[syzbot] [bluetooth?] KASAN: slab-use-after-free Read in l2cap_disconn_ind (3)

[syzbot] [bluetooth?] KASAN: slab-use-after-free Read in l2cap_disconn_ind (3)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    1bfaee9d3351 Merge tag 'fsverity-for-linus' of git://git.k..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=132d7e96580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=59da38148f3a3d24
dashboard link: https://syzkaller.appspot.com/bug?extid=9c40ad7c6ed7165e46e8
compiler:       gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/b5cda08ac5a6/disk-1bfaee9d.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/aad7c1ec90c4/vmlinux-1bfaee9d.xz
kernel image: https://storage.googleapis.com/syzbot-assets/a51d7d927815/bzImage-1bfaee9d.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+9c40ad7c6ed7165e46e8@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: slab-use-after-free in l2cap_disconn_ind+0xd7/0xf0 net/bluetooth/l2cap_core.c:7430
Read of size 1 at addr ffff88807ee53278 by task kworker/u9:1/4933

CPU: 1 UID: 0 PID: 4933 Comm: kworker/u9:1 Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
Workqueue: hci2 hci_conn_timeout
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0x13d/0x4b0 mm/kasan/report.c:482
 kasan_report+0xdf/0x1d0 mm/kasan/report.c:595
 l2cap_disconn_ind+0xd7/0xf0 net/bluetooth/l2cap_core.c:7430
 hci_proto_disconn_ind include/net/bluetooth/hci_core.h:2115 [inline]
 hci_conn_timeout+0x1dc/0x230 net/bluetooth/hci_conn.c:646
 process_one_work+0xa0e/0x1980 kernel/workqueue.c:3302
 process_scheduled_works kernel/workqueue.c:3385 [inline]
 worker_thread+0x5ef/0xe50 kernel/workqueue.c:3466
 kthread+0x370/0x450 kernel/kthread.c:436
 ret_from_fork+0x72b/0xd50 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>

