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* [PATCH] Bluetooth: L2CAP: Fix use-after-free in l2cap_unregister_user
@ 2025-11-05 14:22 ssrane_b23
  2025-11-05 14:40 ` shaurya
                   ` (3 more replies)
  0 siblings, 4 replies; 23+ messages in thread
From: ssrane_b23 @ 2025-11-05 14:22 UTC (permalink / raw)
  To: marcel
  Cc: johan.hedberg, luiz.dentz, linux-bluetooth, linux-kernel,
	syzbot+14b6d57fb728e27ce23c, linux-kernel-mentees, skhan,
	david.hunter.linux, khalid, Shaurya Rane

From: Shaurya Rane <ssrane_b23@ee.vjti.ac.in>

Syzbot reported a use-after-free in l2cap_unregister_user(), caused by
missing reference counting on the associated hci_dev. If the device is
unregistered while L2CAP users are still active, l2cap_unregister_user()
may access a freed hci_dev when taking its lock.

Fix this by taking a device reference in l2cap_register_user() using
hci_dev_hold(), and releasing it in l2cap_unregister_user() via
hci_dev_put(). This ensures the hci_dev remains valid for the lifetime
of registered L2CAP users.

Reported-by: syzbot+14b6d57fb728e27ce23c@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=14b6d57fb728e27ce23c
Fixes: c8992cffbe74 ("Bluetooth: hci_event: Use of a function table to handle Command Complete")
Signed-off-by: Shaurya Rane <ssrane_b23@ee.vjti.ac.in>
---
 net/bluetooth/l2cap_core.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
index 805c752ac0a9..6a880f8ab6c2 100644
--- a/net/bluetooth/l2cap_core.c
+++ b/net/bluetooth/l2cap_core.c
@@ -1688,6 +1688,11 @@ int l2cap_register_user(struct l2cap_conn *conn, struct l2cap_user *user)
 	struct hci_dev *hdev = conn->hcon->hdev;
 	int ret;
 
+	/* Hold a reference to hdev to prevent it from being freed while
+	 * we have registered users.
+	 */
+	hci_dev_hold(hdev);
+
 	/* We need to check whether l2cap_conn is registered. If it is not, we
 	 * must not register the l2cap_user. l2cap_conn_del() is unregisters
 	 * l2cap_conn objects, but doesn't provide its own locking. Instead, it
@@ -1717,6 +1722,10 @@ int l2cap_register_user(struct l2cap_conn *conn, struct l2cap_user *user)
 
 out_unlock:
 	hci_dev_unlock(hdev);
+
+	if (ret)
+		hci_dev_put(hdev);
+
 	return ret;
 }
 EXPORT_SYMBOL(l2cap_register_user);
@@ -1735,6 +1744,9 @@ void l2cap_unregister_user(struct l2cap_conn *conn, struct l2cap_user *user)
 
 out_unlock:
 	hci_dev_unlock(hdev);
+
+	/* Release the reference we took in l2cap_register_user */
+	hci_dev_put(hdev);
 }
 EXPORT_SYMBOL(l2cap_unregister_user);
 
-- 
2.34.1


^ permalink raw reply related	[flat|nested] 23+ messages in thread
* Re: [RESEND] Bluetooth: L2CAP: Fix use-after-free in l2cap_unregister_user
  2026-03-07  9:45 [RESEND] Bluetooth: L2CAP: Fix use-after-free " Pauli Virtanen
@ 2026-03-07 10:32 Pauli Virtanen
  2026-03-07 11:00 ` [syzbot] [bluetooth?] KASAN: slab-use-after-free Read " syzbot
  0 siblings, 1 reply; 23+ messages in thread
From: Pauli Virtanen @ 2026-03-07 10:32 UTC (permalink / raw)
  To: linux-bluetooth; +Cc: syzbot+14b6d57fb728e27ce23c

[-- Attachment #1: Type: text/plain, Size: 4508 bytes --]

la, 2026-03-07 kello 11:45 +0200, Pauli Virtanen kirjoitti:
> la, 2026-03-07 kello 10:59 +0200, Pauli Virtanen kirjoitti:
> > pe, 2026-03-06 kello 16:04 -0500, Luiz Augusto von Dentz kirjoitti:
> > > From: Shaurya Rane <ssrane_b23@ee.vjti.ac.in>
> > > 
> > > After commit ab4eedb790ca ("Bluetooth: L2CAP: Fix corrupted list in
> > > hci_chan_del"), l2cap_conn_del() uses conn->lock to protect access to
> > > conn->users and conn->hchan. However, l2cap_register_user() and
> > > l2cap_unregister_user() still use hci_dev_lock(), creating a race
> > > condition where these functions can access conn->users and conn->hchan
> > > concurrently with l2cap_conn_del().
> > 
> > AFAIK the above text from the original submitter is a bit inaccurate,
> > as l2cap_conn_del() is called with hdev lock held, so conn->users/hchan
> > should be safe.
> > 
> > However, using conn->mutex should fix the use-after-free in
> > 
> > 	conn->hcon->hdev
> > 	hci_dev_lock(hdev);
> > 	hci_dev_unlock(hdev);
> > 
> > by making l2cap_unregister_user() safe to call after the hcon/hdev are
> > no longer alive.
> > 
> > The change looks OK to me, but probably worth to double check with
> > syzbot it fixes the original issue
> 
> syzbot seems to have hit some internal error, another try on upstream
> branch instead
> 

No luck, test the patch setting session->conn = NULL; in case it fixes
the syzcaller failure. If that passes, maybe the conn->mutex locking
overlooks something that I don't see right now,

#syz test

> > > This can lead to use-after-free and list corruption bugs, as reported
> > > by syzbot.
> > > 
> > > Fix this by changing l2cap_register_user() and l2cap_unregister_user()
> > > to use conn->lock instead of hci_dev_lock(), ensuring consistent locking
> > > for the l2cap_conn structure.
> > > Reported-by: syzbot+14b6d57fb728e27ce23c@syzkaller.appspotmail.com
> > > Closes: https://syzkaller.appspot.com/bug?extid=14b6d57fb728e27ce23c
> > > Fixes: ab4eedb790ca ("Bluetooth: L2CAP: Fix corrupted list in hci_chan_del")
> > > Signed-off-by: Shaurya Rane <ssrane_b23@ee.vjti.ac.in>
> > > Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
> > > ---
> > >  net/bluetooth/l2cap_core.c | 20 ++++++++------------
> > >  1 file changed, 8 insertions(+), 12 deletions(-)
> > > 
> > > diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
> > > index 14131e427efd..6606d7f12534 100644
> > > --- a/net/bluetooth/l2cap_core.c
> > > +++ b/net/bluetooth/l2cap_core.c
> > > @@ -1678,17 +1678,15 @@ static void l2cap_info_timeout(struct work_struct *work)
> > >  
> > >  int l2cap_register_user(struct l2cap_conn *conn, struct l2cap_user *user)
> > >  {
> > > -	struct hci_dev *hdev = conn->hcon->hdev;
> > >  	int ret;
> > >  
> > >  	/* We need to check whether l2cap_conn is registered. If it is not, we
> > > -	 * must not register the l2cap_user. l2cap_conn_del() is unregisters
> > > -	 * l2cap_conn objects, but doesn't provide its own locking. Instead, it
> > > -	 * relies on the parent hci_conn object to be locked. This itself relies
> > > -	 * on the hci_dev object to be locked. So we must lock the hci device
> > > -	 * here, too. */
> > > +	 * must not register the l2cap_user. l2cap_conn_del() unregisters
> > > +	 * l2cap_conn objects under conn->lock, and we use the same lock here
> > > +	 * to protect access to conn->users and conn->hchan.
> > > +	 */
> > >  
> > > -	hci_dev_lock(hdev);
> > > +	mutex_lock(&conn->lock);
> > >  
> > >  	if (!list_empty(&user->list)) {
> > >  		ret = -EINVAL;
> > > @@ -1709,16 +1707,14 @@ int l2cap_register_user(struct l2cap_conn *conn, struct l2cap_user *user)
> > >  	ret = 0;
> > >  
> > >  out_unlock:
> > > -	hci_dev_unlock(hdev);
> > > +	mutex_unlock(&conn->lock);
> > >  	return ret;
> > >  }
> > >  EXPORT_SYMBOL(l2cap_register_user);
> > >  
> > >  void l2cap_unregister_user(struct l2cap_conn *conn, struct l2cap_user *user)
> > >  {
> > > -	struct hci_dev *hdev = conn->hcon->hdev;
> > > -
> > > -	hci_dev_lock(hdev);
> > > +	mutex_lock(&conn->lock);
> > >  
> > >  	if (list_empty(&user->list))
> > >  		goto out_unlock;
> > > @@ -1727,7 +1723,7 @@ void l2cap_unregister_user(struct l2cap_conn *conn, struct l2cap_user *user)
> > >  	user->remove(conn, user);
> > >  
> > >  out_unlock:
> > > -	hci_dev_unlock(hdev);
> > > +	mutex_unlock(&conn->lock);
> > >  }
> > >  EXPORT_SYMBOL(l2cap_unregister_user);
> > >  

