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Subject: Re: WARNING in isotp_tx_timer_handler
To:     Hillf Danton <hdanton@sina.com>,
        syzbot <syzbot+78bab6958a614b0c80b9@syzkaller.appspotmail.com>
Cc:     linux-can@vger.kernel.org, linux-kernel@vger.kernel.org,
        mkl@pengutronix.de, netdev@vger.kernel.org,
        syzkaller-bugs@googlegroups.com
References: <0000000000005fe14605b6ea4958@google.com>
 <20201221054031.1468-1-hdanton@sina.com>
From:   Oliver Hartkopp <socketcan@hartkopp.net>
Message-ID: <0f27c47f-b16e-b80e-2fbc-df7894266671@hartkopp.net>
Date:   Mon, 21 Dec 2020 13:55:04 +0100
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Hello Hillf,

On 21.12.20 06:40, Hillf Danton wrote:
> Sun, 20 Dec 2020 11:24:13 -0800
>> syzbot found the following issue on:
>>
>> HEAD commit:    5e60366d Merge tag 'fallthrough-fixes-clang-5.11-rc1' of g..
>> git tree:       upstream
>> console output: https://syzkaller.appspot.com/x/log.txt?x=179a2287500000
>> kernel config:  https://syzkaller.appspot.com/x/.config?x=db720fe37a6a41d8
>> dashboard link: https://syzkaller.appspot.com/bug?extid=78bab6958a614b0c80b9
>> compiler:       gcc (GCC) 10.1.0-syz 20200507
>> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=10ea3e0f500000
>>
>> IMPORTANT: if you fix the issue, please add the following tag to the commit:
>> Reported-by: syzbot+78bab6958a614b0c80b9@syzkaller.appspotmail.com
>>
>> ------------[ cut here ]------------
>> WARNING: CPU: 0 PID: 9908 at net/can/isotp.c:835 isotp_tx_timer_handler+0x65f/0xba0 net/can/isotp.c:835
>> Modules linked in:
>> CPU: 0 PID: 9908 Comm: systemd-udevd Not tainted 5.10.0-syzkaller #0
>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
>> RIP: 0010:isotp_tx_timer_handler+0x65f/0xba0 net/can/isotp.c:835
>> Code: c1 e8 03 83 e1 07 0f b6 04 28 38 c8 7f 08 84 c0 0f 85 b8 04 00 00 41 88 54 24 05 e9 07 fb ff ff 40 84 ed 75 21 e8 21 11 80 f9 <0f> 0b 45 31 e4 e8 17 11 80 f9 44 89 e0 48 83 c4 48 5b 5d 41 5c 41
>> RSP: 0018:ffffc90000007dc8 EFLAGS: 00010246
>> RAX: 0000000000000000 RBX: ffff88803e4e8518 RCX: 0000000000000100
>> RDX: ffff8880117d5040 RSI: ffffffff87f2102f RDI: 0000000000000003
>> RBP: 0000000000000000 R08: ffffffff8a7b6540 R09: ffffffff87f20a2e
>> R10: 0000000000000003 R11: 0000000000000000 R12: 0000000000000000
>> R13: ffff8880b9c26c80 R14: ffff8880b9c26a00 R15: ffff88803e4e8000
>> FS:  00007fc247dbb8c0(0000) GS:ffff8880b9c00000(0000) knlGS:0000000000000000
>> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> CR2: 00007ffcab7e7800 CR3: 000000001c8c6000 CR4: 00000000001506f0
>> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>> Call Trace:
>>   <IRQ>
>>   __run_hrtimer kernel/time/hrtimer.c:1519 [inline]
>>   __hrtimer_run_queues+0x609/0xea0 kernel/time/hrtimer.c:1583
>>   hrtimer_run_softirq+0x17b/0x360 kernel/time/hrtimer.c:1600
>>   __do_softirq+0x2bc/0xa77 kernel/softirq.c:343
>>   asm_call_irq_on_stack+0xf/0x20
>>   </IRQ>
>>   __run_on_irqstack arch/x86/include/asm/irq_stack.h:26 [inline]
>>   run_on_irqstack_cond arch/x86/include/asm/irq_stack.h:77 [inline]
>>   do_softirq_own_stack+0xaa/0xd0 arch/x86/kernel/irq_64.c:77
