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Date:   Wed, 24 Apr 2019 09:27:10 +0100
From:   David Howells <dhowells@...hat.com>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     dhowells@...hat.com, "David S . Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <eric.dumazet@...il.com>,
        syzbot <syzkaller@...glegroups.com>
Subject: Re: [PATCH v3 net] rxrpc: fix race condition in rxrpc_input_packet()

Eric Dumazet <edumazet@...gle.com> wrote:

> After commit 5271953cad31 ("rxrpc: Use the UDP encap_rcv hook"),
> rxrpc_input_packet() is directly called from lockless UDP receive
> path, under rcu_read_lock() protection.
> 
> It must therefore use RCU rules :
> 
> - udp_sk->sk_user_data can be cleared at any point in this function.
>   rcu_dereference_sk_user_data() is what we need here.
> 
> - Also, since sk_user_data might have been set in rxrpc_open_socket()
>   we must observe a proper RCU grace period before kfree(local) in
>   rxrpc_lookup_local()
> 
> syzbot reported :
> 
> kasan: CONFIG_KASAN_INLINE enabled
> kasan: GPF could be caused by NULL-ptr deref or user memory access
> general protection fault: 0000 [#1] PREEMPT SMP KASAN
> CPU: 0 PID: 19236 Comm: syz-executor703 Not tainted 5.1.0-rc6 #79
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> RIP: 0010:__lock_acquire+0xbef/0x3fb0 kernel/locking/lockdep.c:3573
> Code: 00 0f 85 a5 1f 00 00 48 81 c4 10 01 00 00 5b 41 5c 41 5d 41 5e 41 5f 5d c3 48 b8 00 00 00 00 00 fc ff df 4c 89 ea 48 c1 ea 03 <80> 3c 02 00 0f 85 4a 21 00 00 49 81 7d 00 20 54 9c 89 0f 84 cf f4
> RSP: 0018:ffff88809d7aef58 EFLAGS: 00010002
> RAX: dffffc0000000000 RBX: 0000000000000000 RCX: 0000000000000000
> RDX: 0000000000000026 RSI: 0000000000000000 RDI: 0000000000000001
> RBP: ffff88809d7af090 R08: 0000000000000001 R09: 0000000000000001
> R10: ffffed1015d05bc7 R11: ffff888089428600 R12: 0000000000000000
> R13: 0000000000000130 R14: 0000000000000001 R15: 0000000000000001
> FS:  00007f059044d700(0000) GS:ffff8880ae800000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00000000004b6040 CR3: 00000000955ca000 CR4: 00000000001406f0
> Call Trace:
>  lock_acquire+0x16f/0x3f0 kernel/locking/lockdep.c:4211
>  __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
>  _raw_spin_lock_irqsave+0x95/0xcd kernel/locking/spinlock.c:152
>  skb_queue_tail+0x26/0x150 net/core/skbuff.c:2972
>  rxrpc_reject_packet net/rxrpc/input.c:1126 [inline]
>  rxrpc_input_packet+0x4a0/0x5536 net/rxrpc/input.c:1414
>  udp_queue_rcv_one_skb+0xaf2/0x1780 net/ipv4/udp.c:2011
>  udp_queue_rcv_skb+0x128/0x730 net/ipv4/udp.c:2085
>  udp_unicast_rcv_skb.isra.0+0xb9/0x360 net/ipv4/udp.c:2245
>  __udp4_lib_rcv+0x701/0x2ca0 net/ipv4/udp.c:2301
>  udp_rcv+0x22/0x30 net/ipv4/udp.c:2482
>  ip_protocol_deliver_rcu+0x60/0x8f0 net/ipv4/ip_input.c:208
>  ip_local_deliver_finish+0x23b/0x390 net/ipv4/ip_input.c:234
>  NF_HOOK include/linux/netfilter.h:289 [inline]
>  NF_HOOK include/linux/netfilter.h:283 [inline]
>  ip_local_deliver+0x1e9/0x520 net/ipv4/ip_input.c:255
>  dst_input include/net/dst.h:450 [inline]
>  ip_rcv_finish+0x1e1/0x300 net/ipv4/ip_input.c:413
>  NF_HOOK include/linux/netfilter.h:289 [inline]
>  NF_HOOK include/linux/netfilter.h:283 [inline]
>  ip_rcv+0xe8/0x3f0 net/ipv4/ip_input.c:523
>  __netif_receive_skb_one_core+0x115/0x1a0 net/core/dev.c:4987
>  __netif_receive_skb+0x2c/0x1c0 net/core/dev.c:5099
>  netif_receive_skb_internal+0x117/0x660 net/core/dev.c:5202
>  napi_frags_finish net/core/dev.c:5769 [inline]
>  napi_gro_frags+0xade/0xd10 net/core/dev.c:5843
>  tun_get_user+0x2f24/0x3fb0 drivers/net/tun.c:1981
>  tun_chr_write_iter+0xbd/0x156 drivers/net/tun.c:2027
>  call_write_iter include/linux/fs.h:1866 [inline]
>  do_iter_readv_writev+0x5e1/0x8e0 fs/read_write.c:681
>  do_iter_write fs/read_write.c:957 [inline]
>  do_iter_write+0x184/0x610 fs/read_write.c:938
>  vfs_writev+0x1b3/0x2f0 fs/read_write.c:1002
>  do_writev+0x15e/0x370 fs/read_write.c:1037
>  __do_sys_writev fs/read_write.c:1110 [inline]
>  __se_sys_writev fs/read_write.c:1107 [inline]
>  __x64_sys_writev+0x75/0xb0 fs/read_write.c:1107
>  do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290
>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> 
> Fixes: 5271953cad31 ("rxrpc: Use the UDP encap_rcv hook")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Reported-by: syzbot <syzkaller@...glegroups.com>

Acked-by: David Howells <dhowells@...hat.com>

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