Hi, I make a patch for this issue.
Regards,
butt3rflyh4ck.
On Fri, Sep 24, 2021 at 6:02 PM butt3rflyh4ck
<butterflyhuangxx@xxxxxxxxx> wrote:
>
> > When I last touched the capi code, I tried to remove it all, but we then
> > left it in the kernel because the bluetooth cmtp code can still theoretically
> > use it.
> >
> > May I ask how you managed to run into this? Did you find the bug through
> > inspection first and then produce it using cmtp, or did you actually use
> > cmtp?
>
> I fuzz the bluez system and find a crash to analyze it and reproduce it.
>
> > If the only purpose of cmtp is now to be a target for exploits, then I
> > would suggest we consider removing both cmtp and capi for
> > good after backporting your fix to stable kernels. Obviously
> > if it turns out that someone actually uses cmtp and/or capi, we
> > should not remove it.
> >
> Yes, I think this should be feasible.
>
> Regards
> butt3rflyh4ck.
>
>
> --
> Active Defense Lab of Venustech
--
Active Defense Lab of Venustech
From 15449bb5aac1f828dc82054651fe8f4dca37bef7 Mon Sep 17 00:00:00 2001
From: Xiaolong Huang <butterflyhuangxx@xxxxxxxxx>
Date: Tue, 28 Sep 2021 13:03:41 +0800
Subject: [PATCH] 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]
Signed-off-by: Xiaolong Huang <butterflyhuangxx@xxxxxxxxx>
---
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 cb0afe897162..7313454e403a 100644
--- a/drivers/isdn/capi/kcapi.c
+++ b/drivers/isdn/capi/kcapi.c
@@ -480,6 +480,11 @@ 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;
--
2.25.1
