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    Subject[PATCH 5.4 42/58] isdn: cpai: check ctr->cnr to avoid array index out of bound
    Date
    From: Xiaolong Huang <butterflyhuangxx@gmail.com>

    commit 1f3e2e97c003f80c4b087092b225c8787ff91e4d upstream.

    The cmtp_add_connection() would add a cmtp session to a controller
    and run a kernel thread to process cmtp.

    __module_get(THIS_MODULE);
    session->task = kthread_run(cmtp_session, session, "kcmtpd_ctr_%d",
    session->num);

    During this process, the kernel thread would call detach_capi_ctr()
    to detach a register controller. if the controller
    was not attached yet, detach_capi_ctr() would
    trigger an array-index-out-bounds bug.

    [ 46.866069][ T6479] UBSAN: array-index-out-of-bounds in
    drivers/isdn/capi/kcapi.c:483:21
    [ 46.867196][ T6479] index -1 is out of range for type 'capi_ctr *[32]'
    [ 46.867982][ T6479] CPU: 1 PID: 6479 Comm: kcmtpd_ctr_0 Not tainted
    5.15.0-rc2+ #8
    [ 46.869002][ T6479] Hardware name: QEMU Standard PC (i440FX + PIIX,
    1996), BIOS 1.14.0-2 04/01/2014
    [ 46.870107][ T6479] Call Trace:
    [ 46.870473][ T6479] dump_stack_lvl+0x57/0x7d
    [ 46.870974][ T6479] ubsan_epilogue+0x5/0x40
    [ 46.871458][ T6479] __ubsan_handle_out_of_bounds.cold+0x43/0x48
    [ 46.872135][ T6479] detach_capi_ctr+0x64/0xc0
    [ 46.872639][ T6479] cmtp_session+0x5c8/0x5d0
    [ 46.873131][ T6479] ? __init_waitqueue_head+0x60/0x60
    [ 46.873712][ T6479] ? cmtp_add_msgpart+0x120/0x120
    [ 46.874256][ T6479] kthread+0x147/0x170
    [ 46.874709][ T6479] ? set_kthread_struct+0x40/0x40
    [ 46.875248][ T6479] ret_from_fork+0x1f/0x30
    [ 46.875773][ T6479]

    Signed-off-by: Xiaolong Huang <butterflyhuangxx@gmail.com>
    Acked-by: Arnd Bergmann <arnd@arndb.de>
    Link: https://lore.kernel.org/r/20211008065830.305057-1-butterflyhuangxx@gmail.com
    Signed-off-by: Jakub Kicinski <kuba@kernel.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    drivers/isdn/capi/kcapi.c | 5 +++++
    1 file changed, 5 insertions(+)

    --- a/drivers/isdn/capi/kcapi.c
    +++ b/drivers/isdn/capi/kcapi.c
    @@ -565,6 +565,11 @@ int detach_capi_ctr(struct capi_ctr *ctr

    ctr_down(ctr, CAPI_CTR_DETACHED);

    + if (ctr->cnr < 1 || ctr->cnr - 1 >= CAPI_MAXCONTR) {
    + err = -EINVAL;
    + goto unlock_out;
    + }
    +
    if (capi_controller[ctr->cnr - 1] != ctr) {
    err = -EINVAL;
    goto unlock_out;

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