[Bridge] KASAN: use-after-free Read in brnf_exit_net

Wed Jun 19 15:47:07 UTC 2019

Hello,

syzbot found the following crash on:

HEAD commit:    1c6b4050 Add linux-next specific files for 20190618
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=10126209a00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=3c614278993de456
dashboard link: https://syzkaller.appspot.com/bug?extid=43a3fa52c0d9c5c94f41
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=16291176a00000

The bug was bisected to:

commit b38d37a08ec4b19a9b9ec3a1ff5566781fcae1f1
Author: Stephen Rothwell <sfr at canb.auug.org.au>
Date:   Tue Jun 18 04:19:55 2019 +0000

     Merge remote-tracking branch 'drm/drm-next'

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=146f914ea00000
final crash:    https://syzkaller.appspot.com/x/report.txt?x=166f914ea00000
console output: https://syzkaller.appspot.com/x/log.txt?x=126f914ea00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+43a3fa52c0d9c5c94f41 at syzkaller.appspotmail.com
Fixes: b38d37a08ec4 ("Merge remote-tracking branch 'drm/drm-next'")

==================================================================
BUG: KASAN: use-after-free in br_netfilter_sysctl_exit_net  
net/bridge/br_netfilter_hooks.c:1121 [inline]
BUG: KASAN: use-after-free in brnf_exit_net+0x38c/0x3a0  
net/bridge/br_netfilter_hooks.c:1141
Read of size 8 at addr ffff8880a4078d60 by task kworker/u4:4/8749

CPU: 0 PID: 8749 Comm: kworker/u4:4 Not tainted 5.2.0-rc5-next-20190618 #17
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Workqueue: netns cleanup_net
Call Trace:
  __dump_stack lib/dump_stack.c:77 [inline]
  dump_stack+0x172/0x1f0 lib/dump_stack.c:113
  print_address_description.cold+0xd4/0x306 mm/kasan/report.c:351
  __kasan_report.cold+0x1b/0x36 mm/kasan/report.c:482
  kasan_report+0x12/0x20 mm/kasan/common.c:614
  __asan_report_load8_noabort+0x14/0x20 mm/kasan/generic_report.c:132
  br_netfilter_sysctl_exit_net net/bridge/br_netfilter_hooks.c:1121 [inline]
  brnf_exit_net+0x38c/0x3a0 net/bridge/br_netfilter_hooks.c:1141
  ops_exit_list.isra.0+0xaa/0x150 net/core/net_namespace.c:154
  cleanup_net+0x3fb/0x960 net/core/net_namespace.c:553
  process_one_work+0x989/0x1790 kernel/workqueue.c:2269
  worker_thread+0x98/0xe40 kernel/workqueue.c:2415
  kthread+0x354/0x420 kernel/kthread.c:255
  ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352

Allocated by task 11374:
  save_stack+0x23/0x90 mm/kasan/common.c:71
  set_track mm/kasan/common.c:79 [inline]
  __kasan_kmalloc mm/kasan/common.c:489 [inline]
  __kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:462
  kasan_kmalloc+0x9/0x10 mm/kasan/common.c:503
  __do_kmalloc mm/slab.c:3645 [inline]
  __kmalloc+0x15c/0x740 mm/slab.c:3654
  kmalloc include/linux/slab.h:552 [inline]
  kzalloc include/linux/slab.h:743 [inline]
  __register_sysctl_table+0xc7/0xef0 fs/proc/proc_sysctl.c:1327
  register_net_sysctl+0x29/0x30 net/sysctl_net.c:121
  br_netfilter_sysctl_init_net net/bridge/br_netfilter_hooks.c:1105 [inline]
  brnf_init_net+0x379/0x6a0 net/bridge/br_netfilter_hooks.c:1126
  ops_init+0xb3/0x410 net/core/net_namespace.c:130
  setup_net+0x2d3/0x740 net/core/net_namespace.c:316
  copy_net_ns+0x1df/0x340 net/core/net_namespace.c:439
  create_new_namespaces+0x400/0x7b0 kernel/nsproxy.c:103
  unshare_nsproxy_namespaces+0xc2/0x200 kernel/nsproxy.c:202
  ksys_unshare+0x444/0x980 kernel/fork.c:2822
  __do_sys_unshare kernel/fork.c:2890 [inline]
  __se_sys_unshare kernel/fork.c:2888 [inline]
  __x64_sys_unshare+0x31/0x40 kernel/fork.c:2888
  do_syscall_64+0xfd/0x680 arch/x86/entry/common.c:301
  entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 9:
  save_stack+0x23/0x90 mm/kasan/common.c:71
  set_track mm/kasan/common.c:79 [inline]
  __kasan_slab_free+0x102/0x150 mm/kasan/common.c:451
  kasan_slab_free+0xe/0x10 mm/kasan/common.c:459
  __cache_free mm/slab.c:3417 [inline]
  kfree+0x10a/0x2c0 mm/slab.c:3746
  __rcu_reclaim kernel/rcu/rcu.h:215 [inline]
  rcu_do_batch kernel/rcu/tree.c:2092 [inline]
  invoke_rcu_callbacks kernel/rcu/tree.c:2310 [inline]
  rcu_core+0xcc7/0x1500 kernel/rcu/tree.c:2291
  __do_softirq+0x25c/0x94c kernel/softirq.c:292

The buggy address belongs to the object at ffff8880a4078d40
  which belongs to the cache kmalloc-512 of size 512
The buggy address is located 32 bytes inside of
  512-byte region [ffff8880a4078d40, ffff8880a4078f40)
The buggy address belongs to the page:
page:ffffea0002901e00 refcount:1 mapcount:0 mapping:ffff8880aa400a80  
index:0xffff8880a40785c0
flags: 0x1fffc0000000200(slab)
raw: 01fffc0000000200 ffffea0001d636c8 ffffea0001b07308 ffff8880aa400a80
raw: ffff8880a40785c0 ffff8880a40780c0 0000000100000004 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
  ffff8880a4078c00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
  ffff8880a4078c80: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
> ffff8880a4078d00: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
                                                        ^
  ffff8880a4078d80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
  ffff8880a4078e00: 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.
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