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Date:   Sat, 23 Nov 2019 09:56:50 -0300
From:   Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
To:     Xin Long <lucien.xin@...il.com>
Cc:     network dev <netdev@...r.kernel.org>, linux-sctp@...r.kernel.org,
        davem@...emloft.net, Neil Horman <nhorman@...driver.com>
Subject: Re: [PATCH net] sctp: cache netns in sctp_ep_common

On Sat, Nov 23, 2019 at 11:56:49AM +0800, Xin Long wrote:
> This patch is to fix a data-race reported by syzbot:
> 
>   BUG: KCSAN: data-race in sctp_assoc_migrate / sctp_hash_obj
> 
>   write to 0xffff8880b67c0020 of 8 bytes by task 18908 on cpu 1:
>     sctp_assoc_migrate+0x1a6/0x290 net/sctp/associola.c:1091
>     sctp_sock_migrate+0x8aa/0x9b0 net/sctp/socket.c:9465
>     sctp_accept+0x3c8/0x470 net/sctp/socket.c:4916
>     inet_accept+0x7f/0x360 net/ipv4/af_inet.c:734
>     __sys_accept4+0x224/0x430 net/socket.c:1754
>     __do_sys_accept net/socket.c:1795 [inline]
>     __se_sys_accept net/socket.c:1792 [inline]
>     __x64_sys_accept+0x4e/0x60 net/socket.c:1792
>     do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290
>     entry_SYSCALL_64_after_hwframe+0x44/0xa9
> 
>   read to 0xffff8880b67c0020 of 8 bytes by task 12003 on cpu 0:
>     sctp_hash_obj+0x4f/0x2d0 net/sctp/input.c:894
>     rht_key_get_hash include/linux/rhashtable.h:133 [inline]
>     rht_key_hashfn include/linux/rhashtable.h:159 [inline]
>     rht_head_hashfn include/linux/rhashtable.h:174 [inline]
>     head_hashfn lib/rhashtable.c:41 [inline]
>     rhashtable_rehash_one lib/rhashtable.c:245 [inline]
>     rhashtable_rehash_chain lib/rhashtable.c:276 [inline]
>     rhashtable_rehash_table lib/rhashtable.c:316 [inline]
>     rht_deferred_worker+0x468/0xab0 lib/rhashtable.c:420
>     process_one_work+0x3d4/0x890 kernel/workqueue.c:2269
>     worker_thread+0xa0/0x800 kernel/workqueue.c:2415
>     kthread+0x1d4/0x200 drivers/block/aoe/aoecmd.c:1253
>     ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352
> 
> It was caused by rhashtable access asoc->base.sk when sctp_assoc_migrate
> is changing its value. However, what rhashtable wants is netns from asoc
> base.sk, and for an asoc, its netns won't change once set. So we can
> simply fix it by caching netns since created.
> 
> Fixes: d6c0256a60e6 ("sctp: add the rhashtable apis for sctp global transport hashtable")
> Reported-by: syzbot+e3b35fe7918ff0ee474e@...kaller.appspotmail.com
> Signed-off-by: Xin Long <lucien.xin@...il.com>

Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@...il.com>

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