Allocated by task 16760:
 kasan_save_stack+0x30/0x50 mm/kasan/common.c:57
 kasan_save_track+0x14/0x30 mm/kasan/common.c:78
 poison_kmalloc_redzone mm/kasan/common.c:398 [inline]
 __kasan_kmalloc+0xaa/0xb0 mm/kasan/common.c:415
 kmalloc_noprof include/linux/slab.h:950 [inline]
 kzalloc_noprof include/linux/slab.h:1188 [inline]
 l2cap_conn_add.part.0+0x60/0xb00 net/bluetooth/l2cap_core.c:7001
 l2cap_conn_add include/net/bluetooth/l2cap.h:840 [inline]
 l2cap_chan_connect+0x1435/0x1f90 net/bluetooth/l2cap_core.c:7192
 l2cap_sock_connect+0x37a/0x770 net/bluetooth/l2cap_sock.c:256
 __sys_connect_file+0x141/0x1a0 net/socket.c:2148
 __sys_connect+0x141/0x170 net/socket.c:2167
 __do_sys_connect net/socket.c:2173 [inline]
 __se_sys_connect net/socket.c:2170 [inline]
 __x64_sys_connect+0x72/0xb0 net/socket.c:2170
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x10b/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 16756:
 kasan_save_stack+0x30/0x50 mm/kasan/common.c:57
 kasan_save_track+0x14/0x30 mm/kasan/common.c:78
 kasan_save_free_info+0x3b/0x70 mm/kasan/generic.c:584
 poison_slab_object mm/kasan/common.c:253 [inline]
 __kasan_slab_free+0x5f/0x80 mm/kasan/common.c:285
 kasan_slab_free include/linux/kasan.h:235 [inline]
 slab_free_hook mm/slub.c:2689 [inline]
 slab_free mm/slub.c:6250 [inline]
 kfree+0x223/0x6c0 mm/slub.c:6565
 l2cap_conn_free net/bluetooth/l2cap_core.c:1823 [inline]
 kref_put include/linux/kref.h:65 [inline]
 l2cap_conn_put net/bluetooth/l2cap_core.c:1835 [inline]
 l2cap_conn_del+0x57f/0x710 net/bluetooth/l2cap_core.c:1815
 l2cap_connect_cfm+0x9bb/0xf80 net/bluetooth/l2cap_core.c:7374
 hci_connect_cfm include/net/bluetooth/hci_core.h:2139 [inline]
 hci_conn_failed+0x188/0x360 net/bluetooth/hci_conn.c:1409
 hci_abort_conn_sync+0x7d9/0xb20 net/bluetooth/hci_sync.c:5763
 hci_disconnect_all_sync.constprop.0.isra.0+0x155/0x430 net/bluetooth/hci_sync.c:5786
 hci_suspend_sync+0x8b7/0xa70 net/bluetooth/hci_sync.c:6262
 hci_suspend_dev+0x31d/0x540 net/bluetooth/hci_core.c:2850
 hci_suspend_notifier+0x21e/0x330 net/bluetooth/hci_core.c:2421
 notifier_call_chain+0x99/0x400 kernel/notifier.c:85
 notifier_call_chain_robust kernel/notifier.c:120 [inline]
 blocking_notifier_call_chain_robust kernel/notifier.c:345 [inline]
 blocking_notifier_call_chain_robust+0xc8/0x160 kernel/notifier.c:333
 pm_notifier_call_chain_robust+0x27/0x60 kernel/power/main.c:172
 snapshot_open+0x189/0x2a0 kernel/power/user.c:77
 misc_open+0x26d/0x450 drivers/char/misc.c:163
 chrdev_open+0x234/0x6a0 fs/char_dev.c:411
 do_dentry_open+0x6d8/0x1660 fs/open.c:947
 vfs_open+0x82/0x3f0 fs/open.c:1079
 do_open fs/namei.c:4699 [inline]
 path_openat+0x208c/0x31a0 fs/namei.c:4858
 do_file_open+0x20e/0x430 fs/namei.c:4887
 do_sys_openat2+0x10d/0x1e0 fs/open.c:1364
 do_sys_open fs/open.c:1370 [inline]
 __do_sys_openat fs/open.c:1386 [inline]
 __se_sys_openat fs/open.c:1381 [inline]
 __x64_sys_openat+0x12d/0x210 fs/open.c:1381
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x10b/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff88807ee53000
 which belongs to the cache kmalloc-1k of size 1024
The buggy address is located 632 bytes inside of
 freed 1024-byte region [ffff88807ee53000, ffff88807ee53400)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x7ee50
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 ffff88813fe34dc0 dead000000000100 dead000000000122
raw: 0000000000000000 0000000800100010 00000000f5000000 0000000000000000
head: 00fff00000000040 ffff88813fe34dc0 dead000000000100 dead000000000122
head: 0000000000000000 0000000800100010 00000000f5000000 0000000000000000
head: 00fff00000000003 fffffffffffffe01 00000000ffffffff 00000000ffffffff
head: ffffffffffffffff 0000000000000000 00000000ffffffff 0000000000000008
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 3, migratetype Unmovable, gfp_mask 0xd2820(GFP_ATOMIC|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 1151, tgid 1151 (kworker/u8:8), ts 131280693452, free_ts 131177469088
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x153/0x170 mm/page_alloc.c:1858
 prep_new_page mm/page_alloc.c:1866 [inline]
 get_page_from_freelist+0x11a6/0x33b0 mm/page_alloc.c:3946
 __alloc_frozen_pages_noprof+0x27c/0x2bc0 mm/page_alloc.c:5226
 alloc_slab_page mm/slub.c:3278 [inline]
 allocate_slab mm/slub.c:3467 [inline]
 new_slab+0xa6/0x6c0 mm/slub.c:3525
 refill_objects+0x277/0x420 mm/slub.c:7255
 refill_sheaf mm/slub.c:2816 [inline]
 __pcs_replace_empty_main+0x375/0x650 mm/slub.c:4651
 alloc_from_pcs mm/slub.c:4749 [inline]
 slab_alloc_node mm/slub.c:4883 [inline]
 __do_kmalloc_node mm/slub.c:5294 [inline]
 __kmalloc_noprof+0x688/0x850 mm/slub.c:5307
 kmalloc_noprof include/linux/slab.h:954 [inline]
 kzalloc_noprof include/linux/slab.h:1188 [inline]
 neigh_alloc net/core/neighbour.c:521 [inline]
 ___neigh_create+0x1545/0x2950 net/core/neighbour.c:655
 ip6_finish_output2+0xffa/0x1ce0 net/ipv6/ip6_output.c:128
 __ip6_finish_output+0x357/0xdf0 net/ipv6/ip6_output.c:208
 ip6_finish_output net/ipv6/ip6_output.c:219 [inline]
 NF_HOOK_COND include/linux/netfilter.h:307 [inline]
 ip6_output+0x2aa/0xa60 net/ipv6/ip6_output.c:246
 dst_output include/net/dst.h:470 [inline]
 NF_HOOK include/linux/netfilter.h:318 [inline]
 ndisc_send_skb+0xa85/0x1bf0 net/ipv6/ndisc.c:512
 ndisc_send_rs+0x129/0x680 net/ipv6/ndisc.c:723
 addrconf_rs_timer+0x424/0x880 net/ipv6/addrconf.c:4049
 call_timer_fn+0x19a/0x640 kernel/time/timer.c:1748
 expire_timers kernel/time/timer.c:1799 [inline]
 __run_timers+0x75f/0xaf0 kernel/time/timer.c:2374
page last free pid 5637 tgid 5637 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 __free_pages_prepare mm/page_alloc.c:1402 [inline]
 __free_frozen_pages+0x747/0x1040 mm/page_alloc.c:2943
 qlink_free mm/kasan/quarantine.c:163 [inline]
 qlist_free_all+0x47/0xf0 mm/kasan/quarantine.c:179
 kasan_quarantine_reduce+0x1a0/0x1f0 mm/kasan/quarantine.c:286
 __kasan_slab_alloc+0x69/0x90 mm/kasan/common.c:350
 kasan_slab_alloc include/linux/kasan.h:253 [inline]
 slab_post_alloc_hook mm/slub.c:4569 [inline]
 slab_alloc_node mm/slub.c:4898 [inline]
 kmem_cache_alloc_noprof+0x241/0x6e0 mm/slub.c:4905
 alloc_filename fs/namei.c:142 [inline]
 do_getname+0x35/0x390 fs/namei.c:182
 getname include/linux/fs.h:2526 [inline]
 class_filename_constructor include/linux/fs.h:2553 [inline]
 do_sys_openat2+0xc5/0x1e0 fs/open.c:1363
 do_sys_open fs/open.c:1370 [inline]
 __do_sys_openat fs/open.c:1386 [inline]
 __se_sys_openat fs/open.c:1381 [inline]
 __x64_sys_openat+0x12d/0x210 fs/open.c:1381
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x10b/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:
 ffff88807ee53100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88807ee53180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff88807ee53200: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                                                ^
 ffff88807ee53280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88807ee53300: 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 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