[-- Attachment #2: 0001-Bluetooth-HIDP-Fix-possible-UAF.patch --]
[-- Type: text/x-patch, Size: 15843 bytes --]

From 9d7d765a35c2385fe0c387199e484f486e6f2257 Mon Sep 17 00:00:00 2001
Message-ID: <9d7d765a35c2385fe0c387199e484f486e6f2257.1772879270.git.pav@iki.fi>
From: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Date: Thu, 5 Mar 2026 10:17:47 -0500
Subject: [PATCH] Bluetooth: HIDP: Fix possible UAF
To: linux-bluetooth@vger.kernel.org

This fixes the following trace caused by not dropping l2cap_conn
reference when user->remove callback is called:

[   97.809249] l2cap_conn_free: freeing conn ffff88810a171c00
[   97.809907] CPU: 1 UID: 0 PID: 1419 Comm: repro_standalon Not tainted 7.0.0-rc1-dirty #14 PREEMPT(lazy)
[   97.809935] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.17.0-debian-1.17.0-1 04/01/2014
[   97.809947] Call Trace:
[   97.809954]  <TASK>
[   97.809961]  dump_stack_lvl (lib/dump_stack.c:122)
[   97.809990]  l2cap_conn_free (net/bluetooth/l2cap_core.c:1808)
[   97.810017]  l2cap_conn_del (./include/linux/kref.h:66 net/bluetooth/l2cap_core.c:1821 net/bluetooth/l2cap_core.c:1798)
[   97.810055]  l2cap_disconn_cfm (net/bluetooth/l2cap_core.c:7347 (discriminator 1) net/bluetooth/l2cap_core.c:7340 (discriminator 1))
[   97.810086]  ? __pfx_l2cap_disconn_cfm (net/bluetooth/l2cap_core.c:7341)
[   97.810117]  hci_conn_hash_flush (./include/net/bluetooth/hci_core.h:2152 (discriminator 2) net/bluetooth/hci_conn.c:2644 (discriminator 2))
[   97.810148]  hci_dev_close_sync (net/bluetooth/hci_sync.c:5360)
[   97.810180]  ? __pfx_hci_dev_close_sync (net/bluetooth/hci_sync.c:5285)
[   97.810212]  ? srso_alias_return_thunk (arch/x86/lib/retpoline.S:221)
[   97.810242]  ? up_write (./arch/x86/include/asm/atomic64_64.h:87 (discriminator 5) ./include/linux/atomic/atomic-arch-fallback.h:2852 (discriminator 5) ./include/linux/atomic/atomic-long.h:268 (discriminator 5) ./include/linux/atomic/atomic-instrumented.h:3391 (discriminator 5) kernel/locking/rwsem.c:1385 (discriminator 5) kernel/locking/rwsem.c:1643 (discriminator 5))
[   97.810267]  ? srso_alias_return_thunk (arch/x86/lib/retpoline.S:221)
[   97.810290]  ? rcu_is_watching (./arch/x86/include/asm/atomic.h:23 ./include/linux/atomic/atomic-arch-fallback.h:457 ./include/linux/context_tracking.h:128 kernel/rcu/tree.c:752)
[   97.810320]  hci_unregister_dev (net/bluetooth/hci_core.c:504 net/bluetooth/hci_core.c:2716)
[   97.810346]  vhci_release (drivers/bluetooth/hci_vhci.c:691)
[   97.810375]  ? __pfx_vhci_release (drivers/bluetooth/hci_vhci.c:678)
[   97.810404]  __fput (fs/file_table.c:470)
[   97.810430]  task_work_run (kernel/task_work.c:235)
[   97.810451]  ? __pfx_task_work_run (kernel/task_work.c:201)
[   97.810472]  ? srso_alias_return_thunk (arch/x86/lib/retpoline.S:221)
[   97.810495]  ? do_raw_spin_unlock (./include/asm-generic/qspinlock.h:128 (discriminator 5) kernel/locking/spinlock_debug.c:142 (discriminator 5))
[   97.810527]  do_exit (kernel/exit.c:972)
[   97.810547]  ? srso_alias_return_thunk (arch/x86/lib/retpoline.S:221)
[   97.810574]  ? __pfx_do_exit (kernel/exit.c:897)
[   97.810594]  ? lock_acquire (kernel/locking/lockdep.c:470 (discriminator 6) kernel/locking/lockdep.c:5870 (discriminator 6) kernel/locking/lockdep.c:5825 (discriminator 6))
[   97.810616]  ? srso_alias_return_thunk (arch/x86/lib/retpoline.S:221)
[   97.810639]  ? do_raw_spin_lock (kernel/locking/spinlock_debug.c:95 (discriminator 4) kernel/locking/spinlock_debug.c:118 (discriminator 4))
[   97.810664]  ? srso_alias_return_thunk (arch/x86/lib/retpoline.S:221)
[   97.810688]  ? find_held_lock (kernel/locking/lockdep.c:5350 (discriminator 1))
[   97.810721]  do_group_exit (kernel/exit.c:1093)
[   97.810745]  get_signal (kernel/signal.c:3007 (discriminator 1))
[   97.810772]  ? security_file_permission (./arch/x86/include/asm/jump_label.h:37 security/security.c:2366)
[   97.810803]  ? srso_alias_return_thunk (arch/x86/lib/retpoline.S:221)
[   97.810826]  ? vfs_read (fs/read_write.c:555)
[   97.810854]  ? __pfx_get_signal (kernel/signal.c:2800)
[   97.810880]  ? srso_alias_return_thunk (arch/x86/lib/retpoline.S:221)
[   97.810905]  ? __pfx_vfs_read (fs/read_write.c:555)
[   97.810932]  ? srso_alias_return_thunk (arch/x86/lib/retpoline.S:221)
[   97.810960]  arch_do_signal_or_restart (arch/x86/kernel/signal.c:337 (discriminator 1))
[   97.810990]  ? __pfx_arch_do_signal_or_restart (arch/x86/kernel/signal.c:334)
[   97.811021]  ? srso_alias_return_thunk (arch/x86/lib/retpoline.S:221)
[   97.811055]  ? srso_alias_return_thunk (arch/x86/lib/retpoline.S:221)
[   97.811078]  ? ksys_read (fs/read_write.c:707)
[   97.811106]  ? __pfx_ksys_read (fs/read_write.c:707)
[   97.811137]  exit_to_user_mode_loop (kernel/entry/common.c:66 kernel/entry/common.c:98)
[   97.811169]  ? rcu_is_watching (./arch/x86/include/asm/atomic.h:23 ./include/linux/atomic/atomic-arch-fallback.h:457 ./include/linux/context_tracking.h:128 kernel/rcu/tree.c:752)
[   97.811192]  ? srso_alias_return_thunk (arch/x86/lib/retpoline.S:221)
[   97.811215]  ? trace_hardirqs_off (./include/trace/events/preemptirq.h:36 (discriminator 33) kernel/trace/trace_preemptirq.c:95 (discriminator 33) kernel/trace/trace_preemptirq.c:90 (discriminator 33))
[   97.811240]  do_syscall_64 (./include/linux/irq-entry-common.h:226 ./include/linux/irq-entry-common.h:256 ./include/linux/entry-common.h:325 arch/x86/entry/syscall_64.c:100)
[   97.811268]  ? srso_alias_return_thunk (arch/x86/lib/retpoline.S:221)
[   97.811292]  ? exc_page_fault (arch/x86/mm/fault.c:1480 (discriminator 3) arch/x86/mm/fault.c:1527 (discriminator 3))
[   97.811318]  entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130)
[   97.811338] RIP: 0033:0x445cfe
[   97.811352] Code: Unable to access opcode bytes at 0x445cd4.

