Re: [PATCH] isdn: cpai: check ctr->cnr to avoid array index out of bound

[Arnd Bergmann]

On Fri, Oct 8, 2021 at 8:58 AM Xiaolong Huang
<butterflyhuangxx@xxxxxxxxx> wrote:
>
> 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@xxxxxxxxx>

Acked-by: Arnd Bergmann <arnd@xxxxxxxx>