Date:   Fri, 16 Mar 2018 22:26:39 +0800
From:   yongjian xu <yongjianchn@...il.com>
To:     Soheil Hassas Yeganeh <soheil.kdev@...il.com>
Cc:     davem@...emloft.net, netdev@...r.kernel.org, ycheng@...gle.com,
        ncardwell@...gle.com, nefelim4ag@...il.com,
        Soheil Hassas Yeganeh <soheil@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>
Subject: Re: [PATCH linux-stable-4.14] tcp: reset sk_send_head in tcp_write_queue_purge

Tested-by: Yongjian Xu <yongjianchn@...il.com>

2018-03-16 0:09 GMT+08:00 Soheil Hassas Yeganeh <soheil.kdev@...il.com>:
> From: Soheil Hassas Yeganeh <soheil@...gle.com>
>
> tcp_write_queue_purge clears all the SKBs in the write queue
> but does not reset the sk_send_head. As a result, we can have
> a NULL pointer dereference anywhere that we use tcp_send_head
> instead of the tcp_write_queue_tail.
>
> For example, after 27fid7a8ed38 (tcp: purge write queue upon RST),
> we can purge the write queue on RST. Prior to
> 75c119afe14f (tcp: implement rb-tree based retransmit queue),
> tcp_push will only check tcp_send_head and then accesses
> tcp_write_queue_tail to send the actual SKB. As a result, it will
> dereference a NULL pointer.
>
> This has been reported twice for 4.14 where we don't have
> 75c119afe14f:
>
> By Timofey Titovets:
>
> [  422.081094] BUG: unable to handle kernel NULL pointer dereference
> at 0000000000000038
> [  422.081254] IP: tcp_push+0x42/0x110
> [  422.081314] PGD 0 P4D 0
> [  422.081364] Oops: 0002 [#1] SMP PTI
>
> By Yongjian Xu:
>
> BUG: unable to handle kernel NULL pointer dereference at 0000000000000038
> IP: tcp_push+0x48/0x120
> PGD 80000007ff77b067 P4D 80000007ff77b067 PUD 7fd989067 PMD 0
> Oops: 0002 [#18] SMP PTI
> Modules linked in: tcp_diag inet_diag tcp_bbr sch_fq iTCO_wdt
> iTCO_vendor_support pcspkr ixgbe mdio i2c_i801 lpc_ich joydev input_leds shpchp
> e1000e igb dca ptp pps_core hwmon mei_me mei ipmi_si ipmi_msghandler sg ses
> scsi_transport_sas enclosure ext4 jbd2 mbcache sd_mod ahci libahci megaraid_sas
> wmi ast ttm dm_mirror dm_region_hash dm_log dm_mod dax
> CPU: 6 PID: 14156 Comm: [ET_NET 6] Tainted: G D 4.14.26-1.el6.x86_64 #1
> Hardware name: LENOVO ThinkServer RD440 /ThinkServer RD440, BIOS A0TS80A
> 09/22/2014
> task: ffff8807d78d8140 task.stack: ffffc9000e944000
> RIP: 0010:tcp_push+0x48/0x120
> RSP: 0018:ffffc9000e947a88 EFLAGS: 00010246
> RAX: 00000000000005b4 RBX: ffff880f7cce9c00 RCX: 0000000000000000
> RDX: 0000000000000000 RSI: 0000000000000040 RDI: ffff8807d00f5000
> RBP: ffffc9000e947aa8 R08: 0000000000001c84 R09: 0000000000000000
> R10: ffff8807d00f5158 R11: 0000000000000000 R12: ffff8807d00f5000
> R13: 0000000000000020 R14: 00000000000256d4 R15: 0000000000000000
> FS: 00007f5916de9700(0000) GS:ffff88107fd00000(0000) knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000000000000038 CR3: 00000007f8226004 CR4: 00000000001606e0
> Call Trace:
> tcp_sendmsg_locked+0x33d/0xe50
> tcp_sendmsg+0x37/0x60
> inet_sendmsg+0x39/0xc0