Code starting with the faulting instruction
===========================================
[   97.811360] RSP: 002b:00007f65c41c6dc8 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
[   97.811378] RAX: fffffffffffffe00 RBX: 00007f65c41c76c0 RCX: 0000000000445cfe
[   97.811391] RDX: 0000000000000400 RSI: 00007f65c41c6e40 RDI: 0000000000000004
[   97.811403] RBP: 00007f65c41c7250 R08: 0000000000000000 R09: 0000000000000000
[   97.811415] R10: 0000000000000000 R11: 0000000000000246 R12: ffffffffffffffe8
[   97.811428] R13: 0000000000000000 R14: 00007fff780a8c00 R15: 00007f65c41c76c0
[   97.811453]  </TASK>
[   98.402453] ==================================================================
[   98.403560] BUG: KASAN: use-after-free in __mutex_lock (kernel/locking/mutex.c:199 kernel/locking/mutex.c:694 kernel/locking/mutex.c:776)
[   98.404541] Read of size 8 at addr ffff888113ee40a8 by task khidpd_00050004/1430
[   98.405361]
[   98.405563] CPU: 1 UID: 0 PID: 1430 Comm: khidpd_00050004 Not tainted 7.0.0-rc1-dirty #14 PREEMPT(lazy)
[   98.405588] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.17.0-debian-1.17.0-1 04/01/2014
[   98.405600] Call Trace:
[   98.405607]  <TASK>
[   98.405614]  dump_stack_lvl (lib/dump_stack.c:122)
[   98.405641]  print_report (mm/kasan/report.c:379 mm/kasan/report.c:482)
[   98.405667]  ? srso_alias_return_thunk (arch/x86/lib/retpoline.S:221)
[   98.405691]  ? __virt_addr_valid (arch/x86/mm/physaddr.c:55)
[   98.405724]  ? __mutex_lock (kernel/locking/mutex.c:199 kernel/locking/mutex.c:694 kernel/locking/mutex.c:776)
[   98.405748]  kasan_report (mm/kasan/report.c:221 mm/kasan/report.c:597)
[   98.405778]  ? __mutex_lock (kernel/locking/mutex.c:199 kernel/locking/mutex.c:694 kernel/locking/mutex.c:776)
[   98.405807]  __mutex_lock (kernel/locking/mutex.c:199 kernel/locking/mutex.c:694 kernel/locking/mutex.c:776)
[   98.405832]  ? do_raw_spin_lock (kernel/locking/spinlock_debug.c:95 (discriminator 4) kernel/locking/spinlock_debug.c:118 (discriminator 4))
[   98.405859]  ? l2cap_unregister_user (./include/linux/list.h:381 (discriminator 2) net/bluetooth/l2cap_core.c:1723 (discriminator 2))
[   98.405888]  ? __pfx_do_raw_spin_lock (kernel/locking/spinlock_debug.c:114)
[   98.405915]  ? __pfx___mutex_lock (kernel/locking/mutex.c:775)
[   98.405939]  ? srso_alias_return_thunk (arch/x86/lib/retpoline.S:221)
[   98.405963]  ? lock_acquire (kernel/locking/lockdep.c:470 (discriminator 6) kernel/locking/lockdep.c:5870 (discriminator 6) kernel/locking/lockdep.c:5825 (discriminator 6))
[   98.405984]  ? find_held_lock (kernel/locking/lockdep.c:5350 (discriminator 1))
[   98.406015]  ? srso_alias_return_thunk (arch/x86/lib/retpoline.S:221)
[   98.406038]  ? lock_release (kernel/locking/lockdep.c:5536 kernel/locking/lockdep.c:5889 kernel/locking/lockdep.c:5875)
[   98.406061]  ? srso_alias_return_thunk (arch/x86/lib/retpoline.S:221)
[   98.406085]  ? _raw_spin_unlock_irqrestore (./arch/x86/include/asm/irqflags.h:42 ./arch/x86/include/asm/irqflags.h:119 ./arch/x86/include/asm/irqflags.h:159 ./include/linux/spinlock_api_smp.h:178 kernel/locking/spinlock.c:194)
[   98.406107]  ? srso_alias_return_thunk (arch/x86/lib/retpoline.S:221)
[   98.406130]  ? __timer_delete_sync (kernel/time/timer.c:1592)
[   98.406158]  ? l2cap_unregister_user (./include/linux/list.h:381 (discriminator 2) net/bluetooth/l2cap_core.c:1723 (discriminator 2))
[   98.406186]  ? srso_alias_return_thunk (arch/x86/lib/retpoline.S:221)
[   98.406210]  l2cap_unregister_user (./include/linux/list.h:381 (discriminator 2) net/bluetooth/l2cap_core.c:1723 (discriminator 2))
[   98.406263]  hidp_session_thread (./include/linux/instrumented.h:112 ./include/linux/atomic/atomic-instrumented.h:400 ./include/linux/refcount.h:389 ./include/linux/refcount.h:432 ./include/linux/refcount.h:450 ./include/linux/kref.h:64 net/bluetooth/hidp/core.c:996 net/bluetooth/hidp/core.c:1305)
[   98.406293]  ? __pfx_hidp_session_thread (net/bluetooth/hidp/core.c:1264)
[   98.406323]  ? kthread (kernel/kthread.c:433)
[   98.406340]  ? __pfx_hidp_session_wake_function (net/bluetooth/hidp/core.c:1251)
[   98.406370]  ? srso_alias_return_thunk (arch/x86/lib/retpoline.S:221)
[   98.406393]  ? find_held_lock (kernel/locking/lockdep.c:5350 (discriminator 1))
[   98.406424]  ? __pfx_hidp_session_wake_function (net/bluetooth/hidp/core.c:1251)
[   98.406453]  ? srso_alias_return_thunk (arch/x86/lib/retpoline.S:221)
[   98.406476]  ? trace_hardirqs_on (kernel/trace/trace_preemptirq.c:79 (discriminator 1))
[   98.406499]  ? srso_alias_return_thunk (arch/x86/lib/retpoline.S:221)
[   98.406523]  ? kthread (kernel/kthread.c:433)
[   98.406539]  ? srso_alias_return_thunk (arch/x86/lib/retpoline.S:221)
[   98.406565]  ? kthread (kernel/kthread.c:433)
[   98.406581]  ? __pfx_hidp_session_thread (net/bluetooth/hidp/core.c:1264)
[   98.406610]  kthread (kernel/kthread.c:467)
[   98.406627]  ? __pfx_kthread (kernel/kthread.c:412)
[   98.406645]  ret_from_fork (arch/x86/kernel/process.c:164)
[   98.406674]  ? __pfx_ret_from_fork (arch/x86/kernel/process.c:153)
[   98.406704]  ? srso_alias_return_thunk (arch/x86/lib/retpoline.S:221)
[   98.406728]  ? __pfx_kthread (kernel/kthread.c:412)
[   98.406747]  ret_from_fork_asm (arch/x86/entry/entry_64.S:258)
[   98.406774]  </TASK>
[   98.406780]
[   98.433693] The buggy address belongs to the physical page:
[   98.434405] page: refcount:0 mapcount:0 mapping:0000000000000000 index:0xffff888113ee7c40 pfn:0x113ee4
[   98.435557] flags: 0x200000000000000(node=0|zone=2)
[   98.436198] raw: 0200000000000000 ffffea0004244308 ffff8881f6f3ebc0 0000000000000000
[   98.437195] raw: ffff888113ee7c40 0000000000000000 00000000ffffffff 0000000000000000
[   98.438115] page dumped because: kasan: bad access detected
[   98.438951]
[   98.439211] Memory state around the buggy address:
[   98.439871]  ffff888113ee3f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
[   98.440714]  ffff888113ee4000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
[   98.441580] >ffff888113ee4080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
[   98.442458]                                   ^
[   98.443011]  ffff888113ee4100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
[   98.443889]  ffff888113ee4180: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
[   98.444768] ==================================================================
[   98.445719] Disabling lock debugging due to kernel taint
[   98.448074] l2cap_conn_free: freeing conn ffff88810c22b400
[   98.450012] CPU: 1 UID: 0 PID: 1430 Comm: khidpd_00050004 Tainted: G    B               7.0.0-rc1-dirty #14 PREEMPT(lazy)
[   98.450040] Tainted: [B]=BAD_PAGE
[   98.450047] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.17.0-debian-1.17.0-1 04/01/2014
[   98.450059] Call Trace:
[   98.450065]  <TASK>
[   98.450071]  dump_stack_lvl (lib/dump_stack.c:122)
[   98.450099]  l2cap_conn_free (net/bluetooth/l2cap_core.c:1808)
[   98.450125]  l2cap_conn_put (net/bluetooth/l2cap_core.c:1822)
[   98.450154]  session_free (net/bluetooth/hidp/core.c:990)
[   98.450181]  hidp_session_thread (net/bluetooth/hidp/core.c:1307)
[   98.450213]  ? __pfx_hidp_session_thread (net/bluetooth/hidp/core.c:1264)
[   98.450271]  ? kthread (kernel/kthread.c:433)
[   98.450293]  ? __pfx_hidp_session_wake_function (net/bluetooth/hidp/core.c:1251)
[   98.450339]  ? srso_alias_return_thunk (arch/x86/lib/retpoline.S:221)
[   98.450368]  ? find_held_lock (kernel/locking/lockdep.c:5350 (discriminator 1))
[   98.450406]  ? __pfx_hidp_session_wake_function (net/bluetooth/hidp/core.c:1251)
[   98.450442]  ? srso_alias_return_thunk (arch/x86/lib/retpoline.S:221)
[   98.450471]  ? trace_hardirqs_on (kernel/trace/trace_preemptirq.c:79 (discriminator 1))
[   98.450499]  ? srso_alias_return_thunk (arch/x86/lib/retpoline.S:221)
[   98.450528]  ? kthread (kernel/kthread.c:433)
[   98.450547]  ? srso_alias_return_thunk (arch/x86/lib/retpoline.S:221)
[   98.450578]  ? kthread (kernel/kthread.c:433)
[   98.450598]  ? __pfx_hidp_session_thread (net/bluetooth/hidp/core.c:1264)
[   98.450637]  kthread (kernel/kthread.c:467)
[   98.450657]  ? __pfx_kthread (kernel/kthread.c:412)
[   98.450680]  ret_from_fork (arch/x86/kernel/process.c:164)
[   98.450715]  ? __pfx_ret_from_fork (arch/x86/kernel/process.c:153)
[   98.450752]  ? srso_alias_return_thunk (arch/x86/lib/retpoline.S:221)
[   98.450782]  ? __pfx_kthread (kernel/kthread.c:412)
[   98.450804]  ret_from_fork_asm (arch/x86/entry/entry_64.S:258)
[   98.450836]  </TASK>

