Hi Abhishek, On Mon, Feb 24, 2020 at 11:33 AM Abhishek Pandit-Subedi <abhishekpandit@xxxxxxxxxxxx> wrote: > > (Resent in plain text; sorry for double send) > > I took a brief look at this error and uncovered that 6lowpan uses zero > locks when using l2cap (should be using the channel lock). > > It seems like it would be better just to convert its direct use of > l2cap channel into using an l2cap socket. I recall having some thought on that, I think having a socket like RFCOMM does would be better but I don't remember why I haven't follow-up on that, well we wanted to discontinue the bt specific 6lowpan on the kernel side though. > On Mon, Feb 24, 2020 at 12:28 AM syzbot > <syzbot+198362c76088d1515529@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote: > > > > Hello, > > > > syzbot found the following crash on: > > > > HEAD commit: bee46b30 Add linux-next specific files for 20200221 > > git tree: linux-next > > console output: https://syzkaller.appspot.com/x/log.txt?x=1244ea7ee00000 > > kernel config: https://syzkaller.appspot.com/x/.config?x=10693880b4976691 > > dashboard link: https://syzkaller.appspot.com/bug?extid=198362c76088d1515529 > > compiler: gcc (GCC) 9.0.0 20181231 (experimental) > > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=160a03d9e00000 > > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=10f8e1dde00000 > > > > Bisection is inconclusive: the bug happens on the oldest tested release. > > > > bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=13f03a7ee00000 > > final crash: https://syzkaller.appspot.com/x/report.txt?x=10083a7ee00000 > > console output: https://syzkaller.appspot.com/x/log.txt?x=17f03a7ee00000 > > > > IMPORTANT: if you fix the bug, please add the following tag to the commit: > > Reported-by: syzbot+198362c76088d1515529@xxxxxxxxxxxxxxxxxxxxxxxxx > > > > ------------[ cut here ]------------ > > refcount_t: underflow; use-after-free. > > WARNING: CPU: 1 PID: 2940 at lib/refcount.c:28 refcount_warn_saturate+0x1dc/0x1f0 lib/refcount.c:28 > > Kernel panic - not syncing: panic_on_warn set ... > > CPU: 1 PID: 2940 Comm: kworker/1:12 Not tainted 5.6.0-rc2-next-20200221-syzkaller #0 > > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 > > Workqueue: events do_enable_set > > Call Trace: > > __dump_stack lib/dump_stack.c:77 [inline] > > dump_stack+0x197/0x210 lib/dump_stack.c:118 > > panic+0x2e3/0x75c kernel/panic.c:221 > > __warn.cold+0x2f/0x3e kernel/panic.c:582 > > report_bug+0x289/0x300 lib/bug.c:195 > > fixup_bug arch/x86/kernel/traps.c:175 [inline] > > fixup_bug arch/x86/kernel/traps.c:170 [inline] > > do_error_trap+0x11b/0x200 arch/x86/kernel/traps.c:267 > > do_invalid_op+0x37/0x50 arch/x86/kernel/traps.c:286 > > invalid_op+0x23/0x30 arch/x86/entry/entry_64.S:1027 > > RIP: 0010:refcount_warn_saturate+0x1dc/0x1f0 lib/refcount.c:28 > > Code: e9 d8 fe ff ff 48 89 df e8 81 81 10 fe e9 85 fe ff ff e8 07 54 d1 fd 48 c7 c7 00 c8 91 88 c6 05 6b f6 fc 06 01 e8 23 74 a1 fd <0f> 0b e9 ac fe ff ff 0f 1f 00 66 2e 0f 1f 84 00 00 00 00 00 55 48 > > RSP: 0018:ffffc9000952fbd8 EFLAGS: 00010286 > > RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000 > > RDX: 0000000000000000 RSI: ffffffff815ee766 RDI: fffff520012a5f6d > > RBP: ffffc9000952fbe8 R08: ffff88809e82e600 R09: ffffed1015d26661 > > R10: ffffed1015d26660 R11: ffff8880ae933307 R12: 0000000000000003 > > R13: ffff888095b3f018 R14: dead000000000122 R15: ffffc9000952fc98 > > refcount_sub_and_test include/linux/refcount.h:261 [inline] > > refcount_dec_and_test include/linux/refcount.h:281 [inline] > > kref_put include/linux/kref.h:64 [inline] > > l2cap_chan_put+0x1d9/0x240 net/bluetooth/l2cap_core.c:501 > > do_enable_set+0x54b/0x960 net/bluetooth/6lowpan.c:1075 > > process_one_work+0xa05/0x17a0 kernel/workqueue.c:2266 > > worker_thread+0x98/0xe40 kernel/workqueue.c:2412 > > kthread+0x361/0x430 kernel/kthread.c:255 > > ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352 > > Kernel Offset: disabled > > Rebooting in 86400 seconds.. > > > > > > --- > > 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. > > For information about bisection process see: https://goo.gl/tpsmEJ#bisection > > syzbot can test patches for this bug, for details see: > > https://goo.gl/tpsmEJ#testing-patches -- Luiz Augusto von Dentz
