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

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: fe15c26ee26e Linux 6.3-rc1
git tree: git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci
console output: https://syzkaller.appspot.com/x/log.txt?x=111b3ca4c80000
kernel config: https://syzkaller.appspot.com/x/.config?x=7573cbcd881a88c9
dashboard link: https://syzkaller.appspot.com/bug?extid=e8a22d28d4527d9d6148
compiler: Debian clang version 15.0.7, GNU ld (GNU Binutils for Debian) 2.35.2
userspace arch: arm64
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=160ec3dcc80000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=103d9d42c80000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/89d41abd07bd/disk-fe15c26e.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/fa75f5030ade/vmlinux-fe15c26e.xz
kernel image: https://storage.googleapis.com/syzbot-assets/590d0f5903ee/Image-fe15c26e.gz.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+e8a22d...@syzkaller.appspotmail.com

------------[ cut here ]------------
refcount_t: addition on 0; use-after-free.
WARNING: CPU: 1 PID: 9 at lib/refcount.c:25 refcount_warn_saturate+0x1a8/0x20c lib/refcount.c:25
Modules linked in:
CPU: 1 PID: 9 Comm: kworker/u4:0 Not tainted 6.3.0-rc1-syzkaller-gfe15c26ee26e #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/02/2023
Workqueue: qrtr_ns_handler qrtr_ns_worker
pstate: 604000c5 (nZCv daIF +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
pc : refcount_warn_saturate+0x1a8/0x20c lib/refcount.c:25
lr : refcount_warn_saturate+0x1a8/0x20c lib/refcount.c:25
sp : ffff80001a3a6da0
x29: ffff80001a3a6da0 x28: dfff800000000000 x27: ffff700003474dc8
x26: ffff80001a3a6e60 x25: 0000000000000000 x24: 00000000003a6056
x23: ffff0000d22173f0 x22: 0000000000000000 x21: 0000000000000002
x20: ffff0000d751c098 x19: ffff8000186ee000 x18: ffff80001a3a62a0
x17: 0000000000000000 x16: ffff80001246250c x15: 0000000000000000
x14: 0000000000000000 x13: 0000000000000001 x12: 0000000000000001
x11: ff808000081bd230 x10: 0000000000000000 x9 : 04bb8433d1680a00
x8 : 04bb8433d1680a00 x7 : 0000000000000001 x6 : 0000000000000001
x5 : ffff80001a3a6698 x4 : ffff800015dc52c0 x3 : ffff80000859c514
x2 : 0000000000000001 x1 : 0000000100000001 x0 : 0000000000000000
Call trace:
refcount_warn_saturate+0x1a8/0x20c lib/refcount.c:25
__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+0xdc/0x100 net/qrtr/af_qrtr.c:398
qrtr_send_resume_tx net/qrtr/af_qrtr.c:1003 [inline]
qrtr_recvmsg+0x3dc/0x954 net/qrtr/af_qrtr.c:1070
sock_recvmsg_nosec net/socket.c:1015 [inline]
sock_recvmsg net/socket.c:1036 [inline]
kernel_recvmsg+0x124/0x18c net/socket.c:1061
qrtr_ns_worker+0x294/0x513c net/qrtr/ns.c:688
process_one_work+0x868/0x16f4 kernel/workqueue.c:2390
worker_thread+0x8e0/0xfe8 kernel/workqueue.c:2537
kthread+0x24c/0x2d4 kernel/kthread.c:376
ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:870
irq event stamp: 766220
hardirqs last enabled at (766219): [<ffff800012543b48>] __raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:151 [inline]
hardirqs last enabled at (766219): [<ffff800012543b48>] _raw_spin_unlock_irqrestore+0x44/0xa4 kernel/locking/spinlock.c:194
hardirqs last disabled at (766220): [<ffff80001254393c>] __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:108 [inline]
hardirqs last disabled at (766220): [<ffff80001254393c>] _raw_spin_lock_irqsave+0x2c/0x88 kernel/locking/spinlock.c:162
softirqs last enabled at (766216): [<ffff80001066ca80>] spin_unlock_bh include/linux/spinlock.h:395 [inline]
softirqs last enabled at (766216): [<ffff80001066ca80>] lock_sock_nested+0xe8/0x138 net/core/sock.c:3480
softirqs last disabled at (766214): [<ffff80001066ca28>] spin_lock_bh include/linux/spinlock.h:355 [inline]
softirqs last disabled at (766214): [<ffff80001066ca28>] lock_sock_nested+0x90/0x138 net/core/sock.c:3476
---[ end trace 0000000000000000 ]---


---
This report is generated by a bot. It may contain errors.
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syzbot can test patches for this issue, for details see:
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[Hillf Danton]

On 22 Mar 2023 17:39:54 -0700

> HEAD commit: fe15c26ee26e Linux 6.3-rc1
> git tree: git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci

> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=103d9d42c80000

Replace kref_get() with kref_get_unless_zero() to close race window.

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git fe15c26ee26e

--- x/net/qrtr/af_qrtr.c
+++ y/net/qrtr/af_qrtr.c
@@ -199,7 +199,8 @@ static void __qrtr_node_release(struct k
static struct qrtr_node *qrtr_node_acquire(struct qrtr_node *node)
{
if (node)
- kref_get(&node->ref);
+ if (!kref_get_unless_zero(&node->ref))
+ return NULL;
return node;
}

--

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-and-tested-by: syzbot+e8a22d...@syzkaller.appspotmail.com

Tested on:

commit: fe15c26e Linux 6.3-rc1
git tree: https://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git
console output: https://syzkaller.appspot.com/x/log.txt?x=14783619c80000

kernel config: https://syzkaller.appspot.com/x/.config?x=7573cbcd881a88c9
dashboard link: https://syzkaller.appspot.com/bug?extid=e8a22d28d4527d9d6148
compiler: Debian clang version 15.0.7, GNU ld (GNU Binutils for Debian) 2.35.2
userspace arch: arm64

patch: https://syzkaller.appspot.com/x/patch.diff?x=11d40289c80000

Note: testing is done by a robot and is best-effort only.

[syzbot]

Auto-closing this bug as obsolete.
No recent activity, existing reproducers are no longer triggering the issue.