Date:   Fri, 25 Jun 2021 11:08:57 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Hillf Danton <hdanton@...a.com>
Cc:     syzbot <syzbot+19c5a4b75931e8d63aab@...kaller.appspotmail.com>,
        ezequiel@...labora.com, hverkuil-cisco@...all.nl,
        lijian@...ong.com, linux-kernel@...r.kernel.org,
        linux-media@...r.kernel.org, mchehab@...nel.org,
        sakari.ailus@...ux.intel.com, syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] KASAN: use-after-free Read in v4l2_ioctl (2)

On Fri, Jun 25, 2021 at 10:52 AM Hillf Danton <hdanton@...a.com> wrote:
>
> On Thu, 24 Jun 2021 21:53:15 -0700
> > syzbot found the following issue on:
> >
> > HEAD commit:    a1f92694 Add linux-next specific files for 20210518
> > git tree:       linux-next
> > console output: https://syzkaller.appspot.com/x/log.txt?x=12cb6184300000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=d612e75ffd53a6d3
> > dashboard link: https://syzkaller.appspot.com/bug?extid=19c5a4b75931e8d63aab
> > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=13f87f20300000
> > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=11f82d34300000
> >
> > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > Reported-by: syzbot+19c5a4b75931e8d63aab@...kaller.appspotmail.com
> >
> > ==================================================================
> > BUG: KASAN: use-after-free in v4l2_ioctl+0x1f1/0x250 drivers/media/v4l2-core/v4l2-dev.c:364
> > Read of size 8 at addr ffff88801dc54398 by task v4l_id/25000
> >
> > CPU: 0 PID: 25000 Comm: v4l_id Not tainted 5.13.0-rc2-next-20210518-syzkaller #0
> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> > Call Trace:
> >  __dump_stack lib/dump_stack.c:88 [inline]
> >  dump_stack_lvl+0x13e/0x1d6 lib/dump_stack.c:129
> >  print_address_description.constprop.0.cold+0x6c/0x309 mm/kasan/report.c:233
> >  __kasan_report mm/kasan/report.c:419 [inline]
> >  kasan_report.cold+0x83/0xdf mm/kasan/report.c:436
> >  v4l2_ioctl+0x1f1/0x250 drivers/media/v4l2-core/v4l2-dev.c:364
> >  vfs_ioctl fs/ioctl.c:51 [inline]
> >  __do_sys_ioctl fs/ioctl.c:1069 [inline]
> >  __se_sys_ioctl fs/ioctl.c:1055 [inline]
> >  __x64_sys_ioctl+0x193/0x200 fs/ioctl.c:1055
> >  do_syscall_64+0x31/0xb0 arch/x86/entry/common.c:47
> >  entry_SYSCALL_64_after_hwframe+0x44/0xae
> > RIP: 0033:0x7f30112bb017
> > Code: 00 00 00 48 8b 05 81 7e 2b 00 64 c7 00 26 00 00 00 48 c7 c0 ff ff ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 b8 10 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 51 7e 2b 00 f7 d8 64 89 01 48
> > RSP: 002b:00007ffcfc119d68 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
> > RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007f30112bb017
> > RDX: 00007ffcfc119d70 RSI: 0000000080685600 RDI: 0000000000000003
> > RBP: 0000000000000003 R08: 0000000000000000 R09: 0000000000000000
> > R10: 0000000000000002 R11: 0000000000000246 R12: 000055f2227cb8d0
> > R13: 00007ffcfc119ed0 R14: 0000000000000000 R15: 0000000000000000
> >
> > Allocated by task 12321:
> >  kasan_save_stack+0x1b/0x40 mm/kasan/common.c:38
> >  kasan_set_track mm/kasan/common.c:46 [inline]
> >  set_alloc_info mm/kasan/common.c:431 [inline]
> >  ____kasan_kmalloc mm/kasan/common.c:510 [inline]
