Messages in this thread | | | From | Y Song <> | Date | Tue, 14 Aug 2018 08:59:04 -0700 | Subject | Re: WARNING: suspicious RCU usage in bpf_prog_array_copy_core |
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On Tue, Aug 14, 2018 at 2:40 AM, syzbot <syzbot+6e72317008eef84a216b@syzkaller.appspotmail.com> wrote: > Hello, > > syzbot found the following crash on: > > HEAD commit: 4110b42356f3 Add linux-next specific files for 20180810 > git tree: linux-next > console output: https://syzkaller.appspot.com/x/log.txt?x=109bac02400000 > kernel config: https://syzkaller.appspot.com/x/.config?x=1d80606e3795a4f5 > dashboard link: https://syzkaller.appspot.com/bug?extid=6e72317008eef84a216b > compiler: gcc (GCC) 8.0.1 20180413 (experimental) > syzkaller repro:https://syzkaller.appspot.com/x/repro.syz?x=157ef48a400000 > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=12e16cf8400000 > > IMPORTANT: if you fix the bug, please add the following tag to the commit: > Reported-by: syzbot+6e72317008eef84a216b@syzkaller.appspotmail.com > > random: sshd: uninitialized urandom read (32 bytes read) > random: sshd: uninitialized urandom read (32 bytes read) > random: sshd: uninitialized urandom read (32 bytes read) > > ============================= > WARNING: suspicious RCU usage > 4.18.0-rc8-next-20180810+ #36 Not tainted > ----------------------------- > kernel/bpf/core.c:1582 suspicious rcu_dereference_check() usage! > > other info that might help us debug this: > > > rcu_scheduler_active = 2, debug_locks = 1 > 2 locks held by syz-executor287/4449: > #0: 00000000d8131c0c (&ctx->mutex){+.+.}, at: > perf_event_ctx_lock_nested+0x375/0x600 kernel/events/core.c:1276 > #1: 000000006c916250 (bpf_event_mutex){+.+.}, at: > perf_event_query_prog_array+0x1c6/0x380 kernel/trace/bpf_trace.c:1062 > > stack backtrace: > CPU: 1 PID: 4449 Comm: syz-executor287 Not tainted 4.18.0-rc8-next-20180810+ > #36 > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS > Google 01/01/2011 > Call Trace: > __dump_stack lib/dump_stack.c:77 [inline] > dump_stack+0x1c9/0x2b4 lib/dump_stack.c:113 > lockdep_rcu_suspicious+0x14a/0x153 kernel/locking/lockdep.c:4562 > bpf_prog_array_copy_core+0x2d9/0x360 kernel/bpf/core.c:1582 > bpf_prog_array_copy_info+0x9a/0x110 kernel/bpf/core.c:1720 > perf_event_query_prog_array+0x22e/0x380 kernel/trace/bpf_trace.c:1063 > _perf_ioctl+0x986/0x1600 kernel/events/core.c:5079 > perf_ioctl+0x59/0x80 kernel/events/core.c:5110 > vfs_ioctl fs/ioctl.c:46 [inline] > file_ioctl fs/ioctl.c:501 [inline] > do_vfs_ioctl+0x1de/0x1720 fs/ioctl.c:685 > ksys_ioctl+0xa9/0xd0 fs/ioctl.c:702 > __do_sys_ioctl fs/ioctl.c:709 [inline] > __se_sys_ioctl fs/ioctl.c:707 [inline] > __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:707 > do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290 > entry_SYSCALL_64_after_hwframe+0x49/0xbe > RIP: 0033:0x440409 > Code: 18 89 d0 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 48 89 f8 48 89 f7 > 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff > 0f 83 fb 13 fc ff c3 66 2e 0f 1f 84 00 00 00 00 > RSP: 002b:00007fffc5fc1488 EFLAGS: 00000217 ORIG_RAX: 0000000000000010 > RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 0000000000440409 > RDX: 0000000020000180 RSI: 00000000c008240a RDI: 0000000000000003 > RBP: 00000000006ca018 R08: 00000000004002c8 R09: 00000000004002c8 > R10: 00000000004002c8 R11: 0000000000000217 R12: 0000000000401c90 > R13: 0000000000401d20 R14: 0000000000000000 >
I will take a look at this one. We have a mutex lock at kernel/trace/bpf_trace.c,
1062 mutex_lock(&bpf_event_mutex); 1063 ret = bpf_prog_array_copy_info(event->tp_event->prog_array, 1064 ids, 1065 ids_len, 1066 &prog_cnt); 1067 mutex_unlock(&bpf_event_mutex);
We may need a variant of rcu_dereference, e.g., rcu_dereference_protected.
> > --- > 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#bug-status-tracking for how to communicate with > syzbot. > syzbot can test patches for this bug, for details see: > https://goo.gl/tpsmEJ#testing-patches
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