From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp105.ord1d.emailsrvr.com (smtp105.ord1d.emailsrvr.com [184.106.54.105]) (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 26F182E093B for ; Tue, 22 Jul 2025 13:06:46 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=184.106.54.105 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753189609; cv=none; b=FQzUy6rNBT65eajdIZPHLDDOziZzfHGqN5McapRlh87+d66C+ff1TeYOQNf+XGSVWyErlPaOLBnt5Nv/tm8s+M+TY+fmP6OFKho6QDqyqsADxlvtYyDzE8T2p5whCzlFKXVcB3PB4ViaEm0zoxB9uvG5aDxT7n+JOXVAu/LYw1w= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753189609; c=relaxed/simple; bh=LmWePo/3g77m2n8B1sY0JODJjFc3+XgNyjRmx2rI9LI=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=kpg797KSBTZwiJAUU1Wk4cqUowM0yP1bnQNM83HWaC+/Yn3Y746kWrr/p0n15cMAwhxyZkuS+huYL/PINKVVBAysbfNQ4sC5Zpkzw/2sLbIg9JT8PyKMyS3pQAx6E4L7LoXg3dcz05I52zIi6FYz7gaBelLUiy+VWmwAsagYTC4= 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=If1u89Gn; arc=none smtp.client-ip=184.106.54.105 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="If1u89Gn" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=mev.co.uk; s=20221208-6x11dpa4; t=1753188448; bh=LmWePo/3g77m2n8B1sY0JODJjFc3+XgNyjRmx2rI9LI=; h=Date:From:To:Subject:From; b=If1u89Gnq+gm+JToR1Ykvh9OkcZrAgVr/HqtOUsThjGgMEF9CFCSu6h0n8MoMXzYz YzlLk99shauXN7a7d05Ve6CAkkTGVa1r+ZmWG8S71xmHEujBvEgqYkhRJHjbDC8N1B lW+0b0f3abEWAZk0rUSHiWqFl547c7QKwIRRe2QE= X-Auth-ID: abbotti@mev.co.uk Received: by smtp14.relay.ord1d.emailsrvr.com (Authenticated sender: abbotti-AT-mev.co.uk) with ESMTPSA id 3F18540434; Tue, 22 Jul 2025 08:47:27 -0400 (EDT) Date: Tue, 22 Jul 2025 13:47:24 +0100 From: Ian Abbott 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 Subject: Re: [syzbot] [io-uring?] KASAN: slab-use-after-free Read in io_poll_remove_entries Message-ID: <20250722134724.6671e45b@ian-deb> In-Reply-To: References: <687bd5fe.a70a0220.693ce.0091.GAE@google.com> <9385a1a6-8c10-4eb5-9ab9-87aaeb6a7766@kernel.dk> Organization: MEV Ltd. X-Mailer: Claws Mail 4.3.1 (GTK 3.24.49; x86_64-pc-linux-gnu) 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-Transfer-Encoding: 7bit X-Classification-ID: 78e0694b-dd1b-4ff9-93c3-ba40d118cbd3-1-1 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. Something like this: diff --git a/drivers/comedi/comedi_fops.c b/drivers/comedi/comedi_fops.c index 3383a7ce27ff..a0048510fc40 100644 --- a/drivers/comedi/comedi_fops.c +++ b/drivers/comedi/comedi_fops.c @@ -787,6 +787,7 @@ static int is_device_busy(struct comedi_device *dev) struct comedi_subdevice *s; int i; + lockdep_assert_held_write(&dev->attach_lock); lockdep_assert_held(&dev->mutex); if (!dev->attached) return 0; @@ -795,7 +796,12 @@ static int is_device_busy(struct comedi_device *dev) s = &dev->subdevices[i]; if (s->busy) return 1; - if (s->async && comedi_buf_is_mmapped(s)) + if (!s->async) + continue; + if (comedi_buf_is_mmapped(s)) + return 1; + /* There may be transient active polls. */ + if (waitqueue_active(&s->async->wait_head)) return 1; } @@ -825,15 +831,22 @@ static int do_devconfig_ioctl(struct comedi_device *dev, return -EPERM; if (!arg) { - if (is_device_busy(dev)) - return -EBUSY; + int rc = 0; + if (dev->attached) { - struct module *driver_module = dev->driver->module; + down_write(&dev->attach_lock); + if (is_device_busy(dev)) { + rc = -EBUSY; + } else { + struct module *driver_module = + dev->driver->module; - comedi_device_detach(dev); - module_put(driver_module); + comedi_device_detach_locked(dev); + module_put(driver_module); + } + up_write(&dev->attach_lock); } - return 0; + return rc; } if (copy_from_user(&it, arg, sizeof(it))) diff --git a/drivers/comedi/comedi_internal.h b/drivers/comedi/comedi_internal.h index 9b3631a654c8..cf10ba016ebc 100644 --- a/drivers/comedi/comedi_internal.h +++ b/drivers/comedi/comedi_internal.h @@ -50,6 +50,7 @@ extern struct mutex comedi_drivers_list_lock; int insn_inval(struct comedi_device *dev, struct comedi_subdevice *s, struct comedi_insn *insn, unsigned int *data); +void comedi_device_detach_locked(struct comedi_device *dev); void comedi_device_detach(struct comedi_device *dev); int comedi_device_attach(struct comedi_device *dev, struct comedi_devconfig *it); diff --git a/drivers/comedi/drivers.c b/drivers/comedi/drivers.c index 376130bfba8a..f5c2ee271d0e 100644 --- a/drivers/comedi/drivers.c +++ b/drivers/comedi/drivers.c @@ -158,7 +158,7 @@ static void comedi_device_detach_cleanup(struct comedi_device *dev) int i; struct comedi_subdevice *s; - lockdep_assert_held(&dev->attach_lock); + lockdep_assert_held_write(&dev->attach_lock); lockdep_assert_held(&dev->mutex); if (dev->subdevices) { for (i = 0; i < dev->n_subdevices; i++) { @@ -196,16 +196,23 @@ static void comedi_device_detach_cleanup(struct comedi_device *dev) comedi_clear_hw_dev(dev); } -void comedi_device_detach(struct comedi_device *dev) +void comedi_device_detach_locked(struct comedi_device *dev) { + lockdep_assert_held_write(&dev->attach_lock); lockdep_assert_held(&dev->mutex); comedi_device_cancel_all(dev); - down_write(&dev->attach_lock); dev->attached = false; dev->detach_count++; if (dev->driver) dev->driver->detach(dev); comedi_device_detach_cleanup(dev); +} + +void comedi_device_detach(struct comedi_device *dev) +{ + lockdep_assert_held(&dev->mutex); + down_write(&dev->attach_lock); + comedi_device_detach_locked(dev); up_write(&dev->attach_lock); } -- -=( Ian Abbott || MEV Ltd. is a company )=- -=( registered in England & Wales. 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