> >  ____kasan_kmalloc mm/kasan/common.c:469 [inline]
> >  __kasan_kmalloc+0x9b/0xd0 mm/kasan/common.c:519
> >  kmalloc include/linux/slab.h:590 [inline]
> >  kzalloc include/linux/slab.h:720 [inline]
> >  stk_camera_probe+0x7d/0xc50 drivers/media/usb/stkwebcam/stk-webcam.c:1281
> >  usb_probe_interface+0x315/0x7f0 drivers/usb/core/driver.c:396
> >  really_probe+0x291/0xf60 drivers/base/dd.c:576
> >  driver_probe_device+0x298/0x410 drivers/base/dd.c:763
> >  __device_attach_driver+0x203/0x2c0 drivers/base/dd.c:870
> >  bus_for_each_drv+0x15f/0x1e0 drivers/base/bus.c:431
> >  __device_attach+0x228/0x4a0 drivers/base/dd.c:938
> >  bus_probe_device+0x1e4/0x290 drivers/base/bus.c:491
> >  device_add+0xbe0/0x2100 drivers/base/core.c:3320
> >  usb_set_configuration+0x113f/0x1910 drivers/usb/core/message.c:2164
> >  usb_generic_driver_probe+0xba/0x100 drivers/usb/core/generic.c:238
> >  usb_probe_device+0xd9/0x2c0 drivers/usb/core/driver.c:293
> >  really_probe+0x291/0xf60 drivers/base/dd.c:576
> >  driver_probe_device+0x298/0x410 drivers/base/dd.c:763
> >  __device_attach_driver+0x203/0x2c0 drivers/base/dd.c:870
> >  bus_for_each_drv+0x15f/0x1e0 drivers/base/bus.c:431
> >  __device_attach+0x228/0x4a0 drivers/base/dd.c:938
> >  bus_probe_device+0x1e4/0x290 drivers/base/bus.c:491
> >  device_add+0xbe0/0x2100 drivers/base/core.c:3320
> >  usb_new_device.cold+0x721/0x1058 drivers/usb/core/hub.c:2556
> >  hub_port_connect drivers/usb/core/hub.c:5276 [inline]
> >  hub_port_connect_change drivers/usb/core/hub.c:5416 [inline]
> >  port_event drivers/usb/core/hub.c:5562 [inline]
> >  hub_event+0x2357/0x4330 drivers/usb/core/hub.c:5644
> >  process_one_work+0x98d/0x1600 kernel/workqueue.c:2275
> >  worker_thread+0x64c/0x1120 kernel/workqueue.c:2421
> >  kthread+0x3b1/0x4a0 kernel/kthread.c:313
> >  ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294
> >
> > Freed by task 16814:
> >  kasan_save_stack+0x1b/0x40 mm/kasan/common.c:38
> >  kasan_set_track+0x1c/0x30 mm/kasan/common.c:46
> >  kasan_set_free_info+0x20/0x30 mm/kasan/generic.c:357
> >  ____kasan_slab_free mm/kasan/common.c:363 [inline]
> >  ____kasan_slab_free mm/kasan/common.c:328 [inline]
> >  __kasan_slab_free+0xfb/0x130 mm/kasan/common.c:371
> >  kasan_slab_free include/linux/kasan.h:212 [inline]
> >  slab_free_hook mm/slub.c:1623 [inline]
> >  slab_free_freelist_hook+0xdf/0x240 mm/slub.c:1648
> >  slab_free mm/slub.c:3208 [inline]
> >  kfree+0xeb/0x650 mm/slub.c:4274
> >  usb_unbind_interface+0x1d8/0x8d0 drivers/usb/core/driver.c:458
> >  __device_release_driver+0x3bd/0x6f0 drivers/base/dd.c:1181
> >  device_release_driver_internal drivers/base/dd.c:1212 [inline]
> >  device_release_driver+0x26/0x40 drivers/base/dd.c:1235
> >  bus_remove_device+0x2eb/0x5a0 drivers/base/bus.c:533
> >  device_del+0x502/0xd40 drivers/base/core.c:3508
> >  usb_disable_device+0x35b/0x7b0 drivers/usb/core/message.c:1413
> >  usb_disconnect.cold+0x27a/0x78e drivers/usb/core/hub.c:2219
> >  hub_port_connect drivers/usb/core/hub.c:5127 [inline]
> >  hub_port_connect_change drivers/usb/core/hub.c:5416 [inline]
> >  port_event drivers/usb/core/hub.c:5562 [inline]
> >  hub_event+0x1c9c/0x4330 drivers/usb/core/hub.c:5644
