busy() returns. >>>> >>>> That's fine too, this is what my v2 addressed as well. I don't know >>>> comedi well enough so I was worried about having ->attach_lock held >>>> over comedi_device_cancel_all() -> do_cancel() -> s->cancel() as >>>> that appears to be a new pattern. If you know this is fine, then >>>> yes by all means, we should just hold ->attach_lock over the whole >>>> thing and not need a detaching state. >>> >>> I think it's fine. do_cancel() (and s->cancel()) do not use >>> attach_lock. >>> >>> Actually, I was thinking it might be safer just to move the >>> `wait_queue_head_t wait_head;` member out of `struct comedi_async` >>> and into `struct comedi_subdevice`, then it should not matter if >>> there are any transient poll_wait() callers waiting on it. >>> >> >> Moving wait_head out of struct comedi_async: > > Not sure that's going to help, surely the device is going away as well, > not just the async part? Yes, you're right. At least the subdevices are going away, which is just as bad as the async structure going away. -- -=( Ian Abbott || MEV Ltd. is a company )=- -=( registered in England & Wales. Regd. number: 02862268. )=- -=( Regd. addr.: S11 & 12 Building 67, Europa Business Park, )=- -=( Bird Hall Lane, STOCKPORT, SK3 0XA, UK. || www.mev.co.uk )=-