From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp98.iad3b.emailsrvr.com (smtp98.iad3b.emailsrvr.com [146.20.161.98]) (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 0A4B728C039 for ; Tue, 22 Jul 2025 13:06:48 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=146.20.161.98 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753189611; cv=none; b=tdNeReTwFa9UXUJ9weK3uHYEbYwC+AiZJUvrnjjisirD+TubzvgAhj2AwYRuCpXc1dYYQRG1k56g4fC+8IzF00WvuxEhv+OqeB0QZbGSsmZb5Shi37TYElRC/MPLS7VIOYEOesxC4ZlcFmQRlGvdPTyI0epTaxsQuQa5X3BkcwE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753189611; c=relaxed/simple; bh=Ti7WDj2VCaG6NyzBBiXIWzolXvvMYApNtHm4f66+knk=; h=Message-ID:Date:MIME-Version:Subject:To:References:From: In-Reply-To:Content-Type; b=FQw9qEqCa3lMsP5GPGgE4S68jmmvCtRi8ves8NsD4rccJau8iob29qAFTvJE6dn6oATitMPInm8VI441k1Zd6BMgesk3v+JUW1Hnw5cDCG1laviqRK49MAFKrcsua3YsOlfBnsN98sCvPxfUErWZqgjq2FbXhiS6NGuhvWP5KFg= 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=K9/RXUck; arc=none smtp.client-ip=146.20.161.98 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="K9/RXUck" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=mev.co.uk; s=20221208-6x11dpa4; t=1753187413; bh=Ti7WDj2VCaG6NyzBBiXIWzolXvvMYApNtHm4f66+knk=; h=Date:Subject:To:From:From; b=K9/RXUckuLIbE2yYpoS/d2O7TdVKfEGzKTZY9C5SsUdwJQR2gVG4QTz5v+7uvmgL3 aAof+BchOt2kJRE2jhmEbgocKHwLHtUjDyDuRXJl5Wbxo/odl0YFQCdjQ65ymZ+Y0E +TYMMx46P1cd2LTbb1De1J4gbqjV20k+bSVR+MR4= X-Auth-ID: abbotti@mev.co.uk Received: by smtp5.relay.iad3b.emailsrvr.com (Authenticated sender: abbotti-AT-mev.co.uk) with ESMTPSA id 2CCD2400C2; Tue, 22 Jul 2025 08:30:12 -0400 (EDT) Message-ID: <19daff9b-9b57-406b-8ee5-1d4ef5ba2855@mev.co.uk> Date: Tue, 22 Jul 2025 13:30:11 +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 , 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> 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: b117189b-c98a-46c7-860b-f3e6c0f5a7c0-1-1 On 22/07/2025 13:21, Jens Axboe wrote: > On 7/20/25 1:00 PM, 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; >> } >> >> /* > > Haven't heard anything back, so I guess I'll send it out as a patch? > Not yet, please. I'm working on it to close the remaining part of the race condition window. -- -=( 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 )=-