Re: [PATCH] Bluetooth: check for zapped sk before connecting

[Archie Pusaka]

Hi Marcel,

Thanks for your suggestion. I implemented it in v2, please take another look.


On Mon, 22 Mar 2021 at 23:53, Marcel Holtmann <marcel@xxxxxxxxxxxx> wrote:
>
> Hi Archie,
>
> > There is a possibility of receiving a zapped sock on
> > l2cap_sock_connect(). This could lead to interesting crashes, one
> > such case is tearing down an already tore l2cap_sock as is happened
> > with this call trace:
> >
> > __dump_stack lib/dump_stack.c:15 [inline]
> > dump_stack+0xc4/0x118 lib/dump_stack.c:56
> > register_lock_class kernel/locking/lockdep.c:792 [inline]
> > register_lock_class+0x239/0x6f6 kernel/locking/lockdep.c:742
> > __lock_acquire+0x209/0x1e27 kernel/locking/lockdep.c:3105
> > lock_acquire+0x29c/0x2fb kernel/locking/lockdep.c:3599
> > __raw_spin_lock_bh include/linux/spinlock_api_smp.h:137 [inline]
> > _raw_spin_lock_bh+0x38/0x47 kernel/locking/spinlock.c:175
> > spin_lock_bh include/linux/spinlock.h:307 [inline]
> > lock_sock_nested+0x44/0xfa net/core/sock.c:2518
> > l2cap_sock_teardown_cb+0x88/0x2fb net/bluetooth/l2cap_sock.c:1345
> > l2cap_chan_del+0xa3/0x383 net/bluetooth/l2cap_core.c:598
> > l2cap_chan_close+0x537/0x5dd net/bluetooth/l2cap_core.c:756
> > l2cap_chan_timeout+0x104/0x17e net/bluetooth/l2cap_core.c:429
> > process_one_work+0x7e3/0xcb0 kernel/workqueue.c:2064
> > worker_thread+0x5a5/0x773 kernel/workqueue.c:2196
> > kthread+0x291/0x2a6 kernel/kthread.c:211
> > ret_from_fork+0x4e/0x80 arch/x86/entry/entry_64.S:604
> >
> > Signed-off-by: Archie Pusaka <apusaka@xxxxxxxxxxxx>
> > Reported-by: syzbot+abfc0f5e668d4099af73@xxxxxxxxxxxxxxxxxxxxxxxxx
> > Reviewed-by: Alain Michaud <alainm@xxxxxxxxxxxx>
> > Reviewed-by: Abhishek Pandit-Subedi <abhishekpandit@xxxxxxxxxxxx>
> > Reviewed-by: Guenter Roeck <groeck@xxxxxxxxxxxx>
> > ---
> >
> > net/bluetooth/l2cap_sock.c | 7 +++++++
> > 1 file changed, 7 insertions(+)
> >
> > diff --git a/net/bluetooth/l2cap_sock.c b/net/bluetooth/l2cap_sock.c
> > index f1b1edd0b697..b86fd8cc4dc1 100644
> > --- a/net/bluetooth/l2cap_sock.c
> > +++ b/net/bluetooth/l2cap_sock.c
> > @@ -182,6 +182,13 @@ static int l2cap_sock_connect(struct socket *sock, struct sockaddr *addr,
> >
> >       BT_DBG("sk %p", sk);
> >
> > +     lock_sock(sk);
> > +     if (sock_flag(sk, SOCK_ZAPPED)) {
> > +             release_sock(sk);
> > +             return -EINVAL;
> > +     }
> > +     release_sock(sk);
> > +
>
> hmmm. I wonder if this would look better and easy to see that the locking is done correctly.
>
>         lock_sock(sk);
>         zapped = sock_flag(sk, SOCK_ZAPPED);
>         release_sock(sk);
>
>         if (zapped)
>                 return -EINVAL;
>
> Regards
>
> Marcel
>