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From: Sungwoo Kim <iam@sung-woo.kim>
To: 
Cc: daveti@purdue.edu,
	dan.carpenter@linaro.org,
	Sungwoo Kim <iam@sung-woo.kim>,
	Marcel Holtmann <marcel@holtmann.org>,
	Johan Hedberg <johan.hedberg@gmail.com>,
	Luiz Augusto von Dentz <luiz.dentz@gmail.com>,
	linux-bluetooth@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: [PATCH v3] Bluetooth: L2CAP: Fix slab-use-after-free in l2cap_connect()
Date: Tue, 30 Apr 2024 02:32:10 -0400
Message-Id: <20240430063209.584244-1-iam@sung-woo.kim>
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MIME-Version: 1.0
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Extend a critical section to prevent chan from early freeing.
Also make the l2cap_connect() return type void. Nothing is using the
returned value but it is ugly to return a potentially freed pointer.
Making it void will help with backports because earlier kernels did use
the return value. Now the compile will break for kernels where this
patch is not a complete fix.

The patch is copied from
https://gist.github.com/Vudentz/c0c09ca0eff64a32ca50b1a6eb41295d

Thank you for your help, Dan and Luiz.

Call stack summary:

[use]
l2cap_bredr_sig_cmd
  l2cap_connect
  ┌ mutex_lock(&conn->chan_lock);
  │ chan = pchan->ops->new_connection(pchan); <- alloc chan
  │ __l2cap_chan_add(conn, chan);
  │   l2cap_chan_hold(chan);
  │   list_add(&chan->list, &conn->chan_l);   ... (1)
  └ mutex_unlock(&conn->chan_lock);
    chan->conf_state              ... (4) <- use after free

[free]
l2cap_conn_del
┌ mutex_lock(&conn->chan_lock);
│ foreach chan in conn->chan_l:            ... (2)
│   l2cap_chan_put(chan);
│     l2cap_chan_destroy
│       kfree(chan)               ... (3) <- chan freed
└ mutex_unlock(&conn->chan_lock);

==================================================================
BUG: KASAN: slab-use-after-free in instrument_atomic_read include/linux/instrumented.h:68 [inline]
BUG: KASAN: slab-use-after-free in _test_bit include/asm-generic/bitops/instrumented-non-atomic.h:141 [inline]
BUG: KASAN: slab-use-after-free in l2cap_connect+0xa67/0x11a0 net/bluetooth/l2cap_core.c:4260
Read of size 8 at addr ffff88810bf040a0 by task kworker/u3:1/311

CPU: 0 PID: 311 Comm: kworker/u3:1 Not tainted 6.8.0+ #61
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
Workqueue: hci0 hci_rx_work
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x85/0xb0 lib/dump_stack.c:106
 print_address_description mm/kasan/report.c:377 [inline]
 print_report+0x18f/0x560 mm/kasan/report.c:488
 kasan_report+0xd7/0x110 mm/kasan/report.c:601
 kasan_check_range+0x262/0x2f0 mm/kasan/generic.c:189
 __kasan_check_read+0x15/0x20 mm/kasan/shadow.c:31
 instrument_atomic_read include/linux/instrumented.h:68 [inline]
 _test_bit include/asm-generic/bitops/instrumented-non-atomic.h:141 [inline]
 l2cap_connect+0xa67/0x11a0 net/bluetooth/l2cap_core.c:4260
 l2cap_bredr_sig_cmd+0x17fe/0x9a70
 l2cap_sig_channel net/bluetooth/l2cap_core.c:6539 [inline]
 l2cap_recv_frame+0x82e/0x86a0 net/bluetooth/l2cap_core.c:7818
 l2cap_recv_acldata+0x379/0xbe0 net/bluetooth/l2cap_core.c:8536
 hci_acldata_packet net/bluetooth/hci_core.c:3876 [inline]
 hci_rx_work+0x64b/0xcb0 net/bluetooth/hci_core.c:4111
 process_one_work kernel/workqueue.c:2633 [inline]
 process_scheduled_works+0x6b9/0xdc0 kernel/workqueue.c:2706
 worker_thread+0xb2b/0x13d0 kernel/workqueue.c:2787
 kthread+0x2a9/0x340 kernel/kthread.c:388
 ret_from_fork+0x5c/0x90 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x1b/0x30 arch/x86/entry/entry_64.S:243
 </TASK>

