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Date:   Fri, 27 Jan 2017 15:35:24 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     David Miller <davem@...emloft.net>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        Eric Dumazet <edumazet@...gle.com>,
        James Morris <jmorris@...ei.org>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Patrick McHardy <kaber@...sh.net>,
        netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        netfilter-devel@...r.kernel.org,
        syzkaller <syzkaller@...glegroups.com>
Subject: Re: net: suspicious RCU usage in nf_hook

On Fri, 2017-01-27 at 22:15 +0100, Dmitry Vyukov wrote:
> Hello,
> 
> I've got the following report while running syzkaller fuzzer on
> fd694aaa46c7ed811b72eb47d5eb11ce7ab3f7f1:
> 
> [ INFO: suspicious RCU usage. ]
> 4.10.0-rc5+ #192 Not tainted
> -------------------------------
> ./include/linux/rcupdate.h:561 Illegal context switch in RCU read-side
> critical section!
> 
> other info that might help us debug this:
> 
> rcu_scheduler_active = 2, debug_locks = 0
> 2 locks held by syz-executor14/23111:
>  #0:  (sk_lock-AF_INET6){+.+.+.}, at: [<ffffffff83a35c35>] lock_sock
> include/net/sock.h:1454 [inline]
>  #0:  (sk_lock-AF_INET6){+.+.+.}, at: [<ffffffff83a35c35>]
> rawv6_sendmsg+0x1e65/0x3ec0 net/ipv6/raw.c:919
>  #1:  (rcu_read_lock){......}, at: [<ffffffff83ae2678>] nf_hook
> include/linux/netfilter.h:201 [inline]
>  #1:  (rcu_read_lock){......}, at: [<ffffffff83ae2678>]
> __ip6_local_out+0x258/0x840 net/ipv6/output_core.c:160
> 
> stack backtrace:
> CPU: 2 PID: 23111 Comm: syz-executor14 Not tainted 4.10.0-rc5+ #192
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
> Call Trace:
>  __dump_stack lib/dump_stack.c:15 [inline]
>  dump_stack+0x2ee/0x3ef lib/dump_stack.c:51
>  lockdep_rcu_suspicious+0x139/0x180 kernel/locking/lockdep.c:4452
>  rcu_preempt_sleep_check include/linux/rcupdate.h:560 [inline]
>  ___might_sleep+0x560/0x650 kernel/sched/core.c:7748
>  __might_sleep+0x95/0x1a0 kernel/sched/core.c:7739
>  mutex_lock_nested+0x24f/0x1730 kernel/locking/mutex.c:752
>  atomic_dec_and_mutex_lock+0x119/0x160 kernel/locking/mutex.c:1060
>  __static_key_slow_dec+0x7a/0x1e0 kernel/jump_label.c:149
>  static_key_slow_dec+0x51/0x90 kernel/jump_label.c:174
>  net_disable_timestamp+0x3b/0x50 net/core/dev.c:1728
>  sock_disable_timestamp+0x98/0xc0 net/core/sock.c:403
>  __sk_destruct+0x27d/0x6b0 net/core/sock.c:1441
>  sk_destruct+0x47/0x80 net/core/sock.c:1460
>  __sk_free+0x57/0x230 net/core/sock.c:1468
>  sock_wfree+0xae/0x120 net/core/sock.c:1645
>  skb_release_head_state+0xfc/0x200 net/core/skbuff.c:655
>  skb_release_all+0x15/0x60 net/core/skbuff.c:668
>  __kfree_skb+0x15/0x20 net/core/skbuff.c:684
>  kfree_skb+0x16e/0x4c0 net/core/skbuff.c:705
>  inet_frag_destroy+0x121/0x290 net/ipv4/inet_fragment.c:304
>  inet_frag_put include/net/inet_frag.h:133 [inline]
>  nf_ct_frag6_gather+0x1106/0x3840 net/ipv6/netfilter/nf_conntrack_reasm.c:617
>  ipv6_defrag+0x1be/0x2b0 net/ipv6/netfilter/nf_defrag_ipv6_hooks.c:68
>  nf_hook_entry_hookfn include/linux/netfilter.h:102 [inline]
>  nf_hook_slow+0xc3/0x290 net/netfilter/core.c:310
>  nf_hook include/linux/netfilter.h:212 [inline]
>  __ip6_local_out+0x489/0x840 net/ipv6/output_core.c:160
>  ip6_local_out+0x2d/0x170 net/ipv6/output_core.c:170
>  ip6_send_skb+0xa1/0x340 net/ipv6/ip6_output.c:1722
>  ip6_push_pending_frames+0xb3/0xe0 net/ipv6/ip6_output.c:1742
>  rawv6_push_pending_frames net/ipv6/raw.c:613 [inline]
>  rawv6_sendmsg+0x2d1a/0x3ec0 net/ipv6/raw.c:927
>  inet_sendmsg+0x164/0x5b0 net/ipv4/af_inet.c:744