[PATCH] Bluetooth: L2CAP: Fix slab-use-after-free in l2cap_disconn_ind

[Hojun Choi]

l2cap_disconn_ind() runs from the hci_conn_timeout() worker without
hci_dev_lock, and reads conn->disc_reason via hcon->l2cap_data. It races
the teardown path: hci_conn_failed() frees the l2cap_conn via
hci_connect_cfm() -> l2cap_conn_del() and only afterwards drains the
worker via hci_conn_del(), so the worker can read disc_reason after the
l2cap_conn has been freed:

| BUG: KASAN: slab-use-after-free in l2cap_disconn_ind+0xd7/0xf0
| Read of size 1 at addr ffff88807ee53278 by task kworker/u9:1/4933
|  l2cap_disconn_ind net/bluetooth/l2cap_core.c:7430
|  hci_conn_timeout net/bluetooth/hci_conn.c:646

l2cap_conn_del() is always called under hci_dev_lock(), so hold it while
dereferencing hcon->l2cap_data and reading disc_reason. A blocking lock
cannot be used here: hci_conn_del() drains this worker with
disable_delayed_work_sync() while holding hci_dev_lock(), so the worker
would deadlock against the drain. Use a trylock; on contention return the
default HCI_ERROR_REMOTE_USER_TERM, the same reason the !conn path already
returns.

Fixes: 2950f21acb0f ("Bluetooth: Ask upper layers for HCI disconnect reason")
Reported-by: syzbot+9c40ad7c6ed7165e46e8@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=9c40ad7c6ed7165e46e8
Cc: <stable@vger.kernel.org>
Signed-off-by: Hojun Choi <ghwns6743@gmail.com>
---
 include/net/bluetooth/hci_core.h |  1 +
 net/bluetooth/l2cap_core.c       | 24 ++++++++++++++++++++----
 2 files changed, 21 insertions(+), 4 deletions(-)

diff --git a/include/net/bluetooth/hci_core.h b/include/net/bluetooth/hci_core.h
index aa600fbf9a53..a5d82f9f3871 100644
--- a/include/net/bluetooth/hci_core.h
+++ b/include/net/bluetooth/hci_core.h
@@ -1733,6 +1733,7 @@ static inline struct hci_dev *hci_dev_hold(struct hci_dev *d)
 }
 
