Re: [PATCH 1/2] bluetooth: hci_ldisc: fix NULL-pointer dereference on tty_close

[Marcel Holtmann <marcel@holtmann.org>]

Hi Johan,

> Do not close protocol driver until device has been unregistered.
> 
> This fixes a race between tty_close and hci_dev_open which can result in
> a NULL-pointer dereference.
> 
> The line discipline closes the protocol driver while we may still have
> hci_dev_open sleeping on the req_lock mutex resulting in a NULL-pointer
> dereference when lock is acquired and hci_init_req called.
> 
> Bug is 100% reproducible using hciattach and a disconnected serial port:
> 
> 0. # hciattach -n ttyO1 any noflow
> 
> 1. hci_dev_open called from hci_power_on grabs req lock
> 2. hci_init_req executes but device fails to initialise (times out
>    eventually)
> 3. hci_dev_open is called from hci_sock_ioctl and sleeps on req lock
> 4. hci_uart_tty_close detaches protocol driver and cancels init req
> 5. hci_dev_open (1) releases req lock
> 6. hci_dev_open (3) grabs req lock, calls hci_init_req, which triggers oops
>    when request is prepared in hci_uart_send_frame
> 
> [  137.201263] Unable to handle kernel NULL pointer dereference at virtual address 00000028
> [  137.209838] pgd = c0004000
> [  137.212677] [00000028] *pgd=00000000
> [  137.216430] Internal error: Oops: 17 [#1]
> [  137.220642] Modules linked in:
> [  137.223846] CPU: 0    Tainted: G        W     (3.3.0-rc6-dirty #406)
> [  137.230529] PC is at __lock_acquire+0x5c/0x1ab0
> [  137.235290] LR is at lock_acquire+0x9c/0x128
> [  137.239776] pc : [<c0071490>]    lr : [<c00733f8>]    psr: 20000093
> [  137.239776] sp : cf869dd8  ip : c0529554  fp : c051c730
> [  137.251800] r10: 00000000  r9 : cf8673c0  r8 : 00000080
> [  137.257293] r7 : 00000028  r6 : 00000002  r5 : 00000000  r4 : c053fd70
> [  137.264129] r3 : 00000000  r2 : 00000000  r1 : 00000000  r0 : 00000001
> [  137.270965] Flags: nzCv  IRQs off  FIQs on  Mode SVC_32  ISA ARM  Segment kernel
> [  137.278717] Control: 10c5387d  Table: 8f0f4019  DAC: 00000015
> [  137.284729] Process kworker/u:1 (pid: 7, stack limit = 0xcf8682e8)
> [  137.291229] Stack: (0xcf869dd8 to 0xcf86a000)
> [  137.295776] 9dc0:                                                       c0529554 00000000
> [  137.304351] 9de0: cf8673c0 cf868000 d03ea1ef cf868000 000001ef 00000470 00000000 00000002
> [  137.312927] 9e00: cf8673c0 00000001 c051c730 c00716ec 0000000c 00000440 c0529554 00000001
> [  137.321533] 9e20: c051c730 cf868000 d03ea1f3 00000000 c053b978 00000000 00000028 cf868000
> [  137.330078] 9e40: 00000000 00000000 00000002 00000000 00000000 c00733f8 00000002 00000080
> [  137.338684] 9e60: 00000000 c02a1d50 00000000 00000001 60000013 c0969a1c 60000093 c053b96c
> [  137.347259] 9e80: 00000002 00000018 20000013 c02a1d50 cf0ac000 00000000 00000002 cf868000
> [  137.355834] 9ea0: 00000089 c0374130 00000002 00000000 c02a1d50 cf0ac000 0000000c cf0fc540
> [  137.364410] 9ec0: 00000018 c02a1d50 cf0fc540 00000000 cf0fc540 c0282238 c028220c cf178d80
