From: Yi Yang <yiyang13@xxxxxxxxxx>
commit 3c4f8333b582487a2d1e02171f1465531cde53e3 upstream.
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]
----------------------- -----------------------
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@xxxxxxxxxx>
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@xxxxxxxxxx>
Co-developed-by: Qiumiao Zhang <zhangqiumiao1@xxxxxxxxxx>
Signed-off-by: Qiumiao Zhang <zhangqiumiao1@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20230811031121.153237-1-yiyang13@xxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/tty/n_gsm.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -2481,12 +2481,13 @@ static void gsm_error(struct gsm_mux *gs
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);