 #define hci_dev_lock(d)		mutex_lock(&d->lock)
+#define hci_dev_trylock(d)	mutex_trylock(&d->lock)
 #define hci_dev_unlock(d)	mutex_unlock(&d->lock)
 
 #define to_hci_dev(d) container_of(d, struct hci_dev, dev)
diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
index 1fbd52165fb2..1666601ebd1f 100644
--- a/net/bluetooth/l2cap_core.c
+++ b/net/bluetooth/l2cap_core.c
@@ -7498,13 +7498,29 @@ static void l2cap_connect_cfm(struct hci_conn *hcon, u8 status)
 
 int l2cap_disconn_ind(struct hci_conn *hcon)
 {
-	struct l2cap_conn *conn = hcon->l2cap_data;
+	struct hci_dev *hdev = hcon->hdev;
+	struct l2cap_conn *conn;
+	u8 reason = HCI_ERROR_REMOTE_USER_TERM;
 
 	BT_DBG("hcon %p", hcon);
 
-	if (!conn)
-		return HCI_ERROR_REMOTE_USER_TERM;
-	return conn->disc_reason;
+	/* l2cap_conn_del() is always called under hci_dev_lock(), so hold
+	 * it while dereferencing hcon->l2cap_data and reading disc_reason
+	 * to serialize against the free. trylock because hci_conn_del()
+	 * drains this worker with disable_delayed_work_sync() under
+	 * hci_dev_lock(), so a blocking lock here would deadlock against
+	 * that drain.
+	 */
+	if (!hci_dev_trylock(hdev))
+		return reason;
+
+	conn = hcon->l2cap_data;
+	if (conn)
+		reason = conn->disc_reason;
+
+	hci_dev_unlock(hdev);
+
+	return reason;
 }
 
 static void l2cap_disconn_cfm(struct hci_conn *hcon, u8 reason)
-- 
2.54.0

RE: Bluetooth: L2CAP: Fix slab-use-after-free in l2cap_disconn_ind

[bluez.test.bot]

[-- Attachment #1: Type: text/plain, Size: 2549 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=1118122

---Test result---

Test Summary:
CheckPatch                    PASS      1.22 seconds
VerifyFixes                   PASS      0.24 seconds
VerifySignedoff               PASS      0.30 seconds
GitLint                       PASS      0.63 seconds
SubjectPrefix                 PASS      0.21 seconds
BuildKernel                   PASS      27.16 seconds
CheckAllWarning               PASS      29.56 seconds
CheckSparse                   PASS      28.40 seconds
BuildKernel32                 PASS      26.30 seconds
CheckKernelLLVM               SKIP      0.00 seconds
TestRunnerSetup               PASS      497.73 seconds
TestRunner_l2cap-tester       PASS      59.17 seconds
TestRunner_iso-tester         PASS      76.47 seconds
TestRunner_bnep-tester        PASS      18.99 seconds
TestRunner_mgmt-tester        FAIL      209.55 seconds
TestRunner_rfcomm-tester      PASS      25.52 seconds
TestRunner_sco-tester         PASS      32.27 seconds
TestRunner_ioctl-tester       PASS      26.32 seconds
TestRunner_mesh-tester        FAIL      25.97 seconds
TestRunner_smp-tester         PASS      23.04 seconds
TestRunner_userchan-tester    PASS      19.91 seconds
TestRunner_6lowpan-tester     PASS      22.71 seconds
IncrementalBuild              PASS      25.67 seconds

Details
##############################
Test: CheckKernelLLVM - SKIP
Desc: Build kernel with LLVM + context analysis
Output:
Clang not found
##############################
Test: TestRunner_mgmt-tester - FAIL
Desc: Run mgmt-tester with test-runner
Output:
Total: 494, Passed: 487 (98.6%), Failed: 3, Not Run: 4

Failed Test Cases
Read Exp Feature - Success                           Failed       0.232 seconds
LL Privacy - Set Flags 2 (Enable RL)                 Failed       0.348 seconds
LL Privacy - Set Flags 3 (2 Devices to RL)           Failed       0.388 seconds
##############################
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    2.655 seconds
Mesh - Send cancel - 2                               Timed out    1.990 seconds


https://github.com/bluez/bluetooth-next/pull/367

---
Regards,
Linux Bluetooth