>>   invoke_softirq kernel/softirq.c:226 [inline]
>>   __irq_exit_rcu+0x17f/0x200 kernel/softirq.c:420
>>   irq_exit_rcu+0x5/0x20 kernel/softirq.c:432
>>   sysvec_apic_timer_interrupt+0x4d/0x100 arch/x86/kernel/apic/apic.c:1096
>>   asm_sysvec_apic_timer_interrupt+0x12/0x20 arch/x86/include/asm/idtentry.h:628
>> RIP: 0010:call_rcu+0x2e7/0x710 kernel/rcu/tree.c:3039
>> Code: 3c 02 00 0f 85 bb 03 00 00 48 8b 05 63 75 1a 0a 49 03 84 24 f0 00 00 00 49 39 c7 0f 8f 72 01 00 00 e8 5d e4 18 00 ff 34 24 9d <48> 83 c4 20 5b 5d 41 5c 41 5d 41 5e 41 5f c3 80 3c 02 00 0f 84 2f
>> RSP: 0018:ffffc9000adafb88 EFLAGS: 00000246
>> RAX: 00000000000010e9 RBX: ffff8880143c1780 RCX: ffffffff815740d7
>> RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
>> RBP: ffff8880b9c35b70 R08: 0000000000000001 R09: ffffffff8f4f983f
>> R10: fffffbfff1e9f307 R11: 0000000000000000 R12: ffff8880b9c35a80
>> R13: ffff8880b9c35b60 R14: ffff8880b9c35b18 R15: 000000000000002c
>>   security_inode_free+0x9a/0xc0 security/security.c:1005
>>   __destroy_inode+0x24d/0x740 fs/inode.c:259
>>   destroy_inode+0x91/0x1b0 fs/inode.c:282
>>   iput_final fs/inode.c:1654 [inline]
>>   iput.part.0+0x41e/0x840 fs/inode.c:1680
>>   iput+0x58/0x70 fs/inode.c:1670
>>   dentry_unlink_inode+0x2b1/0x3d0 fs/dcache.c:374
>>   __dentry_kill+0x3c0/0x640 fs/dcache.c:579
>>   dentry_kill fs/dcache.c:717 [inline]
>>   dput+0x696/0xc10 fs/dcache.c:878
>>   do_renameat2+0xae7/0xbf0 fs/namei.c:4461
>>   __do_sys_rename fs/namei.c:4503 [inline]
>>   __se_sys_rename fs/namei.c:4501 [inline]
>>   __x64_sys_rename+0x5d/0x80 fs/namei.c:4501
>>   do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
>>   entry_SYSCALL_64_after_hwframe+0x44/0xa9
>> RIP: 0033:0x7fc246bb7d47
>> Code: 75 12 48 89 df e8 19 84 07 00 85 c0 0f 95 c0 0f b6 c0 f7 d8 5b c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 b8 52 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 21 41 33 00 f7 d8 64 89 01 48
>> RSP: 002b:00007ffcab6e3c68 EFLAGS: 00000246 ORIG_RAX: 0000000000000052
>> RAX: ffffffffffffffda RBX: 00005556c8f7a380 RCX: 00007fc246bb7d47
>> RDX: 0000000000000000 RSI: 00007ffcab6e3c70 RDI: 00005556c8f823b0
>> RBP: 00007ffcab6e3d30 R08: 00005556c8f812c0 R09: 00005556c8f811e0
>> R10: 00007fc247dbb8c0 R11: 0000000000000246 R12: 00007ffcab6e3c70
>> R13: 0000000000000001 R14: 00005556c71306cb R15: 0000000000000000
> 
> Canceling a running timer that handles ISOTP_WAIT_FC/ISOTP_WAIT_FIRST_FC
> ends up with the so->tx.state assigned to be ISOTP_IDLE.  That triggers
> the warning. Fix it by correcting state before adding timer.
> 
> --- a/net/can/isotp.c
> +++ b/net/can/isotp.c
> @@ -378,6 +378,7 @@ static int isotp_rcv_fc(struct isotp_soc
>   		break;
>   
>   	case ISOTP_FC_WT:
> +		so->tx.state = ISOTP_WAIT_FC;
>   		/* start timer to wait for next FC frame */
>   		hrtimer_start(&so->txtimer, ktime_set(1, 0),
>   			      HRTIMER_MODE_REL_SOFT);
> 

Thanks for looking into this!

But how did you get to this insight?

When going through isotp_rcv_fc() there is no other way than 
so->tx.state already contains ISOTP_WAIT_FC at that point.

Or did I miss something?

Best regards,
Oliver