From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp83.iad3b.emailsrvr.com (smtp83.iad3b.emailsrvr.com [146.20.161.83]) (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 E4AA0289340 for ; Tue, 22 Jul 2025 13:46:59 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=146.20.161.83 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753192021; cv=none; b=nJxbZXOXRwn12j/VIjEuXqYqavwDme7GkxdKCTOWh65t6q3JD+YcSQv3kX/Am/tf2kC+M99vAZJ6qZ0jEXmnJicB9UcUIZRrm1WKoIjwsv9zbQS5lugZ7DS1wjTDOEnAg291jpHITAuLzt95MAJbnhIYEfeZ8GxHR7UQqwgALTk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753192021; c=relaxed/simple; bh=Ll2Qz/cfSyoMwJAmJ4JEPQQeh2moJJd1DKO/4bmFZYs=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=O1RrkpLx5eUARycDpLVYPHi/YgKS+xOd1Ufe6ubvga3Czs7odBDPt9i6fgDDl8kgcsIX08I/AfEEjHH+JqECJAQp7xz4vZYFMkZdDovgmtPCNxmy++4nK9s1udaMGN+od/4b62yTBE4cvsbnL0xPiZ5730lamPzXAZn4mLAnMF4= 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=zv4LhUcC; arc=none smtp.client-ip=146.20.161.83 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="zv4LhUcC" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=mev.co.uk; s=20221208-6x11dpa4; t=1753189667; bh=Ll2Qz/cfSyoMwJAmJ4JEPQQeh2moJJd1DKO/4bmFZYs=; h=Date:Subject:To:From:From; b=zv4LhUcCVdH6i6m6A+yOLhVWgHW5Ts48K7RV7w9eH2CjJID5lSpC0fkiqkbDvg+w7 tCo5NVV1l/V2ynVpgn5j1K/OXg3pDlHJ0HLPs+wGJkknJGqdZXnXSFmEJpRto7mqYv OKff3SLXoCHxdkG60zrng1t9K0LcjV/ZqBZ4h2s0= X-Auth-ID: abbotti@mev.co.uk Received: by smtp11.relay.iad3b.emailsrvr.com (Authenticated sender: abbotti-AT-mev.co.uk) with ESMTPSA id 10ACC40184; Tue, 22 Jul 2025 09:07:45 -0400 (EDT) Message-ID: Date: Tue, 22 Jul 2025 14:07:45 +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> 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: 90f4694a-d861-4781-b23a-4eaaafe75855-1-1 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. -- -=( 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 )=-