Bug #400


KASAN: use-after-free Read in batadv_iv_ogm_queue_add

Added by Sven Eckelmann over 3 years ago. Updated almost 3 years ago.

Target version:
Start date:
Due date:
% Done:


Estimated time:




syzbot found the following crash on:

HEAD commit:    faeacb6d net: tap: clean up an indentation issue
git tree:       net
console output:
kernel config:
dashboard link:
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:

BUG: KASAN: use-after-free in memcpy include/linux/string.h:359 [inline]
BUG: KASAN: use-after-free in batadv_iv_ogm_aggregate_new  
net/batman-adv/bat_iv_ogm.c:544 [inline]
BUG: KASAN: use-after-free in batadv_iv_ogm_queue_add+0x31d/0x1120  
Read of size 24 at addr ffff888099112740 by task kworker/u4:2/2025

CPU: 1 PID: 2025 Comm: kworker/u4:2 Not tainted 5.3.0+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Workqueue: bat_events batadv_iv_send_outstanding_bat_ogm_packet
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+0x12/0x17 mm/kasan/common.c:618
  check_memory_region_inline mm/kasan/generic.c:185 [inline]
  check_memory_region+0x134/0x1a0 mm/kasan/generic.c:192
  memcpy+0x24/0x50 mm/kasan/common.c:122
  memcpy include/linux/string.h:359 [inline]
  batadv_iv_ogm_aggregate_new net/batman-adv/bat_iv_ogm.c:544 [inline]
  batadv_iv_ogm_queue_add+0x31d/0x1120 net/batman-adv/bat_iv_ogm.c:640
  batadv_iv_ogm_schedule+0x783/0xe50 net/batman-adv/bat_iv_ogm.c:797
  process_one_work+0x9af/0x1740 kernel/workqueue.c:2269
  worker_thread+0x98/0xe40 kernel/workqueue.c:2415
  kthread+0x361/0x430 kernel/kthread.c:255
  ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352

Allocated by task 9774:
  save_stack+0x23/0x90 mm/kasan/common.c:69
  set_track mm/kasan/common.c:77 [inline]
  __kasan_kmalloc mm/kasan/common.c:493 [inline]
  __kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:466
  kasan_kmalloc+0x9/0x10 mm/kasan/common.c:507
  kmem_cache_alloc_trace+0x158/0x790 mm/slab.c:3550
  kmalloc include/linux/slab.h:552 [inline]
  batadv_iv_ogm_iface_enable+0x123/0x320 net/batman-adv/bat_iv_ogm.c:201
  batadv_softif_slave_add+0x8f/0x100 net/batman-adv/soft-interface.c:892
  do_set_master net/core/rtnetlink.c:2369 [inline]
  do_set_master+0x1ca/0x230 net/core/rtnetlink.c:2343
  do_setlink+0xa85/0x3520 net/core/rtnetlink.c:2504
  rtnl_setlink+0x273/0x3d0 net/core/rtnetlink.c:2763
  rtnetlink_rcv_msg+0x463/0xb00 net/core/rtnetlink.c:5223
  netlink_rcv_skb+0x177/0x450 net/netlink/af_netlink.c:2477
  rtnetlink_rcv+0x1d/0x30 net/core/rtnetlink.c:5241
  netlink_unicast_kernel net/netlink/af_netlink.c:1302 [inline]
  netlink_unicast+0x531/0x710 net/netlink/af_netlink.c:1328
  netlink_sendmsg+0x8a5/0xd60 net/netlink/af_netlink.c:1917
  sock_sendmsg_nosec net/socket.c:637 [inline]
  sock_sendmsg+0xd7/0x130 net/socket.c:657
  sock_write_iter+0x27c/0x3e0 net/socket.c:989
  call_write_iter include/linux/fs.h:1880 [inline]
  do_iter_readv_writev+0x5f8/0x8f0 fs/read_write.c:693
  do_iter_write fs/read_write.c:970 [inline]
  do_iter_write+0x184/0x610 fs/read_write.c:951
  vfs_writev+0x1b3/0x2f0 fs/read_write.c:1015
  do_writev+0x15b/0x330 fs/read_write.c:1058
  __do_sys_writev fs/read_write.c:1131 [inline]
  __se_sys_writev fs/read_write.c:1128 [inline]
  __x64_sys_writev+0x75/0xb0 fs/read_write.c:1128
  do_syscall_64+0xfa/0x760 arch/x86/entry/common.c:290

