Re: suspicious RCU usage at net/ipv6/ip6_fib.c:LINE

On Thu, Feb 1, 2018 at 2:56 PM, Eric Biggers [off-list ref] wrote:

+weiwan@google.com

On Tue, Jan 02, 2018 at 03:58:02PM -0800, syzbot wrote:

quoted

Hello,

syzkaller hit the following crash on
6bb8824732f69de0f233ae6b1a8158e149627b38
git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next.git/master
compiler: gcc (GCC) 7.1.1 20170620
.config is attached
Raw console output is attached.
C reproducer is attached
syzkaller reproducer is attached. See https://goo.gl/kgGztJ
for information about syzkaller reproducers


IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+bca7109dba5d86cb0209@syzkaller.appspotmail.com
It will help syzbot understand when the bug is fixed. See footer for
details.
If you forward the report, please keep this part and the footer.


=============================
WARNING: suspicious RCU usage
4.15.0-rc5+ #171 Not tainted
-----------------------------
net/ipv6/ip6_fib.c:1702 suspicious rcu_dereference_protected() usage!

other info that might help us debug this:


rcu_scheduler_active = 2, debug_locks = 1
4 locks held by swapper/0/0:
 #0:  ((&net->ipv6.ip6_fib_timer)){+.-.}, at: [<00000000d43f631b>]
lockdep_copy_map include/linux/lockdep.h:178 [inline]
 #0:  ((&net->ipv6.ip6_fib_timer)){+.-.}, at: [<00000000d43f631b>]
call_timer_fn+0x1c6/0x820 kernel/time/timer.c:1310
 #1:  (&(&net->ipv6.fib6_gc_lock)->rlock){+.-.}, at: [<000000002ff9d65c>]
spin_lock_bh include/linux/spinlock.h:315 [inline]
 #1:  (&(&net->ipv6.fib6_gc_lock)->rlock){+.-.}, at: [<000000002ff9d65c>]
fib6_run_gc+0x9d/0x3c0 net/ipv6/ip6_fib.c:2007
 #2:  (rcu_read_lock){....}, at: [<0000000091db762d>]
__fib6_clean_all+0x0/0x3a0 net/ipv6/ip6_fib.c:1560
 #3:  (&(&tb->tb6_lock)->rlock){+.-.}, at: [<000000009e503581>] spin_lock_bh
include/linux/spinlock.h:315 [inline]
 #3:  (&(&tb->tb6_lock)->rlock){+.-.}, at: [<000000009e503581>]
__fib6_clean_all+0x1d0/0x3a0 net/ipv6/ip6_fib.c:1948

stack backtrace:
CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.15.0-rc5+ #171
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Call Trace:
 <IRQ>
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0x194/0x257 lib/dump_stack.c:53
 lockdep_rcu_suspicious+0x123/0x170 kernel/locking/lockdep.c:4585
 fib6_del+0xcaa/0x11b0 net/ipv6/ip6_fib.c:1701
 fib6_clean_node+0x3aa/0x4f0 net/ipv6/ip6_fib.c:1892
 fib6_walk_continue+0x46c/0x8a0 net/ipv6/ip6_fib.c:1815
 fib6_walk+0x91/0xf0 net/ipv6/ip6_fib.c:1863
 fib6_clean_tree+0x1e6/0x340 net/ipv6/ip6_fib.c:1933
 __fib6_clean_all+0x1f4/0x3a0 net/ipv6/ip6_fib.c:1949
 fib6_clean_all net/ipv6/ip6_fib.c:1960 [inline]
 fib6_run_gc+0x16b/0x3c0 net/ipv6/ip6_fib.c:2016
 fib6_gc_timer_cb+0x20/0x30 net/ipv6/ip6_fib.c:2033
 call_timer_fn+0x228/0x820 kernel/time/timer.c:1320
 expire_timers kernel/time/timer.c:1357 [inline]
 __run_timers+0x7ee/0xb70 kernel/time/timer.c:1660
 run_timer_softirq+0x4c/0xb0 kernel/time/timer.c:1686
 __do_softirq+0x2d7/0xb85 kernel/softirq.c:285
 invoke_softirq kernel/softirq.c:365 [inline]
 irq_exit+0x1cc/0x200 kernel/softirq.c:405
 exiting_irq arch/x86/include/asm/apic.h:540 [inline]
 smp_apic_timer_interrupt+0x16b/0x700 arch/x86/kernel/apic/apic.c:1052
 apic_timer_interrupt+0xa9/0xb0 arch/x86/entry/entry_64.S:904
 </IRQ>
RIP: 0010:native_safe_halt+0x6/0x10 arch/x86/include/asm/irqflags.h:54
RSP: 0018:ffffffff86407c38 EFLAGS: 00000282 ORIG_RAX: ffffffffffffff11
RAX: dffffc0000000000 RBX: 1ffffffff0c80f8a RCX: 0000000000000000
RDX: 1ffffffff0c99048 RSI: 0000000000000001 RDI: ffffffff864c8240
RBP: ffffffff86407c38 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: ffffffff86407cf0 R14: ffffffff86c329a0 R15: 0000000000000000
 arch_safe_halt arch/x86/include/asm/paravirt.h:93 [inline]
 default_idle+0xbf/0x460 arch/x86/kernel/process.c:355
 arch_cpu_idle+0xa/0x10 arch/x86/kernel/process.c:346
 default_idle_call+0x36/0x90 kernel/sched/idle.c:98
 cpuidle_idle_call kernel/sched/idle.c:156 [inline]
 do_idle+0x24a/0x3b0 kernel/sched/idle.c:246
 cpu_startup_entry+0x104/0x120 kernel/sched/idle.c:351
 rest_init+0xed/0xf0 init/main.c:435
 start_kernel+0x7f1/0x819 init/main.c:713
 x86_64_start_reservations+0x2a/0x2c arch/x86/kernel/head64.c:378
 x86_64_start_kernel+0x77/0x7a arch/x86/kernel/head64.c:359
 secondary_startup_64+0xa5/0xb0 arch/x86/kernel/head_64.S:237

Wei, was this meant to have been fixed by commit 4512c43eac7e00 ("ipv6: remove
null_entry before adding default route")?  This crash actually still occurred on

Yes. I would think so.

net-next as recently as 43df215d99e604 (Jan 25) which included your fix.  I will
go ahead and mark this bug fixed, but syzbot will send a new report if it hits
it again.

OK. Got it.

#syz fix: ipv6: remove null_entry before adding default route

- Eric