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]

References

• https://nvd.nist.gov/vuln/detail/CVE-2021-4439
• https://git.kernel.org/stable/c/1f3e2e97c003f80c4b087092b225c8787ff91e4d
• https://git.kernel.org/stable/c/24219a977bfe3d658687e45615c70998acdbac5a
• https://git.kernel.org/stable/c/285e9210b1fab96a11c0be3ed5cea9dd48b6ac54
• https://git.kernel.org/stable/c/7d91adc0ccb060ce564103315189466eb822cc6a
• https://git.kernel.org/stable/c/7f221ccbee4ec662e2292d490a43ce6c314c4594
• https://git.kernel.org/stable/c/9b6b2db77bc3121fe435f1d4b56e34de443bec75
• https://git.kernel.org/stable/c/cc20226e218a2375d50dd9ac14fb4121b43375ff
• https://git.kernel.org/stable/c/e8b8de17e164c9f1b7777f1c6f99d05539000036