Allocated by task 311:
 kasan_save_stack mm/kasan/common.c:47 [inline]
 kasan_save_track+0x30/0x70 mm/kasan/common.c:68
 kasan_save_alloc_info+0x3c/0x50 mm/kasan/generic.c:575
 poison_kmalloc_redzone mm/kasan/common.c:370 [inline]
 __kasan_kmalloc+0xa2/0xc0 mm/kasan/common.c:387
 kasan_kmalloc include/linux/kasan.h:211 [inline]
 kmalloc_trace+0x1c9/0x390 mm/slub.c:4012
 kmalloc include/linux/slab.h:590 [inline]
 kzalloc include/linux/slab.h:711 [inline]
 l2cap_chan_create+0x59/0xc80 net/bluetooth/l2cap_core.c:466
 l2cap_sock_alloc net/bluetooth/l2cap_sock.c:1849 [inline]
 l2cap_sock_new_connection_cb+0x14d/0x2a0 net/bluetooth/l2cap_sock.c:1457
 l2cap_connect+0x329/0x11a0 net/bluetooth/l2cap_core.c:4176
 l2cap_bredr_sig_cmd+0x17fe/0x9a70
 l2cap_sig_channel net/bluetooth/l2cap_core.c:6539 [inline]
 l2cap_recv_frame+0x82e/0x86a0 net/bluetooth/l2cap_core.c:7818
 l2cap_recv_acldata+0x379/0xbe0 net/bluetooth/l2cap_core.c:8536
 hci_acldata_packet net/bluetooth/hci_core.c:3876 [inline]
 hci_rx_work+0x64b/0xcb0 net/bluetooth/hci_core.c:4111
 process_one_work kernel/workqueue.c:2633 [inline]
 process_scheduled_works+0x6b9/0xdc0 kernel/workqueue.c:2706
 worker_thread+0xb2b/0x13d0 kernel/workqueue.c:2787
 kthread+0x2a9/0x340 kernel/kthread.c:388
 ret_from_fork+0x5c/0x90 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x1b/0x30 arch/x86/entry/entry_64.S:243

Freed by task 66:
 kasan_save_stack mm/kasan/common.c:47 [inline]
 kasan_save_track+0x30/0x70 mm/kasan/common.c:68
 kasan_save_free_info+0x44/0x50 mm/kasan/generic.c:589
 poison_slab_object+0x11a/0x190 mm/kasan/common.c:240
 __kasan_slab_free+0x3b/0x60 mm/kasan/common.c:256
 kasan_slab_free include/linux/kasan.h:184 [inline]
 slab_free_hook mm/slub.c:2121 [inline]
 slab_free mm/slub.c:4299 [inline]
 kfree+0x106/0x2e0 mm/slub.c:4409
 l2cap_chan_destroy net/bluetooth/l2cap_core.c:509 [inline]
 kref_put include/linux/kref.h:65 [inline]
 l2cap_chan_put+0x1e7/0x2b0 net/bluetooth/l2cap_core.c:533
 l2cap_conn_del+0x38e/0x5f0 net/bluetooth/l2cap_core.c:1929
 l2cap_connect_cfm+0xc2/0x11e0 net/bluetooth/l2cap_core.c:8254
 hci_connect_cfm include/net/bluetooth/hci_core.h:1986 [inline]
 hci_conn_failed+0x202/0x370 net/bluetooth/hci_conn.c:1289
 hci_abort_conn_sync+0x913/0xae0 net/bluetooth/hci_sync.c:5359
 abort_conn_sync+0xda/0x110 net/bluetooth/hci_conn.c:2988
 hci_cmd_sync_work+0x20d/0x3e0 net/bluetooth/hci_sync.c:306
 process_one_work kernel/workqueue.c:2633 [inline]
 process_scheduled_works+0x6b9/0xdc0 kernel/workqueue.c:2706
 worker_thread+0xb2b/0x13d0 kernel/workqueue.c:2787
 kthread+0x2a9/0x340 kernel/kthread.c:388
 ret_from_fork+0x5c/0x90 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x1b/0x30 arch/x86/entry/entry_64.S:243

