netdev - Re: [syzbot] WARNING in batadv_nc_mesh

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Date:   Fri, 22 Oct 2021 21:33:47 +0300
From:   Pavel Skripkin <paskripkin@...il.com>
To:     syzbot <syzbot+28b0702ada0bf7381f58@...kaller.appspotmail.com>,
        a@...table.cc, b.a.t.m.a.n@...ts.open-mesh.org,
        davem@...emloft.net, kuba@...nel.org, linux-kernel@...r.kernel.org,
        mareklindner@...mailbox.ch, netdev@...r.kernel.org,
        sven@...fation.org, sw@...onwunderlich.de,
        syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] WARNING in batadv_nc_mesh_free

On 10/22/21 02:19, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    2f111a6fd5b5 Merge tag 'ceph-for-5.15-rc7' of git://github..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=115750acb00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=d95853dad8472c91
> dashboard link: https://syzkaller.appspot.com/bug?extid=28b0702ada0bf7381f58
> compiler:       Debian clang version 11.0.1-2, GNU ld (GNU Binutils for Debian) 2.35.2
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1026ef2cb00000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=15c9c162b00000
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+28b0702ada0bf7381f58@...kaller.appspotmail.com
> 
> RBP: 00007ffef262e230 R08: 0000000000000002 R09: 00007fddc8003531
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000004
> R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
> ------------[ cut here ]------------
> ODEBUG: assert_init not available (active state 0) object type: timer_list hint: 0x0
> WARNING: CPU: 0 PID: 6517 at lib/debugobjects.c:508 debug_print_object lib/debugobjects.c:505 [inline]
> WARNING: CPU: 0 PID: 6517 at lib/debugobjects.c:508 debug_object_assert_init+0x1fa/0x250 lib/debugobjects.c:895
> Modules linked in:
> CPU: 0 PID: 6517 Comm: syz-executor011 Not tainted 5.15.0-rc6-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> RIP: 0010:debug_print_object lib/debugobjects.c:505 [inline]
> RIP: 0010:debug_object_assert_init+0x1fa/0x250 lib/debugobjects.c:895
> Code: e8 4b 15 b8 fd 4c 8b 45 00 48 c7 c7 a0 31 b4 8a 48 c7 c6 00 2e b4 8a 48 c7 c2 e0 33 b4 8a 31 c9 49 89 d9 31 c0 e8 b6 c6 36 fd <0f> 0b ff 05 3a 5c c5 09 48 83 c5 38 48 89 e8 48 c1 e8 03 42 80 3c
> RSP: 0018:ffffc90002c7e698 EFLAGS: 00010046
> RAX: cffa606352c78700 RBX: 0000000000000000 RCX: ffff888076ce9c80
> RDX: 0000000000000000 RSI: 0000000080000000 RDI: 0000000000000000
> RBP: ffffffff8a512d00 R08: ffffffff81693402 R09: ffffed1017383f2c
> R10: ffffed1017383f2c R11: 0000000000000000 R12: dffffc0000000000
> R13: ffff88801bcd1720 R14: 0000000000000002 R15: ffffffff90ba5a20
> FS:  0000555557087300(0000) GS:ffff8880b9c00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007f5473f3c000 CR3: 0000000070ca6000 CR4: 00000000003506f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>   debug_timer_assert_init kernel/time/timer.c:739 [inline]
>   debug_assert_init kernel/time/timer.c:784 [inline]
>   del_timer+0xa5/0x3d0 kernel/time/timer.c:1204
>   try_to_grab_pending+0x151/0xbb0 kernel/workqueue.c:1270
>   __cancel_work_timer+0x14c/0x710 kernel/workqueue.c:3129
>   batadv_nc_mesh_free+0x4a/0xf0 net/batman-adv/network-coding.c:1869
>   batadv_mesh_free+0x6f/0x140 net/batman-adv/main.c:245
>   batadv_mesh_init+0x4e5/0x550 net/batman-adv/main.c:226

Looks like cancel_delayed_work_sync() is called before 
INIT_DELAYED_WORK(), so calltrace looks like

batadv_mesh_init()
   batadv_originator_init()  <- injected allocation failure
   batadv_mesh_free()
     batadv_nc_mesh_free()
       cancel_delayed_work_sync()


Quick fix can be moving INIT_DELAYED_WORK() from batadv_nc_init() to 
batadv_mesh_init(), since there is complex dependencies between each 
mech part, if I understood comments correctly


Just for thoughts and syzbot testing

#syz test
git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master



With regards,
Pavel Skripkin



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