On Fri, Apr 19, 2019 at 07:36:05AM -0700, syzbot wrote: > Hello, > > syzbot found the following crash on: > > HEAD commit: d34f9519 usb-fuzzer: main usb gadget fuzzer driver > git tree: https://github.com/google/kasan/tree/usb-fuzzer > console output: https://syzkaller.appspot.com/x/log.txt?x=125bbb5b200000 > kernel config: https://syzkaller.appspot.com/x/.config?x=c73d1bb5aeaeae20 > dashboard link: https://syzkaller.appspot.com/bug?extid=c025d34b8eaa54c571b8 > compiler: gcc (GCC) 9.0.0 20181231 (experimental) > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1513ac1d200000 > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=13555c1d200000 > > IMPORTANT: if you fix the bug, please add the following tag to the commit: > Reported-by: syzbot+c025d34b8eaa54c571b8@xxxxxxxxxxxxxxxxxxxxxxxxx > > em28xx 1-1:5.176: failed to create media graph > em28xx 1-1:5.176: V4L2 device video32 deregistered > em28xx 1-1:5.176: Binding DVB extension > ================================================================== > em28xx 1-1:5.176: no endpoint for DVB mode and transfer type 0 > BUG: KASAN: use-after-free in v4l2_fh_init+0x24c/0x290 > drivers/media/v4l2-core/v4l2-fh.c:33 > Read of size 8 at addr ffff8880a4f149d0 by task v4l_id/5313 > > CPU: 1 PID: 5313 Comm: v4l_id Not tainted 5.1.0-rc5-319617-gd34f951 #4 > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS > Google 01/01/2011 > em28xx 1-1:5.176: failed to pre-allocate USB transfer buffers for DVB. > Call Trace: > __dump_stack lib/dump_stack.c:77 [inline] > dump_stack+0xe8/0x16e lib/dump_stack.c:113 > print_address_description+0x6c/0x236 mm/kasan/report.c:187 > em28xx 1-1:5.176: Registering input extension > kasan_report.cold+0x1a/0x3c mm/kasan/report.c:317 > v4l2_fh_init+0x24c/0x290 drivers/media/v4l2-core/v4l2-fh.c:33 > v4l2_fh_open+0x8d/0xd0 drivers/media/v4l2-core/v4l2-fh.c:71 > em28xx_v4l2_open+0x11f/0x470 drivers/media/usb/em28xx/em28xx-video.c:2184 > v4l2_open+0x1b6/0x360 drivers/media/v4l2-core/v4l2-dev.c:427 > chrdev_open+0x220/0x5d0 fs/char_dev.c:417 > do_dentry_open+0x49c/0x1130 fs/open.c:777 > do_last fs/namei.c:3416 [inline] > path_openat+0x147d/0x40b0 fs/namei.c:3533 > do_filp_open+0x1a6/0x280 fs/namei.c:3563 > do_sys_open+0x3c5/0x590 fs/open.c:1069 > do_syscall_64+0xcf/0x4f0 arch/x86/entry/common.c:290 > entry_SYSCALL_64_after_hwframe+0x49/0xbe > RIP: 0033:0x7fdb23b8d120 > Code: 48 8b 15 1b 4d 2b 00 f7 d8 64 89 02 83 c8 ff c3 90 90 90 90 90 90 90 > 90 90 90 83 3d d5 a4 2b 00 00 75 10 b8 02 00 00 00 0f 05 <48> 3d 01 f0 ff ff > 73 31 c3 48 83 ec 08 e8 5e 8c 01 00 48 89 04 24 > RSP: 002b:00007ffc1aebde18 EFLAGS: 00000246 ORIG_RAX: 0000000000000002 > RAX: ffffffffffffffda RBX: 00007ffc1aebdf78 RCX: 00007fdb23b8d120 > RDX: 00007fdb23e42138 RSI: 0000000000000000 RDI: 00007ffc1aebef17 > RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000 > R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000400884 > R13: 00007ffc1aebdf70 R14: 0000000000000000 R15: 0000000000000000 > > Allocated by task 12: > set_track mm/kasan/common.c:87 [inline] > __kasan_kmalloc mm/kasan/common.c:497 [inline] > __kasan_kmalloc.constprop.0+0xbf/0xd0 mm/kasan/common.c:470 > kmalloc include/linux/slab.h:547 [inline] > kzalloc include/linux/slab.h:742 [inline] > em28xx_v4l2_init drivers/media/usb/em28xx/em28xx-video.c:2563 [inline] > em28xx_v4l2_init.cold+0x93/0x3112 > drivers/media/usb/em28xx/em28xx-video.c:2541 > em28xx_init_extension+0x13a/0x200 > drivers/media/usb/em28xx/em28xx-core.c:1128 > request_module_async+0x62/0x70 drivers/media/usb/em28xx/em28xx-cards.c:3300 > process_one_work+0x90f/0x1580 kernel/workqueue.c:2269 > worker_thread+0x9b/0xe20 