Fixes: b4f34d8d9d26 ("Bluetooth: hidp: add new session-management helpers")
Reported-by: soufiane el hachmi <kilwa10@gmail.com>
Tested-by: soufiane el hachmi <kilwa10@gmail.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
---
 net/bluetooth/hidp/core.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/net/bluetooth/hidp/core.c b/net/bluetooth/hidp/core.c
index 6fe815241b01..7bcf8c5ceaee 100644
--- a/net/bluetooth/hidp/core.c
+++ b/net/bluetooth/hidp/core.c
@@ -986,7 +986,8 @@ static void session_free(struct kref *ref)
 	skb_queue_purge(&session->intr_transmit);
 	fput(session->intr_sock->file);
 	fput(session->ctrl_sock->file);
-	l2cap_conn_put(session->conn);
+	if (session->conn)
+		l2cap_conn_put(session->conn);
 	kfree(session);
 }
 
@@ -1164,6 +1165,15 @@ static void hidp_session_remove(struct l2cap_conn *conn,
 
 	down_write(&hidp_session_sem);
 
+	/* Drop L2CAP reference immediately to indicate that
+	 * l2cap_unregister_user() shall not be called as it is already
+	 * considered removed.
+	 */
+	if (session->conn) {
+		l2cap_conn_put(session->conn);
+		session->conn = NULL;
+	}
+
 	hidp_session_terminate(session);
 
 	cancel_work_sync(&session->dev_init);
@@ -1301,7 +1311,9 @@ static int hidp_session_thread(void *arg)
 	 * Instead, this call has the same semantics as if user-space tried to
 	 * delete the session.
 	 */
-	l2cap_unregister_user(session->conn, &session->user);
+	if (session->conn)
+		l2cap_unregister_user(session->conn, &session->user);
+
 	hidp_session_put(session);
 
 	module_put_and_kthread_exit(0);
-- 
2.53.0


^ permalink raw reply related	[flat|nested] 23+ messages in thread
* Re: [RESEND] Bluetooth: L2CAP: Fix use-after-free in l2cap_unregister_user
  2026-03-07  8:59 [RESEND] Bluetooth: L2CAP: Fix use-after-free " Pauli Virtanen
@ 2026-03-07  9:45 Pauli Virtanen
  2026-03-07 10:22 ` [syzbot] [bluetooth?] KASAN: slab-use-after-free Read " syzbot
  0 siblings, 1 reply; 23+ messages in thread
From: Pauli Virtanen @ 2026-03-07  9:45 UTC (permalink / raw)
  To: linux-bluetooth; +Cc: syzbot+14b6d57fb728e27ce23c

[-- Attachment #1: Type: text/plain, Size: 4052 bytes --]

la, 2026-03-07 kello 10:59 +0200, Pauli Virtanen kirjoitti:
> pe, 2026-03-06 kello 16:04 -0500, Luiz Augusto von Dentz kirjoitti:
> > From: Shaurya Rane <ssrane_b23@ee.vjti.ac.in>
> > 
> > After commit ab4eedb790ca ("Bluetooth: L2CAP: Fix corrupted list in
> > hci_chan_del"), l2cap_conn_del() uses conn->lock to protect access to
> > conn->users and conn->hchan. However, l2cap_register_user() and
> > l2cap_unregister_user() still use hci_dev_lock(), creating a race
> > condition where these functions can access conn->users and conn->hchan
> > concurrently with l2cap_conn_del().
> 
> AFAIK the above text from the original submitter is a bit inaccurate,
> as l2cap_conn_del() is called with hdev lock held, so conn->users/hchan
> should be safe.
> 
> However, using conn->mutex should fix the use-after-free in
> 
> 	conn->hcon->hdev
> 	hci_dev_lock(hdev);
> 	hci_dev_unlock(hdev);
> 
> by making l2cap_unregister_user() safe to call after the hcon/hdev are
> no longer alive.
> 
> The change looks OK to me, but probably worth to double check with
> syzbot it fixes the original issue

syzbot seems to have hit some internal error, another try on upstream
branch instead

