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Date:   Wed, 19 Aug 2020 17:09:54 +0800
From:   Xin Long <lucien.xin@...il.com>
To:     syzbot <syzbot+47bbc6b678d317cccbe0@...kaller.appspotmail.com>
Cc:     davem <davem@...emloft.net>, Jon Maloy <jmaloy@...hat.com>,
        Jakub Kicinski <kuba@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        network dev <netdev@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        tipc-discussion@...ts.sourceforge.net,
        Ying Xue <ying.xue@...driver.com>
Subject: Re: WARNING: suspicious RCU usage in tipc_l2_send_msg

On Sat, Jun 27, 2020 at 1:25 AM syzbot
<syzbot+47bbc6b678d317cccbe0@...kaller.appspotmail.com> wrote:
>
> Hello,
>
> syzbot found the following crash on:
>
> HEAD commit:    b835a71e usbnet: smsc95xx: Fix use-after-free after removal
> git tree:       net
> console output: https://syzkaller.appspot.com/x/log.txt?x=1095a51d100000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=dcc6334acae363d4
> dashboard link: https://syzkaller.appspot.com/bug?extid=47bbc6b678d317cccbe0
> compiler:       gcc (GCC) 10.1.0-syz 20200507
>
> Unfortunately, I don't have any reproducer for this crash yet.
>
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+47bbc6b678d317cccbe0@...kaller.appspotmail.com
>
> =============================
> WARNING: suspicious RCU usage
> 5.8.0-rc1-syzkaller #0 Not tainted
> -----------------------------
> net/tipc/bearer.c:466 suspicious rcu_dereference_check() usage!
>
> other info that might help us debug this:
>
>
> rcu_scheduler_active = 2, debug_locks = 1
> 2 locks held by kworker/0:16/19143:
>  #0: ffff8880a6901d38 ((wq_completion)cryptd){+.+.}-{0:0}, at: arch_atomic64_set arch/x86/include/asm/atomic64_64.h:34 [inline]
>  #0: ffff8880a6901d38 ((wq_completion)cryptd){+.+.}-{0:0}, at: atomic64_set include/asm-generic/atomic-instrumented.h:856 [inline]
>  #0: ffff8880a6901d38 ((wq_completion)cryptd){+.+.}-{0:0}, at: atomic_long_set include/asm-generic/atomic-long.h:41 [inline]
>  #0: ffff8880a6901d38 ((wq_completion)cryptd){+.+.}-{0:0}, at: set_work_data kernel/workqueue.c:616 [inline]
>  #0: ffff8880a6901d38 ((wq_completion)cryptd){+.+.}-{0:0}, at: set_work_pool_and_clear_pending kernel/workqueue.c:643 [inline]
>  #0: ffff8880a6901d38 ((wq_completion)cryptd){+.+.}-{0:0}, at: process_one_work+0x82b/0x1670 kernel/workqueue.c:2240
>  #1: ffffc90006f9fda8 ((work_completion)(&cpu_queue->work)){+.+.}-{0:0}, at: process_one_work+0x85f/0x1670 kernel/workqueue.c:2244
>
> stack backtrace:
> CPU: 0 PID: 19143 Comm: kworker/0:16 Not tainted 5.8.0-rc1-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Workqueue: cryptd cryptd_queue_worker
> Call Trace:
>  __dump_stack lib/dump_stack.c:77 [inline]
>  dump_stack+0x18f/0x20d lib/dump_stack.c:118
>  tipc_l2_send_msg+0x354/0x420 net/tipc/bearer.c:466
>  tipc_aead_encrypt_done+0x204/0x3a0 net/tipc/crypto.c:761
>  cryptd_aead_crypt+0xe8/0x1d0 crypto/cryptd.c:739
>  cryptd_queue_worker+0x118/0x1b0 crypto/cryptd.c:181
>  process_one_work+0x94c/0x1670 kernel/workqueue.c:2269
>  worker_thread+0x64c/0x1120 kernel/workqueue.c:2415
>  kthread+0x3b5/0x4a0 kernel/kthread.c:291
>  ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:293
>
Like in bearer.c, rcu_read_lock() is needed before calling
b->media->send_msg() in tipc_aead_encrypt_done():

@@ -757,10 +757,12 @@ static void tipc_aead_encrypt_done(struct
crypto_async_request *base, int err)
        switch (err) {
        case 0:
                this_cpu_inc(tx->stats->stat[STAT_ASYNC_OK]);
+               rcu_read_lock();
                if (likely(test_bit(0, &b->up)))
                        b->media->send_msg(net, skb, b, &tx_ctx->dst);
                else
                        kfree_skb(skb);
+               rcu_read_unlock();
                break;
>
> ---
> This bug is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@...glegroups.com.
>
> syzbot will keep track of this bug report. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

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