kernel/workqueue.c:2415 > kthread+0x313/0x420 kernel/kthread.c:253 > ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:352 > > Freed by task 12: > set_track mm/kasan/common.c:87 [inline] > __kasan_slab_free+0x130/0x180 mm/kasan/common.c:459 > slab_free_hook mm/slub.c:1429 [inline] > slab_free_freelist_hook+0x5e/0x140 mm/slub.c:1456 > slab_free mm/slub.c:3003 [inline] > kfree+0xce/0x280 mm/slub.c:3958 > em28xx_free_v4l2 drivers/media/usb/em28xx/em28xx-video.c:2149 [inline] > kref_put include/linux/kref.h:67 [inline] > em28xx_v4l2_init drivers/media/usb/em28xx/em28xx-video.c:2920 [inline] > em28xx_v4l2_init.cold+0x2cf/0x3112 > drivers/media/usb/em28xx/em28xx-video.c:2541 > em28xx_init_extension+0x13a/0x200 > drivers/media/usb/em28xx/em28xx-core.c:1128 > request_module_async+0x62/0x70 drivers/media/usb/em28xx/em28xx-cards.c:3300 > process_one_work+0x90f/0x1580 kernel/workqueue.c:2269 > worker_thread+0x9b/0xe20 kernel/workqueue.c:2415 > kthread+0x313/0x420 kernel/kthread.c:253 > ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:352 > > The buggy address belongs to the object at ffff8880a4f14200 > which belongs to the cache kmalloc-8k of size 8192 > The buggy address is located 2000 bytes inside of > 8192-byte region [ffff8880a4f14200, ffff8880a4f16200) > The buggy address belongs to the page: > page:ffffea000293c400 count:1 mapcount:0 mapping:ffff88812c3f4400 index:0x0 > compound_mapcount: 0 > flags: 0xfff00000010200(slab|head) > raw: 00fff00000010200 dead000000000100 dead000000000200 ffff88812c3f4400 > raw: 0000000000000000 0000000080030003 00000001ffffffff 0000000000000000 > page dumped because: kasan: bad access detected > > Memory state around the buggy address: > ffff8880a4f14880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb > ffff8880a4f14900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb > > ffff8880a4f14980: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb > ^ > ffff8880a4f14a00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb > ffff8880a4f14a80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb > ================================================================== > > > --- > This bug is generated by a bot. It may contain errors. > See https://goo.gl/tpsmEJ for more information about syzbot. > syzbot engineers can be reached at syzkaller@xxxxxxxxxxxxxxxx. > > syzbot will keep track of this bug report. See: > https://goo.gl/tpsmEJ#status for how to communicate with syzbot. > syzbot can test patches for this bug, for details see: > https://goo.gl/tpsmEJ#testing-patches in v4l2_open() calling video_get() has no effect when vdev is a nested struct inside some driver's struct (em28xx_v4l2 in this case), and referencing vdev again, after a call to vdev->fops->open(), might cause UAF if the driver's struct has already been freed the following patch fixes both syzbot issue with v4l2_fh_init() and side issue with v4l2_open() described above: https://syzkaller.appspot.com/text?tag=Patch&x=15fbba30500000 1. it adds check for already freed struct in em28xx_v4l2_open(), it fixes this syzbot UAF report about v4l2_fh_init(), but it moves UAF up to v4l2_open() 2. it delays freeing of em28xx_v4l2, hence allows v4l2_open() to safely reference vdev and exit without UAF fix for #2 does not look great, and it seems that proper fix would be changing em28xx driver and having vdev allocated separateley and not nested in struct em28xx_v4l2: struct video_device *vdev instead of: struct video_device vdev and having em28xx utilize video_device_release() instead of video_device_release_empty() any advice or hints in fixing this would be highly appreciated, tyvm!