#syz test

> > This can lead to use-after-free and list corruption bugs, as reported
> > by syzbot.
> > 
> > Fix this by changing l2cap_register_user() and l2cap_unregister_user()
> > to use conn->lock instead of hci_dev_lock(), ensuring consistent locking
> > for the l2cap_conn structure.
> > Reported-by: syzbot+14b6d57fb728e27ce23c@syzkaller.appspotmail.com
> > Closes: https://syzkaller.appspot.com/bug?extid=14b6d57fb728e27ce23c
> > Fixes: ab4eedb790ca ("Bluetooth: L2CAP: Fix corrupted list in hci_chan_del")
> > Signed-off-by: Shaurya Rane <ssrane_b23@ee.vjti.ac.in>
> > Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
> > ---
> >  net/bluetooth/l2cap_core.c | 20 ++++++++------------
> >  1 file changed, 8 insertions(+), 12 deletions(-)
> > 
> > diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
> > index 14131e427efd..6606d7f12534 100644
> > --- a/net/bluetooth/l2cap_core.c
> > +++ b/net/bluetooth/l2cap_core.c
> > @@ -1678,17 +1678,15 @@ static void l2cap_info_timeout(struct work_struct *work)
> >  
> >  int l2cap_register_user(struct l2cap_conn *conn, struct l2cap_user *user)
> >  {
> > -	struct hci_dev *hdev = conn->hcon->hdev;
> >  	int ret;
> >  
> >  	/* We need to check whether l2cap_conn is registered. If it is not, we
> > -	 * must not register the l2cap_user. l2cap_conn_del() is unregisters
> > -	 * l2cap_conn objects, but doesn't provide its own locking. Instead, it
> > -	 * relies on the parent hci_conn object to be locked. This itself relies
> > -	 * on the hci_dev object to be locked. So we must lock the hci device
> > -	 * here, too. */
> > +	 * must not register the l2cap_user. l2cap_conn_del() unregisters
> > +	 * l2cap_conn objects under conn->lock, and we use the same lock here
> > +	 * to protect access to conn->users and conn->hchan.
> > +	 */
> >  
> > -	hci_dev_lock(hdev);
> > +	mutex_lock(&conn->lock);
> >  
> >  	if (!list_empty(&user->list)) {
> >  		ret = -EINVAL;
> > @@ -1709,16 +1707,14 @@ int l2cap_register_user(struct l2cap_conn *conn, struct l2cap_user *user)
> >  	ret = 0;
> >  
> >  out_unlock:
> > -	hci_dev_unlock(hdev);
> > +	mutex_unlock(&conn->lock);
> >  	return ret;
> >  }
> >  EXPORT_SYMBOL(l2cap_register_user);
> >  
> >  void l2cap_unregister_user(struct l2cap_conn *conn, struct l2cap_user *user)
> >  {
> > -	struct hci_dev *hdev = conn->hcon->hdev;
> > -
> > -	hci_dev_lock(hdev);
> > +	mutex_lock(&conn->lock);
> >  
> >  	if (list_empty(&user->list))
> >  		goto out_unlock;
> > @@ -1727,7 +1723,7 @@ void l2cap_unregister_user(struct l2cap_conn *conn, struct l2cap_user *user)
> >  	user->remove(conn, user);
> >  
> >  out_unlock:
> > -	hci_dev_unlock(hdev);
> > +	mutex_unlock(&conn->lock);
> >  }
> >  EXPORT_SYMBOL(l2cap_unregister_user);
> >  

[-- Attachment #2: 0001-Bluetooth-L2CAP-Fix-use-after-free-in-l2cap_unregist.patch --]
[-- Type: text/x-patch, Size: 3220 bytes --]

From 2d0e9ce3888e494c12324c0f682900d9f61d5eb2 Mon Sep 17 00:00:00 2001
Message-ID: <2d0e9ce3888e494c12324c0f682900d9f61d5eb2.1772873329.git.pav@iki.fi>
From: Shaurya Rane <ssrane_b23@ee.vjti.ac.in>
Date: Fri, 6 Mar 2026 16:04:27 -0500
Subject: [PATCH] Bluetooth: L2CAP: Fix use-after-free in l2cap_unregister_user
To: linux-bluetooth@vger.kernel.org

After commit ab4eedb790ca ("Bluetooth: L2CAP: Fix corrupted list in
hci_chan_del"), l2cap_conn_del() uses conn->lock to protect access to
conn->users and conn->hchan. However, l2cap_register_user() and
l2cap_unregister_user() still use hci_dev_lock(), creating a race
condition where these functions can access conn->users and conn->hchan
concurrently with l2cap_conn_del().

This can lead to use-after-free and list corruption bugs, as reported
by syzbot.

Fix this by changing l2cap_register_user() and l2cap_unregister_user()
to use conn->lock instead of hci_dev_lock(), ensuring consistent locking
for the l2cap_conn structure.

Reported-by: syzbot+14b6d57fb728e27ce23c@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=14b6d57fb728e27ce23c
Fixes: ab4eedb790ca ("Bluetooth: L2CAP: Fix corrupted list in hci_chan_del")
Signed-off-by: Shaurya Rane <ssrane_b23@ee.vjti.ac.in>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
---
 net/bluetooth/l2cap_core.c | 20 ++++++++------------
 1 file changed, 8 insertions(+), 12 deletions(-)

diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
index 14131e427efd..6606d7f12534 100644
--- a/net/bluetooth/l2cap_core.c
+++ b/net/bluetooth/l2cap_core.c
@@ -1678,17 +1678,15 @@ static void l2cap_info_timeout(struct work_struct *work)
 
 int l2cap_register_user(struct l2cap_conn *conn, struct l2cap_user *user)
 {
-	struct hci_dev *hdev = conn->hcon->hdev;
 	int ret;
 
 	/* We need to check whether l2cap_conn is registered. If it is not, we
-	 * must not register the l2cap_user. l2cap_conn_del() is unregisters
-	 * l2cap_conn objects, but doesn't provide its own locking. Instead, it
-	 * relies on the parent hci_conn object to be locked. This itself relies
-	 * on the hci_dev object to be locked. So we must lock the hci device
-	 * here, too. */
+	 * must not register the l2cap_user. l2cap_conn_del() unregisters
+	 * l2cap_conn objects under conn->lock, and we use the same lock here
+	 * to protect access to conn->users and conn->hchan.
+	 */
 
-	hci_dev_lock(hdev);
+	mutex_lock(&conn->lock);
 
 	if (!list_empty(&user->list)) {
 		ret = -EINVAL;
@@ -1709,16 +1707,14 @@ int l2cap_register_user(struct l2cap_conn *conn, struct l2cap_user *user)
 	ret = 0;
 
 out_unlock:
-	hci_dev_unlock(hdev);
+	mutex_unlock(&conn->lock);
 	return ret;
 }
 EXPORT_SYMBOL(l2cap_register_user);
 
 void l2cap_unregister_user(struct l2cap_conn *conn, struct l2cap_user *user)
 {
-	struct hci_dev *hdev = conn->hcon->hdev;
-
-	hci_dev_lock(hdev);
+	mutex_lock(&conn->lock);
 
 	if (list_empty(&user->list))
 		goto out_unlock;
@@ -1727,7 +1723,7 @@ void l2cap_unregister_user(struct l2cap_conn *conn, struct l2cap_user *user)
 	user->remove(conn, user);
 
 out_unlock:
-	hci_dev_unlock(hdev);
+	mutex_unlock(&conn->lock);
 }
 EXPORT_SYMBOL(l2cap_unregister_user);
 
-- 
2.53.0


^ permalink raw reply related	[flat|nested] 23+ messages in thread
* Re: [RESEND] Bluetooth: L2CAP: Fix use-after-free in l2cap_unregister_user
@ 2026-03-07  8:59 Pauli Virtanen
  2026-03-07  9:33 ` [syzbot] [bluetooth?] KASAN: slab-use-after-free Read " syzbot
  0 siblings, 1 reply; 23+ messages in thread
From: Pauli Virtanen @ 2026-03-07  8:59 UTC (permalink / raw)
  To: linux-bluetooth; +Cc: syzbot+14b6d57fb728e27ce23c

[-- Attachment #1: Type: text/plain, Size: 3794 bytes --]

pe, 2026-03-06 kello 16:04 -0500, Luiz Augusto von Dentz kirjoitti:
> From: Shaurya Rane <ssrane_b23@ee.vjti.ac.in>
> 
> After commit ab4eedb790ca ("Bluetooth: L2CAP: Fix corrupted list in
> hci_chan_del"), l2cap_conn_del() uses conn->lock to protect access to
> conn->users and conn->hchan. However, l2cap_register_user() and
> l2cap_unregister_user() still use hci_dev_lock(), creating a race
> condition where these functions can access conn->users and conn->hchan
> concurrently with l2cap_conn_del().