Freed by task 7:
  save_stack+0x23/0x90 mm/kasan/common.c:69
  set_track mm/kasan/common.c:77 [inline]
  __kasan_slab_free+0x102/0x150 mm/kasan/common.c:455
  kasan_slab_free+0xe/0x10 mm/kasan/common.c:463
  __cache_free mm/slab.c:3425 [inline]
  kfree+0x10a/0x2c0 mm/slab.c:3756
  batadv_iv_ogm_iface_disable+0x39/0x80 net/batman-adv/bat_iv_ogm.c:220
  default_device_exit_batch+0x25c/0x410 net/core/dev.c:9830
  ops_exit_list.isra.0+0xfc/0x150 net/core/net_namespace.c:175
  cleanup_net+0x4e2/0xa60 net/core/net_namespace.c:594
  process_one_work+0x9af/0x1740 kernel/workqueue.c:2269
  worker_thread+0x98/0xe40 kernel/workqueue.c:2415
  kthread+0x361/0x430 kernel/kthread.c:255
  ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352

The buggy address belongs to the object at ffff888099112740
  which belongs to the cache kmalloc-32 of size 32
The buggy address is located 0 bytes inside of
  32-byte region [ffff888099112740, ffff888099112760)
The buggy address belongs to the page:
page:ffffea0002644480 refcount:1 mapcount:0 mapping:ffff8880aa4001c0  
flags: 0x1fffc0000000200(slab)
raw: 01fffc0000000200 ffffea0002995848 ffffea00029e8bc8 ffff8880aa4001c0
raw: ffff888099112fc1 ffff888099112000 000000010000003a 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
  ffff888099112600: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
  ffff888099112680: 00 fc fc fc fc fc fc fc fb fb fb fb fc fc fc fc
> ffff888099112700: 00 00 00 fc fc fc fc fc fb fb fb fb fc fc fc fc
  ffff888099112780: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
  ffff888099112800: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc

This bug is generated by a bot. It may contain errors.
See for more information about syzbot.
syzbot engineers can be reached at

syzbot will keep track of this bug report. See: for how to communicate with syzbot.
Actions #1

Updated by Sven Eckelmann over 3 years ago

If someone wants to rewrite the problematic places, here are the referenced positions in the code:

diff --git a/net/batman-adv/hard-interface.c b/net/batman-adv/hard-interface.c
index c90e4734..ad4245d6 100644
--- a/net/batman-adv/hard-interface.c
+++ b/net/batman-adv/hard-interface.c
@@ -872,6 +872,7 @@ void batadv_hardif_disable_interface(struct batadv_hard_iface *hard_iface,

+    // .disable frees hard_iface->bat_iv.ogm_buff without a lock
     hard_iface->if_status = BATADV_IF_NOT_IN_USE;

diff --git a/net/batman-adv/bat_iv_ogm.c b/net/batman-adv/bat_iv_ogm.c
index d78938e3..ab681473 100644
--- a/net/batman-adv/bat_iv_ogm.c
+++ b/net/batman-adv/bat_iv_ogm.c
@@ -541,6 +541,11 @@ static void batadv_iv_ogm_aggregate_new(const unsigned char *packet_buff,

     skb_buff = skb_put(forw_packet_aggr->skb, packet_len);
     forw_packet_aggr->packet_len = packet_len;
+    // here (and many other places) we try to access
+    // hard_iface->bat_iv.ogm_buff (behind packet_buff) without any
+    // kind of locking.
+    // so .disable could have freed hard_iface->bat_iv.ogm_buff in the
+    // meantime
     memcpy(skb_buff, packet_buff, packet_len);

     forw_packet_aggr->own = own_packet;

Functions which need to be fixed here for bat_iv:

  • batadv_iv_ogm_iface_enable
  • batadv_iv_ogm_iface_disable
  • batadv_iv_ogm_schedule (and subfunctions)

Also problematic are following functions which change the content of the OGM(2) while it might be accessed by the transmit function. So it should actually have been some kind of locking:

  • everything which calls batadv_tvlv_container_ogm_append
    • batadv_iv_ogm_schedule
    • batadv_v_ogm_send(?)
  • batadv_iv_ogm_primary_iface_set
  • batadv_iv_ogm_iface_update_mac
  • batadv_v_ogm_primary_iface_set(?)
Actions #2

Updated by Sven Eckelmann over 3 years ago

  • Status changed from New to Resolved
  • Target version set to 2019.4
Actions #3

Updated by Sven Eckelmann over 3 years ago

  • Status changed from Resolved to Closed
Actions #4

Updated by Sven Eckelmann almost 3 years ago

  • Description updated (diff)

Also available in: Atom PDF