Re: [PATCH v2] Bluetooth: L2CAP: Fix slab-use-after-free in l2cap_connect()

[Sungwoo Kim <iam@sung-woo.kim>]

Hi Luiz,

On Mon, Apr 29, 2024 at 1:03 PM Luiz Augusto von Dentz
<luiz.dentz@gmail.com> wrote:
>
> Hi Kim,
>
> On Sat, Apr 27, 2024 at 1:44 PM Sungwoo Kim <iam@sung-woo.kim> wrote:
> >
> > Add an hold and lock the channel at l2cap_connect() to avoid use after free.
> > 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 i 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.
> >
> > Thank you for your help, Dan.
> >
> > 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);
>
> Sounds like we didn't even respond so I do wonder why we are releasing
> the 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.
> >
> >  net/bluetooth/l2cap_core.c | 10 ++++++++--
> >  1 file changed, 8 insertions(+), 2 deletions(-)
> >
> > diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
> > index 84fc70862..e7c18267c 100644
> > --- a/net/bluetooth/l2cap_core.c
> > +++ b/net/bluetooth/l2cap_core.c
> > @@ -3902,7 +3902,7 @@ 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)
> >  {
> > @@ -3953,6 +3953,9 @@ static struct l2cap_chan *l2cap_connect(struct l2cap_conn *conn,
> >         if (!chan)
> >                 goto response;
> >
> > +       l2cap_chan_hold(chan);
> > +       l2cap_chan_lock(chan);
> > +
> >         /* For certain devices (ex: HID mouse), support for authentication,
> >          * pairing and bonding is optional. For such devices, inorder to avoid
> >          * the ACL alive for too long after L2CAP disconnection, reset the ACL
> > @@ -4041,7 +4044,10 @@ static struct l2cap_chan *l2cap_connect(struct l2cap_conn *conn,
> >                 chan->num_conf_req++;
> >         }
> >
> > -       return chan;
> > +       if (chan) {
> > +               l2cap_chan_unlock(chan);
> > +               l2cap_chan_put(chan);
> > +       }
> >  }
> >
> >  static int l2cap_connect_req(struct l2cap_conn *conn,
> > --
> > 2.34.1
> >
>
> How about we do something like:
>
> https://gist.github.com/Vudentz/c0c09ca0eff64a32ca50b1a6eb41295d

Looks awesome to me. I'll send a v3 patch soon.

>
> --
> Luiz Augusto von Dentz
>