AFAIK the above text from the original submitter is a bit inaccurate,
as l2cap_conn_del() is called with hdev lock held, so conn->users/hchan
should be safe.

However, using conn->mutex should fix the use-after-free in

	conn->hcon->hdev
	hci_dev_lock(hdev);
	hci_dev_unlock(hdev);

by making l2cap_unregister_user() safe to call after the hcon/hdev are
no longer alive.

The change looks OK to me, but probably worth to double check with
syzbot it fixes the original issue

#syz test git://git.kernel.org/pub/scm/linux/kernel/git/bluetooth/bluetooth-next.git master

> This can lead to use-after-free and list corruption bugs, as reported
> by syzbot.
> 
> Fix this by changing l2cap_register_user() and l2cap_unregister_user()
> to use conn->lock instead of hci_dev_lock(), ensuring consistent locking
> for the l2cap_conn structure.
> Reported-by: syzbot+14b6d57fb728e27ce23c@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=14b6d57fb728e27ce23c
> Fixes: ab4eedb790ca ("Bluetooth: L2CAP: Fix corrupted list in hci_chan_del")
> Signed-off-by: Shaurya Rane <ssrane_b23@ee.vjti.ac.in>
> Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
> ---
>  net/bluetooth/l2cap_core.c | 20 ++++++++------------
>  1 file changed, 8 insertions(+), 12 deletions(-)
> 
> diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
> index 14131e427efd..6606d7f12534 100644
> --- a/net/bluetooth/l2cap_core.c
> +++ b/net/bluetooth/l2cap_core.c
> @@ -1678,17 +1678,15 @@ static void l2cap_info_timeout(struct work_struct *work)
>  
>  int l2cap_register_user(struct l2cap_conn *conn, struct l2cap_user *user)
>  {
> -	struct hci_dev *hdev = conn->hcon->hdev;
>  	int ret;
>  
>  	/* We need to check whether l2cap_conn is registered. If it is not, we
> -	 * must not register the l2cap_user. l2cap_conn_del() is unregisters
> -	 * l2cap_conn objects, but doesn't provide its own locking. Instead, it
> -	 * relies on the parent hci_conn object to be locked. This itself relies
> -	 * on the hci_dev object to be locked. So we must lock the hci device
> -	 * here, too. */
> +	 * must not register the l2cap_user. l2cap_conn_del() unregisters
> +	 * l2cap_conn objects under conn->lock, and we use the same lock here
> +	 * to protect access to conn->users and conn->hchan.
> +	 */
>  
> -	hci_dev_lock(hdev);
> +	mutex_lock(&conn->lock);
>  
>  	if (!list_empty(&user->list)) {
>  		ret = -EINVAL;
> @@ -1709,16 +1707,14 @@ int l2cap_register_user(struct l2cap_conn *conn, struct l2cap_user *user)
>  	ret = 0;
>  
>  out_unlock:
> -	hci_dev_unlock(hdev);
> +	mutex_unlock(&conn->lock);
>  	return ret;
>  }
>  EXPORT_SYMBOL(l2cap_register_user);
>  
>  void l2cap_unregister_user(struct l2cap_conn *conn, struct l2cap_user *user)
>  {
> -	struct hci_dev *hdev = conn->hcon->hdev;
> -
> -	hci_dev_lock(hdev);
> +	mutex_lock(&conn->lock);
>  
>  	if (list_empty(&user->list))
>  		goto out_unlock;
> @@ -1727,7 +1723,7 @@ void l2cap_unregister_user(struct l2cap_conn *conn, struct l2cap_user *user)
>  	user->remove(conn, user);
>  
>  out_unlock:
> -	hci_dev_unlock(hdev);
> +	mutex_unlock(&conn->lock);
>  }
>  EXPORT_SYMBOL(l2cap_unregister_user);
>  

[-- Attachment #2: 0001-Bluetooth-L2CAP-Fix-use-after-free-in-l2cap_unregist.patch --]
[-- Type: text/x-patch, Size: 3220 bytes --]

From 2d0e9ce3888e494c12324c0f682900d9f61d5eb2 Mon Sep 17 00:00:00 2001
Message-ID: <2d0e9ce3888e494c12324c0f682900d9f61d5eb2.1772873329.git.pav@iki.fi>
From: Shaurya Rane <ssrane_b23@ee.vjti.ac.in>
Date: Fri, 6 Mar 2026 16:04:27 -0500
Subject: [PATCH] Bluetooth: L2CAP: Fix use-after-free in l2cap_unregister_user
To: linux-bluetooth@vger.kernel.org

After commit ab4eedb790ca ("Bluetooth: L2CAP: Fix corrupted list in
hci_chan_del"), l2cap_conn_del() uses conn->lock to protect access to
conn->users and conn->hchan. However, l2cap_register_user() and
l2cap_unregister_user() still use hci_dev_lock(), creating a race
condition where these functions can access conn->users and conn->hchan
concurrently with l2cap_conn_del().

This can lead to use-after-free and list corruption bugs, as reported
by syzbot.

Fix this by changing l2cap_register_user() and l2cap_unregister_user()
to use conn->lock instead of hci_dev_lock(), ensuring consistent locking
for the l2cap_conn structure.

Reported-by: syzbot+14b6d57fb728e27ce23c@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=14b6d57fb728e27ce23c
Fixes: ab4eedb790ca ("Bluetooth: L2CAP: Fix corrupted list in hci_chan_del")
Signed-off-by: Shaurya Rane <ssrane_b23@ee.vjti.ac.in>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
---
 net/bluetooth/l2cap_core.c | 20 ++++++++------------
 1 file changed, 8 insertions(+), 12 deletions(-)

diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
index 14131e427efd..6606d7f12534 100644
--- a/net/bluetooth/l2cap_core.c
+++ b/net/bluetooth/l2cap_core.c
@@ -1678,17 +1678,15 @@ static void l2cap_info_timeout(struct work_struct *work)
 
 int l2cap_register_user(struct l2cap_conn *conn, struct l2cap_user *user)
 {
-	struct hci_dev *hdev = conn->hcon->hdev;
 	int ret;
 
 	/* We need to check whether l2cap_conn is registered. If it is not, we
-	 * must not register the l2cap_user. l2cap_conn_del() is unregisters
-	 * l2cap_conn objects, but doesn't provide its own locking. Instead, it
-	 * relies on the parent hci_conn object to be locked. This itself relies
-	 * on the hci_dev object to be locked. So we must lock the hci device
-	 * here, too. */
+	 * must not register the l2cap_user. l2cap_conn_del() unregisters
+	 * l2cap_conn objects under conn->lock, and we use the same lock here
+	 * to protect access to conn->users and conn->hchan.
+	 */
 
-	hci_dev_lock(hdev);
+	mutex_lock(&conn->lock);
 
 	if (!list_empty(&user->list)) {
 		ret = -EINVAL;
@@ -1709,16 +1707,14 @@ int l2cap_register_user(struct l2cap_conn *conn, struct l2cap_user *user)
 	ret = 0;
 
 out_unlock:
-	hci_dev_unlock(hdev);
+	mutex_unlock(&conn->lock);
 	return ret;
 }
 EXPORT_SYMBOL(l2cap_register_user);
 
 void l2cap_unregister_user(struct l2cap_conn *conn, struct l2cap_user *user)
 {
-	struct hci_dev *hdev = conn->hcon->hdev;
-
-	hci_dev_lock(hdev);
+	mutex_lock(&conn->lock);
 
 	if (list_empty(&user->list))
 		goto out_unlock;
@@ -1727,7 +1723,7 @@ void l2cap_unregister_user(struct l2cap_conn *conn, struct l2cap_user *user)
 	user->remove(conn, user);
 
 out_unlock:
-	hci_dev_unlock(hdev);
+	mutex_unlock(&conn->lock);
 }
 EXPORT_SYMBOL(l2cap_unregister_user);
 