> [  137.372985] 9ee0: 127525d8 c02821cc 9a1fa451 c032727c 9a1fa451 127525d8 cf0fc540 cf0ac4ec
> [  137.381561] 9f00: cf0ac000 cf0fc540 cf0ac584 c03285f4 c0328580 cf0ac4ec cf85c740 c05510cc
> [  137.390136] 9f20: ce825400 c004c914 00000002 00000000 c004c884 ce8254f5 cf869f48 00000000
> [  137.398712] 9f40: c0328580 ce825415 c0a7f914 c061af64 00000000 c048cf3c cf8673c0 cf85c740
> [  137.407287] 9f60: c05510cc c051a66c c05510ec c05510c4 cf85c750 cf868000 00000089 c004d6ac
> [  137.415863] 9f80: 00000000 c0073d14 00000001 cf853ed8 cf85c740 c004d558 00000013 00000000
> [  137.424438] 9fa0: 00000000 00000000 00000000 c00516b0 00000000 00000000 cf85c740 00000000
> [  137.433013] 9fc0: 00000001 dead4ead ffffffff ffffffff c0551674 00000000 00000000 c0450aa4
> [  137.441589] 9fe0: cf869fe0 cf869fe0 cf853ed8 c005162c c0013b30 c0013b30 00ffff00 00ffff00
> [  137.450164] [<c0071490>] (__lock_acquire+0x5c/0x1ab0) from [<c00733f8>] (lock_acquire+0x9c/0x128)
> [  137.459503] [<c00733f8>] (lock_acquire+0x9c/0x128) from [<c0374130>] (_raw_spin_lock_irqsave+0x44/0x58)
> [  137.469360] [<c0374130>] (_raw_spin_lock_irqsave+0x44/0x58) from [<c02a1d50>] (skb_queue_tail+0x18/0x48)
> [  137.479339] [<c02a1d50>] (skb_queue_tail+0x18/0x48) from [<c0282238>] (h4_enqueue+0x2c/0x34)
> [  137.488189] [<c0282238>] (h4_enqueue+0x2c/0x34) from [<c02821cc>] (hci_uart_send_frame+0x34/0x68)
> [  137.497497] [<c02821cc>] (hci_uart_send_frame+0x34/0x68) from [<c032727c>] (hci_send_frame+0x50/0x88)
> [  137.507171] [<c032727c>] (hci_send_frame+0x50/0x88) from [<c03285f4>] (hci_cmd_work+0x74/0xd4)
> [  137.516204] [<c03285f4>] (hci_cmd_work+0x74/0xd4) from [<c004c914>] (process_one_work+0x1a0/0x4ec)
> [  137.525604] [<c004c914>] (process_one_work+0x1a0/0x4ec) from [<c004d6ac>] (worker_thread+0x154/0x344)
> [  137.535278] [<c004d6ac>] (worker_thread+0x154/0x344) from [<c00516b0>] (kthread+0x84/0x90)
> [  137.543975] [<c00516b0>] (kthread+0x84/0x90) from [<c0013b30>] (kernel_thread_exit+0x0/0x8)
> [  137.552734] Code: e59f4e5c e5941000 e3510000 0a000031 (e5971000)
> [  137.559234] ---[ end trace 1b75b31a2719ed1e ]---
> 
> Cc: stable <stable@vger.kernel.org>
> Signed-off-by: Johan Hovold <jhovold@gmail.com>
> ---
>  drivers/bluetooth/hci_ldisc.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/drivers/bluetooth/hci_ldisc.c b/drivers/bluetooth/hci_ldisc.c
> index 0711448..6946081 100644
> --- a/drivers/bluetooth/hci_ldisc.c
> +++ b/drivers/bluetooth/hci_ldisc.c
> @@ -310,11 +310,11 @@ static void hci_uart_tty_close(struct tty_struct *tty)
>  			hci_uart_close(hdev);
>  
>  		if (test_and_clear_bit(HCI_UART_PROTO_SET, &hu->flags)) {
> -			hu->proto->close(hu);
>  			if (hdev) {
>  				hci_unregister_dev(hdev);
>  				hci_free_dev(hdev);
>  			}
> +			hu->proto->close(hu);
>  		}
>  	}
>  }

what kernel version is this against? Our changes in bluetooth-next fixed
some of the destruct handling.

Also hci_unregister_dev should be calling the destruct handler and thus
your change is now accessing hu but it got freed already.

Regards

Marcel