[PATCH] sysfs: return -ENOENT from move/rename when kobj->sd is NULL

[PATCH] sysfs: return -ENOENT from move/rename when kobj->sd is NULL

[Conor Kotwasinski]

sysfs_move_dir_ns() and sysfs_rename_dir_ns() pass kobj->sd to
kernfs_rename_ns() unconditionally. If sysfs_remove_dir() has already
cleared kobj->sd, the NULL flows through and kernfs_rename_ns()
dereferences it via rcu_access_pointer(kn->__parent), which KASAN
surfaces as a stack-segment fault on the shadow lookup:

  Oops: stack segment: 0000 [#1] SMP KASAN PTI
  RIP: 0010:kernfs_rename_ns+0x3a/0x7a0 fs/kernfs/dir.c:1752
  Call Trace:
   kobject_move+0x525/0x6e0 lib/kobject.c:569
   device_move+0xe0/0x730 drivers/base/core.c:4606
   hci_conn_del_sysfs+0xb8/0x1a0 net/bluetooth/hci_sysfs.c:75
   hci_conn_cleanup net/bluetooth/hci_conn.c:173 [inline]
   hci_conn_del+0xc36/0x1240 net/bluetooth/hci_conn.c:1234
   hci_conn_hash_flush+0x191/0x260 net/bluetooth/hci_conn.c:2638
   hci_dev_close_sync+0x821/0x1100 net/bluetooth/hci_sync.c:5327
   hci_dev_do_close net/bluetooth/hci_core.c:501 [inline]
   hci_unregister_dev+0x21a/0x5b0 net/bluetooth/hci_core.c:2715

syzbot has reported 35 hits with this signature across net, net-next
and linux-next between July 2025 and January 2026, via both vhci
release and HCIDEVRESET ioctl.

Return -ENOENT in that case, consistent with sysfs_create_dir_ns().
The underlying ordering problem in bluetooth -- device_move() called
after the target's sysfs has been torn down -- is a separate issue.

Reported-by: syzbot+d1db96f72a452dc9cbd2@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/all/687c6966.a70a0220.693ce.00a5.GAE@google.com/
Reported-by: syzbot+faeac5b54ba997a96278@syzkaller.appspotmail.com

Signed-off-by: Conor Kotwasinski <conorkotwasinski2024@u.northwestern.edu>
---
 fs/sysfs/dir.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/fs/sysfs/dir.c b/fs/sysfs/dir.c
index ffdcd4153c58..6664fae288c9 100644
--- a/fs/sysfs/dir.c
+++ b/fs/sysfs/dir.c
@@ -108,6 +108,9 @@ int sysfs_rename_dir_ns(struct kobject *kobj, const char *new_name,
 	struct kernfs_node *parent;
 	int ret;
 
+	if (!kobj->sd)
+		return -ENOENT;
+
 	parent = kernfs_get_parent(kobj->sd);
 	ret = kernfs_rename_ns(kobj->sd, parent, new_name, new_ns);
 	kernfs_put(parent);
@@ -120,6 +123,9 @@ int sysfs_move_dir_ns(struct kobject *kobj, struct kobject *new_parent_kobj,
 	struct kernfs_node *kn = kobj->sd;
 	struct kernfs_node *new_parent;
 
+	if (!kn)
+		return -ENOENT;
+
 	new_parent = new_parent_kobj && new_parent_kobj->sd ?
 		new_parent_kobj->sd : sysfs_root_kn;
 
-- 
2.53.0

RE: sysfs: return -ENOENT from move/rename when kobj->sd is NULL

[bluez.test.bot]

[-- Attachment #1: Type: text/plain, Size: 7577 bytes --]

This is automated email and please do not reply to this email!

Dear submitter,

Thank you for submitting the patches to the linux bluetooth mailing list.
This is a CI test results with your patch series:
PW Link:https://patchwork.kernel.org/project/bluetooth/list/?series=1082102