-- 
2.53.0


^ permalink raw reply related	[flat|nested] 23+ messages in thread
* [syzbot] [bluetooth?] KASAN: slab-use-after-free Read in l2cap_unregister_user
@ 2024-11-01 18:29 syzbot
  2024-11-02  1:27 ` Hillf Danton
                   ` (2 more replies)
  0 siblings, 3 replies; 23+ messages in thread
From: syzbot @ 2024-11-01 18:29 UTC (permalink / raw)
  To: johan.hedberg, linux-bluetooth, linux-kernel, luiz.dentz, marcel,
	syzkaller-bugs

Hello,

syzbot found the following issue on:

HEAD commit:    90602c251cda Merge tag 'net-6.12-rc6' of git://git.kernel...
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=10076630580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=4340261e4e9f37fc
dashboard link: https://syzkaller.appspot.com/bug?extid=14b6d57fb728e27ce23c
compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=15bd9340580000

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/7feb34a89c2a/non_bootable_disk-90602c25.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/6a2daa3dcb25/vmlinux-90602c25.xz
kernel image: https://storage.googleapis.com/syzbot-assets/4488ee6eec29/bzImage-90602c25.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+14b6d57fb728e27ce23c@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: slab-use-after-free in __mutex_waiter_is_first kernel/locking/mutex.c:197 [inline]
BUG: KASAN: slab-use-after-free in __mutex_lock_common kernel/locking/mutex.c:686 [inline]
BUG: KASAN: slab-use-after-free in __mutex_lock+0x8e6/0x9c0 kernel/locking/mutex.c:752
Read of size 8 at addr ffff888021760060 by task khidpd_0007fff9/6116

CPU: 3 UID: 0 PID: 6116 Comm: khidpd_0007fff9 Not tainted 6.12.0-rc5-syzkaller-00161-g90602c251cda #0
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:377 [inline]
 print_report+0xc3/0x620 mm/kasan/report.c:488
 kasan_report+0xd9/0x110 mm/kasan/report.c:601
 __mutex_waiter_is_first kernel/locking/mutex.c:197 [inline]
 __mutex_lock_common kernel/locking/mutex.c:686 [inline]
 __mutex_lock+0x8e6/0x9c0 kernel/locking/mutex.c:752
 l2cap_unregister_user+0x71/0x240 net/bluetooth/l2cap_core.c:1726
 hidp_session_thread+0x462/0x650 net/bluetooth/hidp/core.c:1304
 kthread+0x2c1/0x3a0 kernel/kthread.c:389
 ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
 </TASK>

Allocated by task 6062:
 kasan_save_stack+0x33/0x60 mm/kasan/common.c:47
 kasan_save_track+0x14/0x30 mm/kasan/common.c:68
 poison_kmalloc_redzone mm/kasan/common.c:377 [inline]
 __kasan_kmalloc+0xaa/0xb0 mm/kasan/common.c:394
 kasan_kmalloc include/linux/kasan.h:257 [inline]
 __do_kmalloc_node mm/slub.c:4264 [inline]
 __kmalloc_noprof+0x1e8/0x400 mm/slub.c:4276
 kmalloc_noprof include/linux/slab.h:882 [inline]
 kzalloc_noprof include/linux/slab.h:1014 [inline]
 hci_alloc_dev_priv+0x1d/0x2820 net/bluetooth/hci_core.c:2440
 hci_alloc_dev include/net/bluetooth/hci_core.h:1621 [inline]
 __vhci_create_device+0xef/0x7d0 drivers/bluetooth/hci_vhci.c:399
 vhci_create_device drivers/bluetooth/hci_vhci.c:470 [inline]
 vhci_get_user drivers/bluetooth/hci_vhci.c:527 [inline]
 vhci_write+0x2c3/0x470 drivers/bluetooth/hci_vhci.c:607
 new_sync_write fs/read_write.c:590 [inline]
 vfs_write+0x5ae/0x1150 fs/read_write.c:683
 ksys_write+0x12f/0x260 fs/read_write.c:736
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 6062:
 kasan_save_stack+0x33/0x60 mm/kasan/common.c:47
 kasan_save_track+0x14/0x30 mm/kasan/common.c:68
 kasan_save_free_info+0x3b/0x60 mm/kasan/generic.c:579
 poison_slab_object mm/kasan/common.c:247 [inline]
 __kasan_slab_free+0x51/0x70 mm/kasan/common.c:264
 kasan_slab_free include/linux/kasan.h:230 [inline]
 slab_free_hook mm/slub.c:2342 [inline]
 slab_free mm/slub.c:4579 [inline]
 kfree+0x14f/0x4b0 mm/slub.c:4727
 hci_release_dev+0x4d9/0x600 net/bluetooth/hci_core.c:2759
 bt_host_release+0x6a/0xb0 net/bluetooth/hci_sysfs.c:94
 device_release+0xa1/0x240 drivers/base/core.c:2575
 kobject_cleanup lib/kobject.c:689 [inline]
 kobject_release lib/kobject.c:720 [inline]
 kref_put include/linux/kref.h:65 [inline]
 kobject_put+0x1e4/0x5a0 lib/kobject.c:737
 put_device+0x1f/0x30 drivers/base/core.c:3783
 vhci_release+0x81/0xf0 drivers/bluetooth/hci_vhci.c:665
 __fput+0x3f6/0xb60 fs/file_table.c:431
 task_work_run+0x14e/0x250 kernel/task_work.c:239
 exit_task_work include/linux/task_work.h:43 [inline]
 do_exit+0xadd/0x2d70 kernel/exit.c:939
 do_group_exit+0xd3/0x2a0 kernel/exit.c:1088
 __do_sys_exit_group kernel/exit.c:1099 [inline]
 __se_sys_exit_group kernel/exit.c:1097 [inline]
 __x64_sys_exit_group+0x3e/0x50 kernel/exit.c:1097
 x64_sys_call+0x14a9/0x16a0 arch/x86/include/generated/asm/syscalls_64.h:232
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Last potentially related work creation:
 kasan_save_stack+0x33/0x60 mm/kasan/common.c:47
 __kasan_record_aux_stack+0xba/0xd0 mm/kasan/generic.c:541
 insert_work+0x36/0x230 kernel/workqueue.c:2183
 __queue_work+0x3f8/0x1080 kernel/workqueue.c:2343
 queue_work_on+0x11a/0x140 kernel/workqueue.c:2390
 process_one_work+0x9c5/0x1ba0 kernel/workqueue.c:3229
 process_scheduled_works kernel/workqueue.c:3310 [inline]
 worker_thread+0x6c8/0xf00 kernel/workqueue.c:3391
 kthread+0x2c1/0x3a0 kernel/kthread.c:389
 ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244

Second to last potentially related work creation:
 kasan_save_stack+0x33/0x60 mm/kasan/common.c:47
 __kasan_record_aux_stack+0xba/0xd0 mm/kasan/generic.c:541
 insert_work+0x36/0x230 kernel/workqueue.c:2183
 __queue_work+0x97e/0x1080 kernel/workqueue.c:2339
 call_timer_fn+0x1a0/0x610 kernel/time/timer.c:1794
 expire_timers kernel/time/timer.c:1840 [inline]
 __run_timers+0x56a/0x930 kernel/time/timer.c:2419
 __run_timer_base kernel/time/timer.c:2430 [inline]
 __run_timer_base kernel/time/timer.c:2423 [inline]
 run_timer_base+0x111/0x190 kernel/time/timer.c:2439
 run_timer_softirq+0x1a/0x40 kernel/time/timer.c:2449
 handle_softirqs+0x213/0x8f0 kernel/softirq.c:554
 __do_softirq kernel/softirq.c:588 [inline]
 invoke_softirq kernel/softirq.c:428 [inline]
 __irq_exit_rcu kernel/softirq.c:637 [inline]
 irq_exit_rcu+0xbb/0x120 kernel/softirq.c:649
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1049 [inline]
 sysvec_apic_timer_interrupt+0xa4/0xc0 arch/x86/kernel/apic/apic.c:1049
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:702

