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Bug #404
openKCSAN: data-race in batadv_tt_local_add / batadv_tt_local_add
Start date:
11/08/2019
Due date:
% Done:
0%
Estimated time:
Description
The new KCSAN (concurrency sanitizer) reported a problem with the TT code: https://lists.open-mesh.org/mailman3/hyperkitty/list/b.a.t.m.a.n@lists.open-mesh.org/message/Z44URGZT3NKZP5273KQEMW27WHGNJEUP/
Hello, syzbot found the following crash on: HEAD commit: 05f22368 x86, kcsan: Enable KCSAN for x86 git tree: https://github.com/google/ktsan.git kcsan console output: https://syzkaller.appspot.com/x/log.txt?x=1195a0d4e00000 kernel config: https://syzkaller.appspot.com/x/.config?x=87d111955f40591f dashboard link: https://syzkaller.appspot.com/bug?extid=1d5dadec56d9e87f0aac 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: Reported-by: syzbot+1d5dadec56d9e87f0aac@syzkaller.appspotmail.com ================================================================== BUG: KCSAN: data-race in batadv_tt_local_add / batadv_tt_local_add write to 0xffff8880a8e19698 of 2 bytes by task 10064 on cpu 0: batadv_tt_local_add+0x21b/0x1020 net/batman-adv/translation-table.c:799 batadv_interface_tx+0x398/0xae0 net/batman-adv/soft-interface.c:249 __netdev_start_xmit include/linux/netdevice.h:4420 [inline] netdev_start_xmit include/linux/netdevice.h:4434 [inline] xmit_one net/core/dev.c:3280 [inline] dev_hard_start_xmit+0xef/0x430 net/core/dev.c:3296 __dev_queue_xmit+0x14c9/0x1b60 net/core/dev.c:3873 dev_queue_xmit+0x21/0x30 net/core/dev.c:3906 __bpf_tx_skb net/core/filter.c:2060 [inline] __bpf_redirect_common net/core/filter.c:2099 [inline] __bpf_redirect+0x4b4/0x710 net/core/filter.c:2106 ____bpf_clone_redirect net/core/filter.c:2139 [inline] bpf_clone_redirect+0x1a5/0x1f0 net/core/filter.c:2111 bpf_prog_bb15b996d00816f9+0x71c/0x1000 bpf_test_run+0x1c3/0x490 net/bpf/test_run.c:44 bpf_prog_test_run_skb+0x4da/0x840 net/bpf/test_run.c:310 bpf_prog_test_run kernel/bpf/syscall.c:2108 [inline] __do_sys_bpf+0x1664/0x2b90 kernel/bpf/syscall.c:2884 __se_sys_bpf kernel/bpf/syscall.c:2825 [inline] __x64_sys_bpf+0x4c/0x60 kernel/bpf/syscall.c:2825 do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290 entry_SYSCALL_64_after_hwframe+0x44/0xa9 read to 0xffff8880a8e19698 of 2 bytes by task 9969 on cpu 1: batadv_tt_local_add+0x3d1/0x1020 net/batman-adv/translation-table.c:801 batadv_interface_tx+0x398/0xae0 net/batman-adv/soft-interface.c:249 __netdev_start_xmit include/linux/netdevice.h:4420 [inline] netdev_start_xmit include/linux/netdevice.h:4434 [inline] xmit_one net/core/dev.c:3280 [inline] dev_hard_start_xmit+0xef/0x430 net/core/dev.c:3296 __dev_queue_xmit+0x14c9/0x1b60 net/core/dev.c:3873 dev_queue_xmit+0x21/0x30 net/core/dev.c:3906 __bpf_tx_skb net/core/filter.c:2060 [inline] __bpf_redirect_common net/core/filter.c:2099 [inline] __bpf_redirect+0x4b4/0x710 net/core/filter.c:2106 ____bpf_clone_redirect net/core/filter.c:2139 [inline] bpf_clone_redirect+0x1a5/0x1f0 net/core/filter.c:2111 bpf_prog_bb15b996d00816f9+0x312/0x1000 bpf_test_run+0x1c3/0x490 net/bpf/test_run.c:44 bpf_prog_test_run_skb+0x4da/0x840 net/bpf/test_run.c:310 bpf_prog_test_run kernel/bpf/syscall.c:2108 [inline] __do_sys_bpf+0x1664/0x2b90 kernel/bpf/syscall.c:2884 __se_sys_bpf kernel/bpf/syscall.c:2825 [inline] __x64_sys_bpf+0x4c/0x60 kernel/bpf/syscall.c:2825 do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290 Reported by Kernel Concurrency Sanitizer on: CPU: 1 PID: 9969 Comm: syz-executor.2 Not tainted 5.4.0-rc3+ #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 ================================================================== --- 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@googlegroups.com. syzbot will keep track of this bug report. See: https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
Updated by Sven Eckelmann about 5 years ago
The relevant code is:
if (batadv_is_wifi_hardif(in_hardif))
tt_local->common.flags |= BATADV_TT_CLIENT_WIFI;
else
tt_local->common.flags &= ~BATADV_TT_CLIENT_WIFI;
So removing and adding this flag is not correctly protected with a method which prevents data races.
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