From 3c4f8333b582487a2d1e02171f1465531cde53e3 Mon Sep 17 00:00:00 2001
From: Yi Yang <yiyang13@huawei.com>
Date: Fri, 11 Aug 2023 11:11:21 +0800
Subject: [PATCH] tty: n_gsm: fix the UAF caused by race condition in gsm_cleanup_mux
Git-commit: 3c4f8333b582487a2d1e02171f1465531cde53e3
Patch-mainline: v6.5-rc7
References: git-fixes bsc#1218335 CVE-2023-6546
In commit 9b9c8195f3f0 ("tty: n_gsm: fix UAF in gsm_cleanup_mux"), the UAF
problem is not completely fixed. There is a race condition in
gsm_cleanup_mux(), which caused this UAF.
The UAF problem is triggered by the following race:
task[5046] task[5054]
Acked-by: Takashi Iwai <tiwai@suse.de>
----------------------- -----------------------
gsm_cleanup_mux();
dlci = gsm->dlci[0];
mutex_lock(&gsm->mutex);
gsm_cleanup_mux();
dlci = gsm->dlci[0]; //Didn't take the lock
gsm_dlci_release(gsm->dlci[i]);
gsm->dlci[i] = NULL;
mutex_unlock(&gsm->mutex);
mutex_lock(&gsm->mutex);
dlci->dead = true; //UAF
Fix it by assigning values after mutex_lock().
Link: https://syzkaller.appspot.com/text?tag=CrashReport&x=176188b5a80000
Cc: stable <stable@kernel.org>
Fixes: 9b9c8195f3f0 ("tty: n_gsm: fix UAF in gsm_cleanup_mux")
Fixes: aa371e96f05d ("tty: n_gsm: fix restart handling via CLD command")
Signed-off-by: Yi Yang <yiyang13@huawei.com>
Co-developed-by: Qiumiao Zhang <zhangqiumiao1@huawei.com>
Signed-off-by: Qiumiao Zhang <zhangqiumiao1@huawei.com>
Link: https://lore.kernel.org/r/20230811031121.153237-1-yiyang13@huawei.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/tty/n_gsm.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index 1cdefac4dd1b..739f522cb893 100644
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -3042,12 +3042,13 @@ static void gsm_error(struct gsm_mux *gsm)
static void gsm_cleanup_mux(struct gsm_mux *gsm, bool disc)
{
int i;
- struct gsm_dlci *dlci = gsm->dlci[0];
+ struct gsm_dlci *dlci;
struct gsm_msg *txq, *ntxq;
gsm->dead = true;
mutex_lock(&gsm->mutex);
+ dlci = gsm->dlci[0];
if (dlci) {
if (disc && dlci->state != DLCI_CLOSED) {
gsm_dlci_begin_close(dlci);
--
2.35.3