The buggy address belongs to the object at ffff888021760000
 which belongs to the cache kmalloc-8k of size 8192
The buggy address is located 96 bytes inside of
 freed 8192-byte region [ffff888021760000, ffff888021762000)

The buggy address belongs to the physical page:
page: refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x21760
head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
flags: 0xfff00000000040(head|node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000040 ffff88801b043180 dead000000000100 dead000000000122
raw: 0000000000000000 0000000000020002 00000001f5000000 0000000000000000
head: 00fff00000000040 ffff88801b043180 dead000000000100 dead000000000122
head: 0000000000000000 0000000000020002 00000001f5000000 0000000000000000
head: 00fff00000000003 ffffea000085d801 ffffffffffffffff 0000000000000000
head: 0000000000000008 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 3, migratetype Unmovable, gfp_mask 0xd2040(__GFP_IO|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 5654, tgid 5654 (sh), ts 21301582122, free_ts 21285906849
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x2d1/0x350 mm/page_alloc.c:1537
 prep_new_page mm/page_alloc.c:1545 [inline]
 get_page_from_freelist+0x101e/0x3070 mm/page_alloc.c:3457
 __alloc_pages_noprof+0x223/0x25a0 mm/page_alloc.c:4733
 alloc_pages_mpol_noprof+0x2c9/0x610 mm/mempolicy.c:2265
 alloc_slab_page mm/slub.c:2412 [inline]
 allocate_slab mm/slub.c:2578 [inline]
 new_slab+0x2ba/0x3f0 mm/slub.c:2631
 ___slab_alloc+0xdac/0x1880 mm/slub.c:3818
 __slab_alloc.constprop.0+0x56/0xb0 mm/slub.c:3908
 __slab_alloc_node mm/slub.c:3961 [inline]
 slab_alloc_node mm/slub.c:4122 [inline]
 __kmalloc_cache_noprof+0x2b4/0x300 mm/slub.c:4290
 kmalloc_noprof include/linux/slab.h:878 [inline]
 kzalloc_noprof include/linux/slab.h:1014 [inline]
 tomoyo_print_bprm security/tomoyo/audit.c:26 [inline]
 tomoyo_init_log+0xcb3/0x2170 security/tomoyo/audit.c:264
 tomoyo_supervisor+0x30c/0xea0 security/tomoyo/common.c:2089
 tomoyo_audit_path_log security/tomoyo/file.c:168 [inline]
 tomoyo_execute_permission+0x38e/0x4b0 security/tomoyo/file.c:619
 tomoyo_find_next_domain+0x361/0x2070 security/tomoyo/domain.c:755
 tomoyo_bprm_check_security security/tomoyo/tomoyo.c:102 [inline]
 tomoyo_bprm_check_security+0x12b/0x1d0 security/tomoyo/tomoyo.c:92
 security_bprm_check+0x1b9/0x1e0 security/security.c:1297
 search_binary_handler fs/exec.c:1740 [inline]
 exec_binprm fs/exec.c:1794 [inline]
 bprm_execve fs/exec.c:1845 [inline]
 bprm_execve+0x642/0x1960 fs/exec.c:1821
 do_execveat_common.isra.0+0x4f1/0x630 fs/exec.c:1952
page last free pid 5653 tgid 5653 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 free_pages_prepare mm/page_alloc.c:1108 [inline]
 free_unref_page+0x5f4/0xdc0 mm/page_alloc.c:2638
 __put_partials+0x14c/0x170 mm/slub.c:3145
 qlink_free mm/kasan/quarantine.c:163 [inline]
 qlist_free_all+0x4e/0x120 mm/kasan/quarantine.c:179
 kasan_quarantine_reduce+0x192/0x1e0 mm/kasan/quarantine.c:286
 __kasan_slab_alloc+0x69/0x90 mm/kasan/common.c:329
 kasan_slab_alloc include/linux/kasan.h:247 [inline]
 slab_post_alloc_hook mm/slub.c:4085 [inline]
 slab_alloc_node mm/slub.c:4134 [inline]
 __kmalloc_cache_noprof+0x11e/0x300 mm/slub.c:4290
 kmalloc_noprof include/linux/slab.h:878 [inline]
 tomoyo_print_header security/tomoyo/audit.c:156 [inline]
 tomoyo_init_log+0x195/0x2170 security/tomoyo/audit.c:255
 tomoyo_supervisor+0x30c/0xea0 security/tomoyo/common.c:2089
 tomoyo_audit_path_log security/tomoyo/file.c:168 [inline]
 tomoyo_path_permission security/tomoyo/file.c:587 [inline]
 tomoyo_path_permission+0x270/0x3b0 security/tomoyo/file.c:573
 tomoyo_path_perm+0x35e/0x450 security/tomoyo/file.c:838
 security_inode_getattr+0x116/0x290 security/security.c:2373
 vfs_getattr+0x36/0xb0 fs/stat.c:204
 vfs_statx_path+0x36/0x390 fs/stat.c:251
 vfs_statx+0x145/0x1e0 fs/stat.c:315
 vfs_fstatat+0x9f/0x160 fs/stat.c:341
 __do_sys_newfstatat+0xa2/0x130 fs/stat.c:505

Memory state around the buggy address:
 ffff88802175ff00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88802175ff80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff888021760000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                                       ^
 ffff888021760080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888021760100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup

^ permalink raw reply	[flat|nested] 23+ messages in thread
end of thread, other threads:[~2026-03-07 11:00 UTC | newest]

Thread overview: 23+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2025-11-05 14:22 [PATCH] Bluetooth: L2CAP: Fix use-after-free in l2cap_unregister_user ssrane_b23
2025-11-05 14:40 ` shaurya
2025-11-05 15:32   ` [syzbot] [bluetooth?] KASAN: slab-use-after-free Read " syzbot
2025-11-05 19:03     ` shaurya
2025-11-05 19:04       ` syzbot
2025-11-05 19:05     ` shaurya
2025-11-05 19:05       ` syzbot
2025-11-05 19:26   ` [PATCH] Bluetooth: L2CAP: Fix use-after-free " shaurya
2025-11-05 20:14     ` [syzbot] [bluetooth?] KASAN: slab-use-after-free Read " syzbot
2025-11-05 15:05 ` Bluetooth: L2CAP: Fix use-after-free " bluez.test.bot
2025-11-05 19:36 ` [PATCH] " Pauli Virtanen
2025-11-06 18:20 ` [PATCH v2 1/1] " ssrane_b23
2025-11-06 18:43   ` [v2,1/1] " bluez.test.bot
  -- strict thread matches above, loose matches on Subject: below --
2026-03-07 10:32 [RESEND] " Pauli Virtanen
2026-03-07 11:00 ` [syzbot] [bluetooth?] KASAN: slab-use-after-free Read " syzbot
2026-03-07  9:45 [RESEND] Bluetooth: L2CAP: Fix use-after-free " Pauli Virtanen
2026-03-07 10:22 ` [syzbot] [bluetooth?] KASAN: slab-use-after-free Read " syzbot
2026-03-07  8:59 [RESEND] Bluetooth: L2CAP: Fix use-after-free " Pauli Virtanen
2026-03-07  9:33 ` [syzbot] [bluetooth?] KASAN: slab-use-after-free Read " syzbot
2024-11-01 18:29 syzbot
2024-11-02  1:27 ` Hillf Danton
2024-11-02  1:46   ` syzbot
2024-12-23 22:29 ` syzbot
2025-08-12 16:31 ` syzbot
2025-08-13  1:46   ` Hillf Danton
2025-08-13  2:41     ` syzbot

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