On 19/10/2020 00:01, Rustam Kovhaev wrote: > 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! > What should happen here is that the release() callback of 'struct v4l2_device v4l2_dev' is set. That release callback is called when the very last filehandle to any of the video device nodes is closed. I think a release callback that just calls 'kref_put(&v4l2->ref, em28xx_free_v4l2); kref_put(&dev->ref, em28xx_free_device);' should work. This driver predates that callback and it was never converted to use it. Regards, Hans
