Re: KASAN: use-after-free Read in netdevice_event_work_handler

[Rustam Kovhaev]

On Thu, Jul 09, 2020 at 04:54:19PM -0700, syzbot wrote:
> Hello,
> 
> syzbot found the following crash on:
> 
> HEAD commit:    0bddd227 Documentation: update for gcc 4.9 requirement
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=1418afb7100000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=66ad203c2bb6d8b
> dashboard link: https://syzkaller.appspot.com/bug?extid=20b90969babe05609947
> compiler:       gcc (GCC) 10.1.0-syz 20200507
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12a8edff100000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=167d3bb7100000
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+20b90969babe05609947@xxxxxxxxxxxxxxxxxxxxxxxxx
> 
> ==================================================================
> BUG: KASAN: use-after-free in dev_put include/linux/netdevice.h:3853 [inline]
> BUG: KASAN: use-after-free in netdevice_event_work_handler+0x15b/0x1b0 drivers/infiniband/core/roce_gid_mgmt.c:627
> Read of size 8 at addr ffff88807b13e568 by task kworker/u4:0/7
> 
> CPU: 0 PID: 7 Comm: kworker/u4:0 Not tainted 5.8.0-rc4-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Workqueue: gid-cache-wq netdevice_event_work_handler
> Call Trace:
>  __dump_stack lib/dump_stack.c:77 [inline]
>  dump_stack+0x18f/0x20d lib/dump_stack.c:118
>  print_address_description.constprop.0.cold+0xae/0x436 mm/kasan/report.c:383
>  __kasan_report mm/kasan/report.c:513 [inline]
>  kasan_report.cold+0x1f/0x37 mm/kasan/report.c:530
>  dev_put include/linux/netdevice.h:3853 [inline]
>  netdevice_event_work_handler+0x15b/0x1b0 drivers/infiniband/core/roce_gid_mgmt.c:627
>  process_one_work+0x94c/0x1670 kernel/workqueue.c:2269
>  worker_thread+0x64c/0x1120 kernel/workqueue.c:2415
>  kthread+0x3b5/0x4a0 kernel/kthread.c:291
>  ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:293
> 
> Allocated by task 13061:
>  save_stack+0x1b/0x40 mm/kasan/common.c:48
>  set_track mm/kasan/common.c:56 [inline]
>  __kasan_kmalloc.constprop.0+0xc2/0xd0 mm/kasan/common.c:494
>  kmalloc_node include/linux/slab.h:578 [inline]
>  kvmalloc_node+0x61/0xf0 mm/util.c:574
>  kvmalloc include/linux/mm.h:753 [inline]
>  kvzalloc include/linux/mm.h:761 [inline]
>  alloc_netdev_mqs+0x97/0xdc0 net/core/dev.c:9938
>  __ip_tunnel_create+0x201/0x580 net/ipv4/ip_tunnel.c:254
>  ip_tunnel_init_net+0x32b/0x980 net/ipv4/ip_tunnel.c:1072
>  ops_init+0xaf/0x470 net/core/net_namespace.c:151
>  setup_net+0x2d8/0x850 net/core/net_namespace.c:341
>  copy_net_ns+0x2cf/0x5e0 net/core/net_namespace.c:482
>  create_new_namespaces+0x3f6/0xb10 kernel/nsproxy.c:110
>  unshare_nsproxy_namespaces+0xbd/0x1f0 kernel/nsproxy.c:231
>  ksys_unshare+0x36c/0x9a0 kernel/fork.c:2983
>  __do_sys_unshare kernel/fork.c:3051 [inline]
>  __se_sys_unshare kernel/fork.c:3049 [inline]
>  __x64_sys_unshare+0x2d/0x40 kernel/fork.c:3049
>  do_syscall_64+0x60/0xe0 arch/x86/entry/common.c:384
>  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> 
> Freed by task 13061:
>  save_stack+0x1b/0x40 mm/kasan/common.c:48
>  set_track mm/kasan/common.c:56 [inline]
>  kasan_set_free_info mm/kasan/common.c:316 [inline]
>  __kasan_slab_free+0xf5/0x140 mm/kasan/common.c:455
>  __cache_free mm/slab.c:3426 [inline]
>  kfree+0x103/0x2c0 mm/slab.c:3757
>  kvfree+0x42/0x50 mm/util.c:603
>  device_release+0x71/0x200 drivers/base/core.c:1559
>  kobject_cleanup lib/kobject.c:693 [inline]
>  kobject_release lib/kobject.c:722 [inline]
>  kref_put include/linux/kref.h:65 [inline]
>  kobject_put+0x1c0/0x270 lib/kobject.c:739
>  put_device+0x1b/0x30 drivers/base/core.c:2779
>  free_netdev+0x35d/0x480 net/core/dev.c:10054
>  __ip_tunnel_create+0x48f/0x580 net/ipv4/ip_tunnel.c:274
>  ip_tunnel_init_net+0x32b/0x980 net/ipv4/ip_tunnel.c:1072
>  ops_init+0xaf/0x470 net/core/net_namespace.c:151
>  setup_net+0x2d8/0x850 net/core/net_namespace.c:341
>  copy_net_ns+0x2cf/0x5e0 net/core/net_namespace.c:482
>  create_new_namespaces+0x3f6/0xb10 kernel/nsproxy.c:110
>  unshare_nsproxy_namespaces+0xbd/0x1f0 kernel/nsproxy.c:231
>  ksys_unshare+0x36c/0x9a0 kernel/fork.c:2983
>  __do_sys_unshare kernel/fork.c:3051 [inline]
>  __se_sys_unshare kernel/fork.c:3049 [inline]
>  __x64_sys_unshare+0x2d/0x40 kernel/fork.c:3049
>  do_syscall_64+0x60/0xe0 arch/x86/entry/common.c:384
>  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> 
> The buggy address belongs to the object at ffff88807b13e000
>  which belongs to the cache kmalloc-4k of size 4096
> The buggy address is located 1384 bytes inside of
>  4096-byte region [ffff88807b13e000, ffff88807b13f000)
> The buggy address belongs to the page:
> page:ffffea0001ec4f80 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 head:ffffea0001ec4f80 order:1 compound_mapcount:0
> flags: 0xfffe0000010200(slab|head)
> raw: 00fffe0000010200 ffffea0001ecce88 ffffea0001987988 ffff8880aa002000
> raw: 0000000000000000 ffff88807b13e000 0000000100000001 0000000000000000
> page dumped because: kasan: bad access detected
> 
> Memory state around the buggy address:
>  ffff88807b13e400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ffff88807b13e480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> >ffff88807b13e500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>                                                           ^
>  ffff88807b13e580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ffff88807b13e600: 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@xxxxxxxxxxxxxxxxx
> 
> 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

IB roce driver receives NETDEV_UNREGISTER event, calls dev_hold() and
schedules work item to execute, and before wq gets a chance to complete
it, we return to ip_tunnel.c:274 and call free_netdev(), and then later
we get UAF when scheduled function references already freed net_device

i added verbose logging to ip_tunnel.c to see pcpu_refcnt:
+       pr_info("about to free_netdev(dev) dev->pcpu_refcnt %d", netdev_refcnt_read(dev));

and got the following:
[  410.220127][ T2944] ip_tunnel: about to free_netdev(dev) dev->pcpu_refcnt 8

i tried to make IB roce driver flush wq and work item, but i ran into
lockdep issues
also tried to modify dev core and call netdev_wait_allrefs() but ran
into rntl deadlocks

any hints or help in fixing this would be appreciated, thank you!