---Test result---

Test Summary:
CheckPatch                    FAIL      0.66 seconds
GitLint                       PASS      0.29 seconds
SubjectPrefix                 FAIL      0.11 seconds
BuildKernel                   PASS      24.72 seconds
CheckAllWarning               PASS      27.23 seconds
CheckSparse                   PASS      26.09 seconds
BuildKernel32                 PASS      24.07 seconds
TestRunnerSetup               PASS      517.22 seconds
TestRunner_l2cap-tester       PASS      27.33 seconds
TestRunner_iso-tester         PASS      45.68 seconds
TestRunner_bnep-tester        PASS      6.25 seconds
TestRunner_mgmt-tester        FAIL      111.08 seconds
TestRunner_rfcomm-tester      PASS      9.47 seconds
TestRunner_sco-tester         FAIL      13.81 seconds
TestRunner_ioctl-tester       PASS      10.27 seconds
TestRunner_mesh-tester        FAIL      11.21 seconds
TestRunner_smp-tester         PASS      8.52 seconds
TestRunner_userchan-tester    PASS      6.56 seconds
TestRunner_6lowpan-tester     FAIL      8.38 seconds
IncrementalBuild              PASS      23.77 seconds

Details
##############################
Test: CheckPatch - FAIL
Desc: Run checkpatch.pl script
Output:
sysfs: return -ENOENT from move/rename when kobj->sd is NULL
WARNING: Reported-by: should be immediately followed by Closes: with a URL to the report
#136: 
Reported-by: syzbot+faeac5b54ba997a96278@syzkaller.appspotmail.com


WARNING: The commit message has 'syzkaller', perhaps it also needs a 'Fixes:' tag?

total: 0 errors, 2 warnings, 18 lines checked

NOTE: For some of the reported defects, checkpatch may be able to
      mechanically convert to the typical style using --fix or --fix-inplace.

/github/workspace/src/patch/14527101.patch has style problems, please review.

NOTE: Ignored message types: UNKNOWN_COMMIT_ID

NOTE: If any of the errors are false positives, please report
      them to the maintainer, see CHECKPATCH in MAINTAINERS.


##############################
Test: SubjectPrefix - FAIL
Desc: Check subject contains "Bluetooth" prefix
Output:
"Bluetooth: " prefix is not specified in the subject
##############################
Test: TestRunner_mgmt-tester - FAIL
Desc: Run mgmt-tester with test-runner
Output:
Total: 494, Passed: 489 (99.0%), Failed: 1, Not Run: 4

Failed Test Cases
Read Exp Feature - Success                           Failed       0.102 seconds
##############################
Test: TestRunner_sco-tester - FAIL
Desc: Run sco-tester with test-runner
Output:
WARNING: possible circular locking dependency detected
7.0.0-rc2-gfc81722c1c6d #1 Not tainted
------------------------------------------------------
kworker/u5:2/117 is trying to acquire lock:
ffff88800207e240 (sk_lock-AF_BLUETOOTH-BTPROTO_SCO){+.+.}-{0:0}, at: sco_connect_cfm+0x358/0x8d0

but task is already holding lock:
ffff888002141c20 (&conn->lock){+.+.}-{3:3}, at: sco_connect_cfm+0x22d/0x8d0

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (&conn->lock){+.+.}-{3:3}:
       lock_acquire+0xf7/0x2c0
       _raw_spin_lock+0x2a/0x40
       sco_sock_connect+0x4d7/0x1280
       __sys_connect+0x1a3/0x260
       __x64_sys_connect+0x6e/0xb0
       do_syscall_64+0xa0/0x570
       entry_SYSCALL_64_after_hwframe+0x74/0x7c

-> #0 (sk_lock-AF_BLUETOOTH-BTPROTO_SCO){+.+.}-{0:0}:
       check_prev_add+0xe9/0xc70
       __lock_acquire+0x1457/0x1df0
       lock_acquire+0xf7/0x2c0
       lock_sock_nested+0x36/0xd0
       sco_connect_cfm+0x358/0x8d0
       hci_sync_conn_complete_evt+0x3d3/0x8e0
       hci_event_packet+0x74f/0xb10
       hci_rx_work+0x398/0xd00
       process_scheduled_works+0xb16/0x1ac0
       worker_thread+0x4ff/0xba0
       kthread+0x368/0x490
       ret_from_fork+0x498/0x7e0
       ret_from_fork_asm+0x19/0x30

other info that might help us debug this:

...
BUG: sleeping function called from invalid context at net/core/sock.c:3782
in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 117, name: kworker/u5:2
preempt_count: 1, expected: 0
RCU nest depth: 0, expected: 0
INFO: lockdep is turned off.
CPU: 0 UID: 0 PID: 117 Comm: kworker/u5:2 Not tainted 7.0.0-rc2-gfc81722c1c6d #1 PREEMPT(lazy) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.13.0-1ubuntu1.1 04/01/2014
Workqueue: hci0 hci_rx_work
Call Trace:
 <TASK>
 dump_stack_lvl+0x49/0x60
 __might_resched+0x2ea/0x500
 lock_sock_nested+0x47/0xd0
 ? sco_connect_cfm+0x358/0x8d0
 sco_connect_cfm+0x358/0x8d0
 ? hci_debugfs_create_conn+0x190/0x210
 ? __pfx_sco_connect_cfm+0x10/0x10
 hci_sync_conn_complete_evt+0x3d3/0x8e0
 hci_event_packet+0x74f/0xb10
 ? __pfx_hci_sync_conn_complete_evt+0x10/0x10
 ? __pfx_hci_event_packet+0x10/0x10
 ? mark_held_locks+0x49/0x80
 ? lockdep_hardirqs_on_prepare+0xd4/0x180
 ? _raw_spin_unlock_irqrestore+0x2c/0x50
 hci_rx_work+0x398/0xd00
 process_scheduled_works+0xb16/0x1ac0
 ? __pfx_process_scheduled_works+0x10/0x10
 ? lock_acquire+0xf7/0x2c0
 ? lock_is_held_type+0x9b/0x110
 ? __pfx_hci_rx_work+0x10/0x10
 worker_thread+0x4ff/0xba0
 ? _raw_spin_unlock_irqrestore+0x2c/0x50
 ? __pfx_worker_thread+0x10/0x10
 kthread+0x368/0x490
 ? _raw_spin_unlock_irq+0x23/0x40
 ? __pfx_kthread+0x10/0x10
 ret_from_fork+0x498/0x7e0
 ? __pfx_ret_from_fork+0x10/0x10
 ? __switch_to+0x9e4/0xe50
 ? __switch_to_asm+0x32/0x60
...
Total: 30, Passed: 30 (100.0%), Failed: 0, Not Run: 0
##############################
Test: TestRunner_mesh-tester - FAIL
Desc: Run mesh-tester with test-runner
Output:
Total: 10, Passed: 8 (80.0%), Failed: 2, Not Run: 0

Failed Test Cases
Mesh - Send cancel - 1                               Timed out    1.895 seconds
Mesh - Send cancel - 2                               Timed out    1.995 seconds
##############################
Test: TestRunner_6lowpan-tester - FAIL
Desc: Run 6lowpan-tester with test-runner
Output:
WARNING: possible circular locking dependency detected
7.0.0-rc2-gfc81722c1c6d #1 Not tainted
------------------------------------------------------
kworker/0:0/9 is trying to acquire lock:
ffff888002754140 ((wq_completion)hci0#2){+.+.}-{0:0}, at: touch_wq_lockdep_map+0x75/0x180

but task is already holding lock:
ffffffffade4d720 (rtnl_mutex){+.+.}-{4:4}, at: lowpan_unregister_netdev+0xd/0x30

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #4 (rtnl_mutex){+.+.}-{4:4}:
       lock_acquire+0xf7/0x2c0
       __mutex_lock+0x16b/0x1fc0
       lowpan_register_netdev+0x11/0x30
       chan_ready_cb+0x836/0xd00
       l2cap_recv_frame+0x6a06/0x8920
       l2cap_recv_acldata+0x790/0xdf0
       hci_rx_work+0x500/0xd00
       process_scheduled_works+0xb16/0x1ac0
       worker_thread+0x4ff/0xba0
       kthread+0x368/0x490
       ret_from_fork+0x498/0x7e0
       ret_from_fork_asm+0x19/0x30

-> #3 (&chan->lock#3/1){+.+.}-{4:4}:
       lock_acquire+0xf7/0x2c0
       __mutex_lock+0x16b/0x1fc0
       l2cap_chan_connect+0x74e/0x1980
       lowpan_control_write+0x523/0x660
       full_proxy_write+0x10b/0x190
       vfs_write+0x1c0/0xf60
       ksys_write+0xf1/0x1d0
       do_syscall_64+0xa0/0x570
       entry_SYSCALL_64_after_hwframe+0x74/0x7c

-> #2 (&conn->lock){+.+.}-{4:4}:
...
Total: 8, Passed: 8 (100.0%), Failed: 0, Not Run: 0


https://github.com/bluez/bluetooth-next/pull/94

---
Regards,
Linux Bluetooth