From: Yi Yang yiyang13@huawei.com
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@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(-)
--- a/drivers/tty/n_gsm.c +++ b/drivers/tty/n_gsm.c @@ -3042,12 +3042,13 @@ 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);