CVE-2021-4439

In the Linux kernel, the following vulnerability has been resolved: isdn:
cpai: check ctr->cnr to avoid array index out of bound 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]