> >  process_one_work+0x98d/0x1600 kernel/workqueue.c:2275
> >  worker_thread+0x64c/0x1120 kernel/workqueue.c:2421
> >  kthread+0x3b1/0x4a0 kernel/kthread.c:313
> >  ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294
> >
> > The buggy address belongs to the object at ffff88801dc54000
> >  which belongs to the cache kmalloc-4k of size 4096
> > The buggy address is located 920 bytes inside of
> >  4096-byte region [ffff88801dc54000, ffff88801dc55000)
> > The buggy address belongs to the page:
> > page:ffffea0000771400 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x1dc50
> > head:ffffea0000771400 order:3 compound_mapcount:0 compound_pincount:0
> > flags: 0xfff00000010200(slab|head|node=0|zone=1|lastcpupid=0x7ff)
> > raw: 00fff00000010200 0000000000000000 0000000100000001 ffff888011042140
> > raw: 0000000000000000 0000000000040004 00000001ffffffff 0000000000000000
> > page dumped because: kasan: bad access detected
> > page_owner tracks the page as allocated
> > page last allocated via order 3, migratetype Unmovable, gfp_mask 0xd2040(__GFP_IO|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 11559, ts 1619924100847, free_ts 1619644095689
> >  prep_new_page mm/page_alloc.c:2377 [inline]
> >  get_page_from_freelist+0x125c/0x2ed0 mm/page_alloc.c:4038
> >  __alloc_pages+0x1b2/0x500 mm/page_alloc.c:5239
> >  alloc_pages+0x18c/0x2a0 mm/mempolicy.c:2272
> >  alloc_slab_page mm/slub.c:1686 [inline]
> >  allocate_slab+0x2c2/0x4c0 mm/slub.c:1826
> >  new_slab mm/slub.c:1889 [inline]
> >  new_slab_objects mm/slub.c:2635 [inline]
> >  ___slab_alloc+0x4ba/0x820 mm/slub.c:2798
> >  __slab_alloc.constprop.0+0xa7/0xf0 mm/slub.c:2838
> >  slab_alloc_node mm/slub.c:2920 [inline]
> >  slab_alloc mm/slub.c:2962 [inline]
> >  __kmalloc+0x312/0x330 mm/slub.c:4112
> >  kmalloc include/linux/slab.h:595 [inline]
> >  tomoyo_realpath_from_path+0xc3/0x620 security/tomoyo/realpath.c:254
> >  tomoyo_get_realpath security/tomoyo/file.c:151 [inline]
> >  tomoyo_path_perm+0x21b/0x400 security/tomoyo/file.c:822
> >  security_inode_getattr+0xcf/0x140 security/security.c:1332
> >  vfs_getattr fs/stat.c:139 [inline]
> >  vfs_statx+0x164/0x390 fs/stat.c:207
> >  vfs_fstatat fs/stat.c:225 [inline]
> >  vfs_lstat include/linux/fs.h:3384 [inline]
> >  __do_sys_newlstat+0x91/0x110 fs/stat.c:380
> >  do_syscall_64+0x31/0xb0 arch/x86/entry/common.c:47
> >  entry_SYSCALL_64_after_hwframe+0x44/0xae
> > page last free stack trace:
> >  reset_page_owner include/linux/page_owner.h:24 [inline]
> >  free_pages_prepare mm/page_alloc.c:1305 [inline]
> >  __free_pages_ok+0x4cb/0xf30 mm/page_alloc.c:1586
> >  qlink_free mm/kasan/quarantine.c:146 [inline]
> >  qlist_free_all+0x5a/0xc0 mm/kasan/quarantine.c:165
> >  kasan_quarantine_reduce+0x180/0x200 mm/kasan/quarantine.c:272
> >  __kasan_slab_alloc+0x8e/0xa0 mm/kasan/common.c:441
> >  kasan_slab_alloc include/linux/kasan.h:236 [inline]
> >  slab_post_alloc_hook mm/slab.h:512 [inline]
> >  slab_alloc_node mm/slub.c:2954 [inline]
> >  slab_alloc mm/slub.c:2962 [inline]
> >  kmem_cache_alloc+0x285/0x4a0 mm/slub.c:2967
> >  getname_flags.part.0+0x50/0x4f0 fs/namei.c:138
> >  getname_flags include/linux/audit.h:319 [inline]
