From: Xiaolong Huang butterflyhuangxx@gmail.com

stable inclusion from linux-4.19.214 commit 7d91adc0ccb060ce564103315189466eb822cc6a CVE: CVE-2021-3896

--------------------------------

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 Signed-off-by: Rui Xiang rui.xiang@huawei.com Signed-off-by: Yang Yingliang yangyingliang@huawei.com --- drivers/isdn/capi/kcapi.c | 5 +++++ 1 file changed, 5 insertions(+)

diff --git a/drivers/isdn/capi/kcapi.c b/drivers/isdn/capi/kcapi.c index a4ceb61c5b603..ed9ee2bbf232e 100644 --- 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;