Re: WARNING: suspicious RCU usage in rt6_check_expired

[Eric Dumazet]

On 04/23/2018 01:24 AM, syzbot wrote:
> Hello,
> 
> syzbot hit the following crash on net-next commit
> 0638eb573cde5888c0886c7f35da604e5db209a6 (Sat Apr 21 20:06:14 2018 +0000)
> Merge branch 'ipv6-Another-followup-to-the-fib6_info-change'
> syzbot dashboard link: https://syzkaller.appspot.com/bug?extid=2422c9e35796659d2273
> 
> So far this crash happened 3 times on net-next.
> Unfortunately, I don't have any reproducer for this crash yet.
> Raw console output: https://syzkaller.appspot.com/x/log.txt?id=6081013801287680
> Kernel config: https://syzkaller.appspot.com/x/.config?id=-8412024688694752032
> compiler: gcc (GCC) 8.0.1 20180413 (experimental)
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+2422c9e35796659d2273@xxxxxxxxxxxxxxxxxxxxxxxxx
> 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.
> 
> netlink: 'syz-executor4': attribute type 6 has an invalid length.
> netlink: 'syz-executor4': attribute type 1 has an invalid length.
> netlink: 'syz-executor4': attribute type 6 has an invalid length.
> 
> =============================
> WARNING: suspicious RCU usage
> 4.16.0+ #11 Not tainted
> -----------------------------
> net/ipv6/route.c:410 suspicious rcu_dereference_check() usage!
> 
> other info that might help us debug this:
> 
> 
> rcu_scheduler_active = 2, debug_locks = 1
> 1 lock held by syz-executor7/25958:
> Â#0: 00000000d1963139 (sk_lock-AF_INET6){+.+.}, at: lock_sock include/net/sock.h:1469 [inline]
> Â#0: 00000000d1963139 (sk_lock-AF_INET6){+.+.}, at: sock_setsockopt+0x19c/0x1fe0 net/core/sock.c:717
> 
> stack backtrace:
> CPU: 1 PID: 25958 Comm: syz-executor7 Not tainted 4.16.0+ #11
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Call Trace:
> Â__dump_stack lib/dump_stack.c:77 [inline]
> Âdump_stack+0x1b9/0x294 lib/dump_stack.c:113
> Âlockdep_rcu_suspicious+0x14a/0x153 kernel/locking/lockdep.c:4592
> Ârt6_check_expired+0x38b/0x3e0 net/ipv6/route.c:410
> Âip6_negative_advice+0x67/0xc0 net/ipv6/route.c:2204
> Âdst_negative_advice include/net/sock.h:1786 [inline]
> Âsock_setsockopt+0x138f/0x1fe0 net/core/sock.c:1051
> Â__sys_setsockopt+0x2df/0x390 net/socket.c:1899
> ÂSYSC_setsockopt net/socket.c:1914 [inline]
> ÂSyS_setsockopt+0x34/0x50 net/socket.c:1911
> Âdo_syscall_64+0x29e/0x9d0 arch/x86/entry/common.c:287
> Âentry_SYSCALL_64_after_hwframe+0x42/0xb7
> RIP: 0033:0x455389
> RSP: 002b:00007f7556e30c68 EFLAGS: 00000246 ORIG_RAX: 0000000000000036
> RAX: ffffffffffffffda RBX: 00007f7556e316d4 RCX: 0000000000455389
> RDX: 0000000000000035 RSI: 0000000000000001 RDI: 0000000000000013
> RBP: 000000000072bf58 R08: 0000000000000004 R09: 0000000000000000
> R10: 0000000020000000 R11: 0000000000000246 R12: 00000000ffffffff
> R13: 00000000000005ff R14: 00000000006fc088 R15: 0000000000000001
> netlink: 'syz-executor4': attribute type 4 has an invalid length.
> netlink: 'syz-executor4': attribute type 4 has an invalid length.
> IPVS: set_ctl: invalid protocol: 59 127.0.0.1:20000 lc
> IPVS: set_ctl: invalid protocol: 127 224.0.0.1:20000 rr
> IPVS: sync thread started: state = BACKUP, mcast_ifn = ip6tnl0, syncid = 4, id = 0
> IPVS: set_ctl: invalid protocol: 127 224.0.0.1:20000 rr
> netlink: 72 bytes leftover after parsing attributes in process `syz-executor2'.
> netlink: 72 bytes leftover after parsing attributes in process `syz-executor2'.
> dccp_xmit_packet: Payload too large (65423) for featneg.
> IPVS: set_ctl: invalid protocol: 29 1.0.0.0:2 wlc
> IPVS: set_ctl: invalid protocol: 29 1.0.0.0:2 wlc
> netlink: 32 bytes leftover after parsing attributes in process `syz-executor7'.
> netlink: 12 bytes leftover after parsing attributes in process `syz-executor1'.
> netlink: 12 bytes leftover after parsing attributes in process `syz-executor1'.
> netlink: 'syz-executor1': attribute type 29 has an invalid length.
> netlink: 8 bytes leftover after parsing attributes in process `syz-executor1'.
> IPVS: set_ctl: invalid protocol: 108 224.0.0.1:20004 lblc
> netlink: 'syz-executor1': attribute type 29 has an invalid length.
> netlink: 8 bytes leftover after parsing attributes in process `syz-executor1'.
> IPVS: set_ctl: invalid protocol: 108 224.0.0.1:20004 lblc
> 
> 
> ---
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Added in commit a68886a691804d3f6d479ebf6825480fbafb6a00
("net/ipv6: Make from in rt6_info rcu protected")