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Date:   Wed, 22 May 2019 14:57:33 -0700
From:   John Fastabend <john.fastabend@...il.com>
To:     Jakub Kicinski <jakub.kicinski@...ronome.com>,
        John Fastabend <john.fastabend@...il.com>
Cc:     ast@...nel.org, Eric Dumazet <edumazet@...gle.com>,
        netdev@...r.kernel.org,
        David Beckett <david.beckett@...ronome.com>,
        David Miller <davem@...emloft.net>
Subject: Re: [bpf PATCH v4 1/4] bpf: tls, implement unhash to avoid transition
 out of ESTABLISHED

Jakub Kicinski wrote:
> On Thu, 09 May 2019 21:57:49 -0700, John Fastabend wrote:

[...]

> 
> Looks like David Beckett managed to trigger another nasty on the
> release path :/
> 
>     BUG: kernel NULL pointer dereference, address: 0000000000000012
>     PGD 0 P4D 0
>     Oops: 0000 [#1] SMP PTI
>     CPU: 7 PID: 0 Comm: swapper/7 Not tainted
>     5.2.0-rc1-00139-g14629453a6d3 #21 RIP: 0010:tcp_peek_len+0x10/0x60
>     RSP: 0018:ffffc02e41c54b98 EFLAGS: 00010246
>     RAX: 0000000000000000 RBX: ffff9cf924c4e030 RCX: 0000000000000051
>     RDX: 0000000000000000 RSI: 000000000000000c RDI: ffff9cf97128f480
>     RBP: ffff9cf9365e0300 R08: ffff9cf94fe7d2c0 R09: 0000000000000000
>     R10: 000000000000036b R11: ffff9cf939735e00 R12: ffff9cf91ad9ae40
>     R13: ffff9cf924c4e000 R14: ffff9cf9a8fcbaae R15: 0000000000000020
>     FS: 0000000000000000(0000) GS:ffff9cf9af7c0000(0000)
>     knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0:
>     0000000080050033 CR2: 0000000000000012 CR3: 000000013920a003 CR4:
>     00000000003606e0 DR0: 0000000000000000 DR1: 0000000000000000 DR2:
>     0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7:
>     0000000000000400 Call Trace:
>      <IRQ>
>      strp_data_ready+0x48/0x90
>      tls_data_ready+0x22/0xd0 [tls]
>      tcp_rcv_established+0x569/0x620
>      tcp_v4_do_rcv+0x127/0x1e0
>      tcp_v4_rcv+0xad7/0xbf0
>      ip_protocol_deliver_rcu+0x2c/0x1c0
>      ip_local_deliver_finish+0x41/0x50
>      ip_local_deliver+0x6b/0xe0
>      ? ip_protocol_deliver_rcu+0x1c0/0x1c0
>      ip_rcv+0x52/0xd0
>      ? ip_rcv_finish_core.isra.20+0x380/0x380
>      __netif_receive_skb_one_core+0x7e/0x90
>      netif_receive_skb_internal+0x42/0xf0
>      napi_gro_receive+0xed/0x150
>      nfp_net_poll+0x7a2/0xd30 [nfp]
>      ? kmem_cache_free_bulk+0x286/0x310
>      net_rx_action+0x149/0x3b0
>      __do_softirq+0xe3/0x30a
>      ? handle_irq_event_percpu+0x6a/0x80
>      irq_exit+0xe8/0xf0
>      do_IRQ+0x85/0xd0
>      common_interrupt+0xf/0xf
>      </IRQ>
>     RIP: 0010:cpuidle_enter_state+0xbc/0x450
> 
> If I read this right strparser calls sock->ops->peek_len(sock), but the
> sock->sk is already NULL.  I'm guess this is because inet_release()
> does:
> 
> 		sock->sk = NULL;
> 		sk->sk_prot->close(sk, timeout);
> 
> And I don't really see a way for ktls to know that sock->sk is about to
> be cleared, and therefore no way to stop strparser.  Or for strparser
> to always do the check, given tcp_peek_len() will do another dereference
> of sock->sk :S
> 
> That's mostly a guess, it takes me half an hour of ktls connections
> running to repro.
> 
> Any advice would be appreciated..  Can we move the sock->sk assignment
> after close?..
> 
> diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
> index 5183a2daba64..aff93e7cdb31 100644
> --- a/net/ipv4/af_inet.c
> +++ b/net/ipv4/af_inet.c
> @@ -428,8 +428,8 @@ int inet_release(struct socket *sock)
>                 if (sock_flag(sk, SOCK_LINGER) &&
>                     !(current->flags & PF_EXITING))
>                         timeout = sk->sk_lingertime;
> -               sock->sk = NULL;
>                 sk->sk_prot->close(sk, timeout);
> +               sock->sk = NULL;
>         }
>         return 0;
>  }
> 
> I don't see IPv6 clearing this pointer, perhaps we don't have to?
> We tested it and it seems to works, but this is pre-git code, so
> it's hard to tell what the reason to clear was :)

How about making strp_peek_len tolerant of a null sock->sk?

diff --git a/net/strparser/strparser.c b/net/strparser/strparser.c
index e137698e8aef..79518f93d2d8 100644
--- a/net/strparser/strparser.c
+++ b/net/strparser/strparser.c
@@ -84,9 +84,10 @@ static void strp_parser_err(struct strparser *strp, int err,
 static inline int strp_peek_len(struct strparser *strp)
 {
        if (strp->sk) {
-               struct socket *sock = strp->sk->sk_socket;
+               struct socket *sock = READ_ONCE(strp->sk->sk_socket);
 
-               return sock->ops->peek_len(sock);
+               if (likely(sock))
+                       return sock->ops->peek_len(sock);
        }

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