Re: [syzbot] [arm-msm?] [net?] WARNING: refcount bug in qrtr_recvmsg (2)

[Ziyang Xuan (William)]

> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    9c1bec9c0b08 Merge tag 'linux-kselftest-fixes-6.3-rc3' of ..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=17285724c80000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=6c84f77790aba2eb
> dashboard link: https://syzkaller.appspot.com/bug?extid=a7492efaa5d61b51db23
> compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=13c9f8a4c80000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=10e8fe2cc80000
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/eee5724f97b4/disk-9c1bec9c.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/00ee10c4bc28/vmlinux-9c1bec9c.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/42cf9c3e67cd/bzImage-9c1bec9c.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+a7492efaa5d61b51db23@xxxxxxxxxxxxxxxxxxxxxxxxx
> 
> ------------[ cut here ]------------
> refcount_t: addition on 0; use-after-free.
> WARNING: CPU: 0 PID: 46 at lib/refcount.c:25 refcount_warn_saturate+0x17c/0x1f0 lib/refcount.c:25
> Modules linked in:
> CPU: 0 PID: 46 Comm: kworker/u4:3 Not tainted 6.3.0-rc2-syzkaller-00050-g9c1bec9c0b08 #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/02/2023
> Workqueue: qrtr_ns_handler qrtr_ns_worker
> RIP: 0010:refcount_warn_saturate+0x17c/0x1f0 lib/refcount.c:25
> Code: 0a 31 ff 89 de e8 64 17 73 fd 84 db 0f 85 2e ff ff ff e8 47 1b 73 fd 48 c7 c7 e0 6a a6 8a c6 05 5d 73 52 0a 01 e8 e4 94 3b fd <0f> 0b e9 0f ff ff ff e8 28 1b 73 fd 0f b6 1d 47 73 52 0a 31 ff 89
> RSP: 0018:ffffc90000b779d8 EFLAGS: 00010086
> RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
> RDX: ffff888017d61d40 RSI: ffffffff814b6037 RDI: 0000000000000001
> RBP: ffff88802717ec98 R08: 0000000000000001 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000000 R12: ffff888145178000
> R13: ffff88802717ec00 R14: ffff8880280b1030 R15: ffff8880280b1034
> FS:  0000000000000000(0000) GS:ffff8880b9800000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007ffdb2009388 CR3: 0000000029dad000 CR4: 00000000003506f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  <TASK>
>  __refcount_add include/linux/refcount.h:199 [inline]
>  __refcount_inc include/linux/refcount.h:250 [inline]
>  refcount_inc include/linux/refcount.h:267 [inline]
>  kref_get include/linux/kref.h:45 [inline]
>  qrtr_node_acquire net/qrtr/af_qrtr.c:202 [inline]
>  qrtr_node_lookup net/qrtr/af_qrtr.c:398 [inline]
>  qrtr_send_resume_tx net/qrtr/af_qrtr.c:1003 [inline]
>  qrtr_recvmsg+0x85f/0x990 net/qrtr/af_qrtr.c:1070
>  sock_recvmsg_nosec net/socket.c:1017 [inline]
>  sock_recvmsg+0xe2/0x160 net/socket.c:1038
>  qrtr_ns_worker+0x170/0x1700 net/qrtr/ns.c:688
>  process_one_work+0x991/0x15c0 kernel/workqueue.c:2390
>  worker_thread+0x669/0x1090 kernel/workqueue.c:2537
>  kthread+0x2e8/0x3a0 kernel/kthread.c:376
>  ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:308
>  </TASK>
> 
It occurs in the concurrent scenario of qrtr_recvmsg() and
qrtr_endpoint_unregister() as following:

    cpu0                                        cpu1
qrtr_recvmsg                            qrtr_endpoint_unregister
qrtr_send_resume_tx                     qrtr_node_release
qrtr_node_lookup                        mutex_lock(&qrtr_node_lock)
spin_lock_irqsave(&qrtr_nodes_lock, )   refcount_dec_and_test(&node->ref) [node->ref == 0]
qrtr_node_acquire [node != NULL]        spin_lock_irqsave(&qrtr_nodes_lock, )
kref_get(&node->ref) [WARNING]          __qrtr_node_release
                                        mutex_unlock(&qrtr_node_lock)

and I will give a fix later.

> 
> ---
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> .
>