From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 6F6711E87B; Tue, 22 Jul 2025 12:31:18 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753187478; cv=none; b=YrAHIVi3Yc3KJh9wOto/9ZCWrKA+FWgCqwcCV2EXakHkuko8LPDsO8JgTDFc9S6t7M5ZdPgnWBcuASlrMMsA3k5rEYsOYryPd9B0XZKdqgyELT4+i+eYYR5pcm1rxYorxauYdeRdffGyDply3+L3Etfqs0F4d3Xx7v/oo3mAKVY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753187478; c=relaxed/simple; bh=ABtNJph1Ot7UQD8+L8w4RAKpOj/RL2lPgoDex6fv8kw=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; 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PPxxVGFunQwE/P47qCriqXxQyCiGEMfuDptttgdo= Date: Tue, 22 Jul 2025 14:31:15 +0200 From: Greg Kroah-Hartman To: Jens Axboe Cc: syzbot , io-uring@vger.kernel.org, linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com, abbotti@mev.co.uk, hsweeten@visionengravers.com Subject: Re: [syzbot] [io-uring?] KASAN: slab-use-after-free Read in io_poll_remove_entries Message-ID: <2025072226-stadium-spearhead-63cb@gregkh> References: <687bd5fe.a70a0220.693ce.0091.GAE@google.com> <9385a1a6-8c10-4eb5-9ab9-87aaeb6a7766@kernel.dk> Precedence: bulk X-Mailing-List: io-uring@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Tue, Jul 22, 2025 at 06:21:50AM -0600, 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? Please do. Note, a bunch of comedi bugfixes for syzbot-found-issues just langed in 6.16-rc7. I don't know if there's a way to trigger syzbot to re-run its check on that branch before you submit this? thanks, greg k-h