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    Subject[PATCH 2/2] bluetooth: hci_core: fix NULL-pointer dereference at unregister
    Date
    Make sure hci_dev_open returns immediately if hci_dev_unregister has
    been called.

    This fixes a race between hci_dev_open and hci_dev_unregister which can
    lead to a NULL-pointer dereference.

    Bug is 100% reproducible using hciattach and a disconnected serial port:

    0. # hciattach -n /dev/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 calls hci_dev_unregister and sleeps on req lock in
    hci_dev_do_close
    5. hci_dev_open (1) releases req lock
    6. hci_dev_do_close grabs req lock and returns as device is not up
    7. hci_dev_unregister sleeps in destroy_workqueue
    8. hci_dev_open (3) grabs req lock, calls hci_init_req and eventually sleeps
    9. hci_dev_unregister finishes, while hci_dev_open is still running...

    [ 79.627136] INFO: trying to register non-static key.
    [ 79.632354] the code is fine but needs lockdep annotation.
    [ 79.638122] turning off the locking correctness validator.
    [ 79.643920] [<c00188bc>] (unwind_backtrace+0x0/0xf8) from [<c00729c4>] (__lock_acquire+0x1590/0x1ab0)
    [ 79.653594] [<c00729c4>] (__lock_acquire+0x1590/0x1ab0) from [<c00733f8>] (lock_acquire+0x9c/0x128)
    [ 79.663085] [<c00733f8>] (lock_acquire+0x9c/0x128) from [<c0040a88>] (run_timer_softirq+0x150/0x3ac)
    [ 79.672668] [<c0040a88>] (run_timer_softirq+0x150/0x3ac) from [<c003a3b8>] (__do_softirq+0xd4/0x22c)
    [ 79.682281] [<c003a3b8>] (__do_softirq+0xd4/0x22c) from [<c003a924>] (irq_exit+0x8c/0x94)
    [ 79.690856] [<c003a924>] (irq_exit+0x8c/0x94) from [<c0013a50>] (handle_IRQ+0x34/0x84)
    [ 79.699157] [<c0013a50>] (handle_IRQ+0x34/0x84) from [<c0008530>] (omap3_intc_handle_irq+0x48/0x4c)
    [ 79.708648] [<c0008530>] (omap3_intc_handle_irq+0x48/0x4c) from [<c037499c>] (__irq_usr+0x3c/0x60)
    [ 79.718048] Exception stack(0xcf281fb0 to 0xcf281ff8)
    [ 79.723358] 1fa0: 0001e6a0 be8dab00 0001e698 00036698
    [ 79.731933] 1fc0: 0002df98 0002df38 0000001f 00000000 b6f234d0 00000000 00000004 00000000
    [ 79.740509] 1fe0: 0001e6f8 be8d6aa0 be8dac50 0000aab8 80000010 ffffffff
    [ 79.747497] Unable to handle kernel NULL pointer dereference at virtual address 00000000
    [ 79.756011] pgd = cf3b4000
    [ 79.758850] [00000000] *pgd=8f0c7831, *pte=00000000, *ppte=00000000
    [ 79.765502] Internal error: Oops: 80000007 [#1]
    [ 79.770294] Modules linked in:
    [ 79.773529] CPU: 0 Tainted: G W (3.3.0-rc6-00002-gb5d5c87 #421)
    [ 79.781066] PC is at 0x0
    [ 79.783721] LR is at run_timer_softirq+0x16c/0x3ac
    [ 79.788787] pc : [<00000000>] lr : [<c0040aa4>] psr: 60000113
    [ 79.788787] sp : cf281ee0 ip : 00000000 fp : cf280000
    [ 79.800903] r10: 00000004 r9 : 00000100 r8 : b6f234d0
    [ 79.806427] r7 : c0519c28 r6 : cf093488 r5 : c0561a00 r4 : 00000000
    [ 79.813323] r3 : 00000000 r2 : c054eee0 r1 : 00000001 r0 : 00000000
    [ 79.820190] Flags: nZCv IRQs on FIQs on Mode SVC_32 ISA ARM Segment user
    [ 79.827728] Control: 10c5387d Table: 8f3b4019 DAC: 00000015
    [ 79.833801] Process gpsd (pid: 1265, stack limit = 0xcf2802e8)
    [ 79.839965] Stack: (0xcf281ee0 to 0xcf282000)
    [ 79.844573] 1ee0: 00000002 00000000 c0040a24 00000000 00000002 cf281f08 00200200 00000000
    [ 79.853210] 1f00: 00000000 cf281f18 cf281f08 00000000 00000000 00000000 cf281f18 cf281f18
    [ 79.861816] 1f20: 00000000 00000001 c056184c 00000000 00000001 b6f234d0 c0561848 00000004
    [ 79.870452] 1f40: cf280000 c003a3b8 c051e79c 00000001 00000000 00000100 3fa9e7b8 0000000a
    [ 79.879089] 1f60: 00000025 cf280000 00000025 00000000 00000000 b6f234d0 00000000 00000004
    [ 79.887756] 1f80: 00000000 c003a924 c053ad38 c0013a50 fa200000 cf281fb0 ffffffff c0008530
    [ 79.896362] 1fa0: 0001e6a0 0000aab8 80000010 c037499c 0001e6a0 be8dab00 0001e698 00036698
    [ 79.904998] 1fc0: 0002df98 0002df38 0000001f 00000000 b6f234d0 00000000 00000004 00000000
    [ 79.913665] 1fe0: 0001e6f8 be8d6aa0 be8dac50 0000aab8 80000010 ffffffff 00fbf700 04ffff00
    [ 79.922302] [<c0040aa4>] (run_timer_softirq+0x16c/0x3ac) from [<c003a3b8>] (__do_softirq+0xd4/0x22c)
    [ 79.931945] [<c003a3b8>] (__do_softirq+0xd4/0x22c) from [<c003a924>] (irq_exit+0x8c/0x94)
    [ 79.940582] [<c003a924>] (irq_exit+0x8c/0x94) from [<c0013a50>] (handle_IRQ+0x34/0x84)
    [ 79.948913] [<c0013a50>] (handle_IRQ+0x34/0x84) from [<c0008530>] (omap3_intc_handle_irq+0x48/0x4c)
    [ 79.958404] [<c0008530>] (omap3_intc_handle_irq+0x48/0x4c) from [<c037499c>] (__irq_usr+0x3c/0x60)
    [ 79.967773] Exception stack(0xcf281fb0 to 0xcf281ff8)
    [ 79.973083] 1fa0: 0001e6a0 be8dab00 0001e698 00036698
    [ 79.981658] 1fc0: 0002df98 0002df38 0000001f 00000000 b6f234d0 00000000 00000004 00000000
    [ 79.990234] 1fe0: 0001e6f8 be8d6aa0 be8dac50 0000aab8 80000010 ffffffff
    [ 79.997161] Code: bad PC value
    [ 80.000396] ---[ end trace 6f6739840475f9ee ]---
    [ 80.005279] Kernel panic - not syncing: Fatal exception in interrupt