>  sock_sendmsg_nosec net/socket.c:635 [inline]
>  sock_sendmsg+0xca/0x110 net/socket.c:645
>  sock_write_iter+0x326/0x600 net/socket.c:848
>  do_iter_readv_writev+0x2e3/0x5b0 fs/read_write.c:695
>  do_readv_writev+0x42c/0x9b0 fs/read_write.c:872
>  vfs_writev+0x87/0xc0 fs/read_write.c:911
>  do_writev+0x110/0x2c0 fs/read_write.c:944
>  SYSC_writev fs/read_write.c:1017 [inline]
>  SyS_writev+0x27/0x30 fs/read_write.c:1014
>  entry_SYSCALL_64_fastpath+0x1f/0xc2
> RIP: 0033:0x445559
> RSP: 002b:00007f6f46fceb58 EFLAGS: 00000292 ORIG_RAX: 0000000000000014
> RAX: ffffffffffffffda RBX: 0000000000000005 RCX: 0000000000445559
> RDX: 0000000000000001 RSI: 0000000020f1eff0 RDI: 0000000000000005
> RBP: 00000000006e19c0 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000292 R12: 0000000000700000
> R13: 0000000020f59000 R14: 0000000000000015 R15: 0000000000020400
> BUG: sleeping function called from invalid context at kernel/locking/mutex.c:752
> in_atomic(): 1, irqs_disabled(): 0, pid: 23111, name: syz-executor14
> INFO: lockdep is turned off.
> CPU: 2 PID: 23111 Comm: syz-executor14 Not tainted 4.10.0-rc5+ #192
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
> Call Trace:
>  __dump_stack lib/dump_stack.c:15 [inline]
>  dump_stack+0x2ee/0x3ef lib/dump_stack.c:51
>  ___might_sleep+0x47e/0x650 kernel/sched/core.c:7780
>  __might_sleep+0x95/0x1a0 kernel/sched/core.c:7739
>  mutex_lock_nested+0x24f/0x1730 kernel/locking/mutex.c:752
>  atomic_dec_and_mutex_lock+0x119/0x160 kernel/locking/mutex.c:1060
>  __static_key_slow_dec+0x7a/0x1e0 kernel/jump_label.c:149
>  static_key_slow_dec+0x51/0x90 kernel/jump_label.c:174
>  net_disable_timestamp+0x3b/0x50 net/core/dev.c:1728
>  sock_disable_timestamp+0x98/0xc0 net/core/sock.c:403
>  __sk_destruct+0x27d/0x6b0 net/core/sock.c:1441
>  sk_destruct+0x47/0x80 net/core/sock.c:1460
>  __sk_free+0x57/0x230 net/core/sock.c:1468
>  sock_wfree+0xae/0x120 net/core/sock.c:1645
>  skb_release_head_state+0xfc/0x200 net/core/skbuff.c:655
>  skb_release_all+0x15/0x60 net/core/skbuff.c:668
>  __kfree_skb+0x15/0x20 net/core/skbuff.c:684
>  kfree_skb+0x16e/0x4c0 net/core/skbuff.c:705
>  inet_frag_destroy+0x121/0x290 net/ipv4/inet_fragment.c:304
>  inet_frag_put include/net/inet_frag.h:133 [inline]
>  nf_ct_frag6_gather+0x1106/0x3840 net/ipv6/netfilter/nf_conntrack_reasm.c:617
>  ipv6_defrag+0x1be/0x2b0 net/ipv6/netfilter/nf_defrag_ipv6_hooks.c:68
>  nf_hook_entry_hookfn include/linux/netfilter.h:102 [inline]
>  nf_hook_slow+0xc3/0x290 net/netfilter/core.c:310
>  nf_hook include/linux/netfilter.h:212 [inline]
>  __ip6_local_out+0x489/0x840 net/ipv6/output_core.c:160
>  ip6_local_out+0x2d/0x170 net/ipv6/output_core.c:170
>  ip6_send_skb+0xa1/0x340 net/ipv6/ip6_output.c:1722
>  ip6_push_pending_frames+0xb3/0xe0 net/ipv6/ip6_output.c:1742
>  rawv6_push_pending_frames net/ipv6/raw.c:613 [inline]
>  rawv6_sendmsg+0x2d1a/0x3ec0 net/ipv6/raw.c:927
>  inet_sendmsg+0x164/0x5b0 net/ipv4/af_inet.c:744
>  sock_sendmsg_nosec net/socket.c:635 [inline]
>  sock_sendmsg+0xca/0x110 net/socket.c:645
>  sock_write_iter+0x326/0x600 net/socket.c:848
>  do_iter_readv_writev+0x2e3/0x5b0 fs/read_write.c:695
>  do_readv_writev+0x42c/0x9b0 fs/read_write.c:872
>  vfs_writev+0x87/0xc0 fs/read_write.c:911
>  do_writev+0x110/0x2c0 fs/read_write.c:944
>  SYSC_writev fs/read_write.c:1017 [inline]
>  SyS_writev+0x27/0x30 fs/read_write.c:1014
>  entry_SYSCALL_64_fastpath+0x1f/0xc2

Oh well, I forgot to submit the official patch I think, Jan 9th.

https://groups.google.com/forum/#!topic/syzkaller/BhyN5OFd7sQ

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