Commit 3c4f8333 authored by Yi Yang's avatar Yi Yang Committed by Greg Kroah-Hartman
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tty: n_gsm: fix the UAF caused by race condition in gsm_cleanup_mux 

In commit 9b9c8195 ("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]
-----------------------        -----------------------
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: 9b9c8195 ("tty: n_gsm: fix UAF in gsm_cleanup_mux")
Fixes: aa371e96 ("tty: n_gsm: fix restart handling via CLD command")
Signed-off-by: default avatarYi Yang <yiyang13@huawei.com>
Co-developed-by: default avatarQiumiao Zhang <zhangqiumiao1@huawei.com>
Signed-off-by: default avatarQiumiao Zhang <zhangqiumiao1@huawei.com>
Link: https://lore.kernel.org/r/20230811031121.153237-1-yiyang13@huawei.com


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent a4a79e03

drivers/tty/n_gsm.c

+2 −1
Original line number Diff line number Diff line
@@ -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);