tty: n_gsm: fix resource allocation order in gsm_activate_mux()

[ Upstream commit 7349660438603ed19282e75949561406531785a5 ]

Within gsm_activate_mux() all timers and locks are initiated before the
actual resource for the control channel is allocated. This can lead to race
conditions.

Allocate the control channel DLCI object first to avoid race conditions.

Fixes: e1eaea46bb40 ("tty: n_gsm line discipline")
Signed-off-by: Daniel Starke <daniel.starke@siemens.com>
Link: https://lore.kernel.org/r/20220701122332.2039-2-daniel.starke@siemens.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index ab7765afab86760d4be899debd254d759aeed7ef..17927163790ec3930c36f366210810c4a52e05f7 100644 (file)
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -2501,6 +2501,10 @@ static int gsm_activate_mux(struct gsm_mux *gsm)
        struct gsm_dlci *dlci;
        int ret;
 
+       dlci = gsm_dlci_alloc(gsm, 0);
+       if (dlci == NULL)
+               return -ENOMEM;
+
        timer_setup(&gsm->kick_timer, gsm_kick_timer, 0);
        timer_setup(&gsm->t2_timer, gsm_control_retransmit, 0);
        INIT_WORK(&gsm->tx_work, gsmld_write_task);
@@ -2517,9 +2521,6 @@ static int gsm_activate_mux(struct gsm_mux *gsm)
        if (ret)
                return ret;
 
-       dlci = gsm_dlci_alloc(gsm, 0);
-       if (dlci == NULL)
-               return -ENOMEM;
        gsm->has_devices = true;
        gsm->dead = false;              /* Tty opens are now permissible */
        return 0;