> sock_sendmsg+0x49/0x60
> sock_write_iter+0xb6/0x100
> do_iter_readv_writev+0xec/0x130
> ? rw_verify_area+0x49/0xb0
> do_iter_write+0x97/0xd0
> vfs_writev+0x7e/0xe0
> ? __wake_up_common_lock+0x80/0xa0
> ? __fget_light+0x2c/0x70
> ? __do_page_fault+0x1e7/0x530
> do_writev+0x60/0xf0
> ? inet_shutdown+0xac/0x110
> SyS_writev+0x10/0x20
> do_syscall_64+0x6f/0x140
> ? prepare_exit_to_usermode+0x8b/0xa0
> entry_SYSCALL_64_after_hwframe+0x3d/0xa2
> RIP: 0033:0x3135ce0c57
> RSP: 002b:00007f5916de4b00 EFLAGS: 00000293 ORIG_RAX: 0000000000000014
> RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 0000003135ce0c57
> RDX: 0000000000000002 RSI: 00007f5916de4b90 RDI: 000000000000606f
> RBP: 0000000000000000 R08: 0000000000000000 R09: 00007f5916de8c38
> R10: 0000000000000000 R11: 0000000000000293 R12: 00000000000464cc
> R13: 00007f5916de8c30 R14: 00007f58d8bef080 R15: 0000000000000002
> Code: 48 8b 97 60 01 00 00 4c 8d 97 58 01 00 00 41 b9 00 00 00 00 41 89 f3 4c 39
> d2 49 0f 44 d1 41 81 e3 00 80 00 00 0f 85 b0 00 00 00 <80> 4a 38 08 44 8b 8f 74
> 06 00 00 44 89 8f 7c 06 00 00 83 e6 01
> RIP: tcp_push+0x48/0x120 RSP: ffffc9000e947a88
> CR2: 0000000000000038
> ---[ end trace 8d545c2e93515549 ]---
>
> Fixes: a27fid7a8ed38 (tcp: purge write queue upon RST)
> Reported-by: Timofey Titovets <nefelim4ag@...il.com>
> Reported-by: Yongjian Xu <yongjianchn@...il.com>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Signed-off-by: Soheil Hassas Yeganeh <soheil@...gle.com>
> ---
>  include/net/tcp.h | 11 ++++++-----
>  1 file changed, 6 insertions(+), 5 deletions(-)
>
> diff --git a/include/net/tcp.h b/include/net/tcp.h
> index 0a13574134b8b..d323d4fa742ca 100644
> --- a/include/net/tcp.h
> +++ b/include/net/tcp.h
> @@ -1600,6 +1600,11 @@ enum tcp_chrono {
>  void tcp_chrono_start(struct sock *sk, const enum tcp_chrono type);
>  void tcp_chrono_stop(struct sock *sk, const enum tcp_chrono type);
>
> +static inline void tcp_init_send_head(struct sock *sk)
> +{
> +       sk->sk_send_head = NULL;
> +}
> +
>  /* write queue abstraction */
>  static inline void tcp_write_queue_purge(struct sock *sk)
>  {
> @@ -1610,6 +1615,7 @@ static inline void tcp_write_queue_purge(struct sock *sk)
>                 sk_wmem_free_skb(sk, skb);
>         sk_mem_reclaim(sk);
>         tcp_clear_all_retrans_hints(tcp_sk(sk));
> +       tcp_init_send_head(sk);
>  }
>
>  static inline struct sk_buff *tcp_write_queue_head(const struct sock *sk)
> @@ -1672,11 +1678,6 @@ static inline void tcp_check_send_head(struct sock *sk, struct sk_buff *skb_unli
>                 tcp_sk(sk)->highest_sack = NULL;
>  }
>
> -static inline void tcp_init_send_head(struct sock *sk)
> -{
> -       sk->sk_send_head = NULL;
> -}
> -
>  static inline void __tcp_add_write_queue_tail(struct sock *sk, struct sk_buff *skb)
>  {
>         __skb_queue_tail(&sk->sk_write_queue, skb);
> --
> 2.16.2.804.g6dcf76e118-goog
>

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