    Cc: stable <stable@vger.kernel.org>
    Signed-off-by: Johan Hovold <jhovold@gmail.com>
    ---
    include/net/bluetooth/hci.h | 1 +
    net/bluetooth/hci_core.c | 7 +++++++
    2 files changed, 8 insertions(+), 0 deletions(-)

    diff --git a/include/net/bluetooth/hci.h b/include/net/bluetooth/hci.h
    index 00596e8..f626f44 100644
    --- a/include/net/bluetooth/hci.h
    +++ b/include/net/bluetooth/hci.h
    @@ -86,6 +86,7 @@ enum {
    HCI_DEBUG_KEYS,

    HCI_RESET,
    + HCI_UNREGISTER,
    };

    /*
    diff --git a/net/bluetooth/hci_core.c b/net/bluetooth/hci_core.c
    index 5aeb624..3937ce3 100644
    --- a/net/bluetooth/hci_core.c
    +++ b/net/bluetooth/hci_core.c
    @@ -525,6 +525,11 @@ int hci_dev_open(__u16 dev)

    hci_req_lock(hdev);

    + if (test_bit(HCI_UNREGISTER, &hdev->flags)) {
    + ret = -ENODEV;
    + goto done;
    + }
    +
    if (hdev->rfkill && rfkill_blocked(hdev->rfkill)) {
    ret = -ERFKILL;
    goto done;
    @@ -1577,6 +1582,8 @@ void hci_unregister_dev(struct hci_dev *hdev)

    BT_DBG("%p name %s bus %d", hdev, hdev->name, hdev->bus);

    + set_bit(HCI_UNREGISTER, &hdev->flags);
    +
    write_lock(&hci_dev_list_lock);
    list_del(&hdev->list);
    write_unlock(&hci_dev_list_lock);
    --
    1.7.8.4


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