> >  getname fs/namei.c:209 [inline]
> >  __do_sys_unlink fs/namei.c:4139 [inline]
> >  __se_sys_unlink fs/namei.c:4137 [inline]
> >  __x64_sys_unlink+0xb1/0x100 fs/namei.c:4137
> >  do_syscall_64+0x31/0xb0 arch/x86/entry/common.c:47
> >  entry_SYSCALL_64_after_hwframe+0x44/0xae
> >
> > Memory state around the buggy address:
> >  ffff88801dc54280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> >  ffff88801dc54300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> > >ffff88801dc54380: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> >                             ^
> >  ffff88801dc54400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> >  ffff88801dc54480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> > ==================================================================
>
> Given the uaf in the ioctl path, open count is needed and should be
> maintained by stk and is implemented in the diff below with mutex - it
> is locked at file open time, released at file release time and aquired
> at disconnect time.
>
> This can be a quick fix to the uaf, though, lights on why the video_get(vdev)
> in v4l2_open() fails to prevent stk camera from going home too early are
> welcome. Is it the fault on the driver side without an eye on open count?
>
> +++ x/drivers/media/usb/stkwebcam/stk-webcam.c
> @@ -624,8 +624,10 @@ static int v4l_stk_open(struct file *fp)
>                 dev->first_init = 0;
>
>         err = v4l2_fh_open(fp);
> -       if (!err)
> +       if (!err) {
>                 usb_autopm_get_interface(dev->interface);
> +               mutex_trylock(&dev->free_mutex);

I haven't read all of it, but doing mutex_trylock w/o checking the
return value looks very fishy. Can it ever be the right thing to
do?... E.g. the next line we unconditionally do mutex_unlock, are we
potentially unlocking a non-locked mutex?


> +       }
>         mutex_unlock(&dev->lock);
>         return err;
>  }
> @@ -633,6 +635,7 @@ static int v4l_stk_open(struct file *fp)
>  static int v4l_stk_release(struct file *fp)
>  {
>         struct stk_camera *dev = video_drvdata(fp);
> +       int rc;
>
>         mutex_lock(&dev->lock);
>         if (dev->owner == fp) {
> @@ -645,7 +648,9 @@ static int v4l_stk_release(struct file *
>
>         usb_autopm_put_interface(dev->interface);
>         mutex_unlock(&dev->lock);
> -       return v4l2_fh_release(fp);
> +       rc = v4l2_fh_release(fp);
> +       mutex_unlock(&dev->free_mutex);
> +       return rc;
>  }
>
>  static ssize_t stk_read(struct file *fp, char __user *buf,
> @@ -1306,6 +1311,7 @@ static int stk_camera_probe(struct usb_i
>
>         spin_lock_init(&dev->spinlock);
>         mutex_init(&dev->lock);
> +       mutex_init(&dev->free_mutex);
>         init_waitqueue_head(&dev->wait_frame);
>         dev->first_init = 1; /* webcam LED management */
>
> @@ -1385,6 +1391,8 @@ static void stk_camera_disconnect(struct
>         video_unregister_device(&dev->vdev);
>         v4l2_ctrl_handler_free(&dev->hdl);
>         v4l2_device_unregister(&dev->v4l2_dev);
> +       mutex_lock(&dev->free_mutex);
> +       mutex_unlock(&dev->free_mutex);
>         kfree(dev);
>  }

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