CVE-2021-4439

In the Linux kernel, the following vulnerability has been resolved:<br /> <br /> isdn: cpai: check ctr-&gt;cnr to avoid array index out of bound<br /> <br /> The cmtp_add_connection() would add a cmtp session to a controller<br /> and run a kernel thread to process cmtp.<br /> <br /> __module_get(THIS_MODULE);<br /> session-&gt;task = kthread_run(cmtp_session, session, "kcmtpd_ctr_%d",<br /> session-&gt;num);<br /> <br /> During this process, the kernel thread would call detach_capi_ctr()<br /> to detach a register controller. if the controller<br /> was not attached yet, detach_capi_ctr() would<br /> trigger an array-index-out-bounds bug.<br /> <br /> [ 46.866069][ T6479] UBSAN: array-index-out-of-bounds in<br /> drivers/isdn/capi/kcapi.c:483:21<br /> [ 46.867196][ T6479] index -1 is out of range for type &amp;#39;capi_ctr *[32]&amp;#39;<br /> [ 46.867982][ T6479] CPU: 1 PID: 6479 Comm: kcmtpd_ctr_0 Not tainted<br /> 5.15.0-rc2+ #8<br /> [ 46.869002][ T6479] Hardware name: QEMU Standard PC (i440FX + PIIX,<br /> 1996), BIOS 1.14.0-2 04/01/2014<br /> [ 46.870107][ T6479] Call Trace:<br /> [ 46.870473][ T6479] dump_stack_lvl+0x57/0x7d<br /> [ 46.870974][ T6479] ubsan_epilogue+0x5/0x40<br /> [ 46.871458][ T6479] __ubsan_handle_out_of_bounds.cold+0x43/0x48<br /> [ 46.872135][ T6479] detach_capi_ctr+0x64/0xc0<br /> [ 46.872639][ T6479] cmtp_session+0x5c8/0x5d0<br /> [ 46.873131][ T6479] ? __init_waitqueue_head+0x60/0x60<br /> [ 46.873712][ T6479] ? cmtp_add_msgpart+0x120/0x120<br /> [ 46.874256][ T6479] kthread+0x147/0x170<br /> [ 46.874709][ T6479] ? set_kthread_struct+0x40/0x40<br /> [ 46.875248][ T6479] ret_from_fork+0x1f/0x30<br /> [ 46.875773][ T6479]