Subject: WARNING: refcount bug in qrtr_recvmsg

From: syzbot <[email-masked]>
Date: Mon, 07 Sep 2020 14:38:21 -0700

Hello,

syzbot found the following issue on:

HEAD commit:    c70672d8 Merge tag 's390-5.9-5' of git://git.kernel.org/pu..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=163f0c31900000
kernel config:  https://syzkaller.appspot.com/x/.config?x=bd46548257448703
dashboard link: https://syzkaller.appspot.com/bug?extid=d0f27d9af17914bf253b
compiler:       gcc (GCC) 10.1.0-syz 20200507
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=124cc6a5900000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=11436195900000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: [email-masked]

------------[ cut here ]------------
refcount_t: addition on 0; use-after-free.
WARNING: CPU: 0 PID: 118 at lib/refcount.c:25 refcount_warn_saturate+0x169/0x1e0 lib/refcount.c:25
Kernel panic - not syncing: panic_on_warn set ...
CPU: 0 PID: 118 Comm: kworker/u4:3 Not tainted 5.9.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: qrtr_ns_handler qrtr_ns_worker
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x198/0x1fd lib/dump_stack.c:118
 panic+0x347/0x7c0 kernel/panic.c:231
 __warn.cold+0x20/0x46 kernel/panic.c:600
 report_bug+0x1bd/0x210 lib/bug.c:198
 handle_bug+0x38/0x90 arch/x86/kernel/traps.c:234
 exc_invalid_op+0x14/0x40 arch/x86/kernel/traps.c:254
 asm_exc_invalid_op+0x12/0x20 arch/x86/include/asm/idtentry.h:536
RIP: 0010:refcount_warn_saturate+0x169/0x1e0 lib/refcount.c:25
Code: 07 31 ff 89 de e8 e7 df d8 fd 84 db 0f 85 36 ff ff ff e8 9a e3 d8 fd 48 c7 c7 00 dc 93 88 c6 05 67 18 12 07 01 e8 09 e7 a9 fd <0f> 0b e9 17 ff ff ff e8 7b e3 d8 fd 0f b6 1d 4c 18 12 07 31 ff 89
RSP: 0018:ffffc900013479d8 EFLAGS: 00010086
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: ffff8880a8dd4000 RSI: ffffffff815db9a7 RDI: fffff52000268f2d
RBP: 0000000000000002 R08: 0000000000000001 R09: ffff8880ae620f8b
R10: 0000000000000000 R11: 0000000038313154 R12: ffff88821b0f4040
R13: ffff888095619c00 R14: ffff8880a87eb7f0 R15: ffff8880a87eb7f4
 refcount_add include/linux/refcount.h:204 [inline]
 refcount_inc include/linux/refcount.h:241 [inline]
 kref_get include/linux/kref.h:45 [inline]
 qrtr_node_acquire net/qrtr/qrtr.c:196 [inline]
 qrtr_node_lookup net/qrtr/qrtr.c:388 [inline]
 qrtr_send_resume_tx net/qrtr/qrtr.c:980 [inline]
 qrtr_recvmsg+0x845/0x970 net/qrtr/qrtr.c:1043
 sock_recvmsg_nosec net/socket.c:885 [inline]
 sock_recvmsg net/socket.c:903 [inline]
 sock_recvmsg net/socket.c:899 [inline]
 kernel_recvmsg+0x110/0x160 net/socket.c:928
 qrtr_ns_worker+0x15a/0x14fc net/qrtr/ns.c:624
 process_one_work+0x94c/0x1670 kernel/workqueue.c:2269
 worker_thread+0x64c/0x1120 kernel/workqueue.c:2415
 kthread+0x3b5/0x4a0 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294
Shutting down cpus with NMI
Kernel Offset: disabled
Rebooting in 86400 seconds..

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