The buggy address belongs to the object at ffff88810bf04000
 which belongs to the cache kmalloc-1k of size 1024
The buggy address is located 160 bytes inside of
 freed 1024-byte region [ffff88810bf04000, ffff88810bf04400)

The buggy address belongs to the physical page:
page:00000000567b7faa refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x10bf04
head:00000000567b7faa order:2 entire_mapcount:0 nr_pages_mapped:0 pincount:0
anon flags: 0x17ffffc0000840(slab|head|node=0|zone=2|lastcpupid=0x1fffff)
page_type: 0xffffffff()
raw: 0017ffffc0000840 ffff888100041dc0 0000000000000000 0000000000000001
raw: 0000000000000000 0000000080080008 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff88810bf03f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88810bf04000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff88810bf04080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                               ^
 ffff88810bf04100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88810bf04180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

Fixes: 73ffa904b782 ("Bluetooth: Move conf_{req,rsp} stuff to struct l2cap_chan")
Signed-off-by: Sungwoo Kim <iam@sung-woo.kim>
---
V1 -> V2:
Make l2cap_connect() return void.
Fix a wrong stack trace attached.

V2 -> V3:
Extend a lock instead of additional hold and lock

 net/bluetooth/l2cap_core.c | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
index 84fc70862..eeba16f69 100644
--- a/net/bluetooth/l2cap_core.c
+++ b/net/bluetooth/l2cap_core.c
@@ -3902,13 +3902,13 @@ static inline int l2cap_command_rej(struct l2cap_conn *conn,
 	return 0;
 }
 
-static struct l2cap_chan *l2cap_connect(struct l2cap_conn *conn,
+static void l2cap_connect(struct l2cap_conn *conn,
 					struct l2cap_cmd_hdr *cmd,
 					u8 *data, u8 rsp_code, u8 amp_id)
 {
 	struct l2cap_conn_req *req = (struct l2cap_conn_req *) data;
 	struct l2cap_conn_rsp rsp;
-	struct l2cap_chan *chan = NULL, *pchan;
+	struct l2cap_chan *chan = NULL, *pchan = NULL;
 	int result, status = L2CAP_CS_NO_INFO;
 
 	u16 dcid = 0, scid = __le16_to_cpu(req->scid);
@@ -3921,7 +3921,7 @@ static struct l2cap_chan *l2cap_connect(struct l2cap_conn *conn,
 					 &conn->hcon->dst, ACL_LINK);
 	if (!pchan) {
 		result = L2CAP_CR_BAD_PSM;
-		goto sendresp;
+		goto response;
 	}
 
 	mutex_lock(&conn->chan_lock);
@@ -4008,17 +4008,15 @@ static struct l2cap_chan *l2cap_connect(struct l2cap_conn *conn,
 	}
 
 response:
-	l2cap_chan_unlock(pchan);
-	mutex_unlock(&conn->chan_lock);
-	l2cap_chan_put(pchan);
-
-sendresp:
 	rsp.scid   = cpu_to_le16(scid);
 	rsp.dcid   = cpu_to_le16(dcid);
 	rsp.result = cpu_to_le16(result);
 	rsp.status = cpu_to_le16(status);
 	l2cap_send_cmd(conn, cmd->ident, rsp_code, sizeof(rsp), &rsp);
 
+	if (!pchan)
+		return;
+
 	if (result == L2CAP_CR_PEND && status == L2CAP_CS_NO_INFO) {
 		struct l2cap_info_req info;
 		info.type = cpu_to_le16(L2CAP_IT_FEAT_MASK);
@@ -4041,7 +4039,9 @@ static struct l2cap_chan *l2cap_connect(struct l2cap_conn *conn,
 		chan->num_conf_req++;
 	}
 
-	return chan;
+	l2cap_chan_unlock(pchan);
+	mutex_unlock(&conn->chan_lock);
+	l2cap_chan_put(pchan);
 }
 
 static int l2cap_connect_req(struct l2cap_conn *conn,
-- 
2.34.1