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[v5,2/2] tty: n_gsm: fix resource allocation order in gsm_activate_mux()

Message ID 20220701122332.2039-2-daniel.starke@siemens.com
State New
Headers show
Series [v5,1/2] tty: n_gsm: fix deadlock and link starvation in outgoing data path | expand

Commit Message

D. Starke July 1, 2022, 12:23 p.m. UTC 
From: Daniel Starke <daniel.starke@siemens.com>

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>
---
 drivers/tty/n_gsm.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

Merged v4 into the tty-testing branch. No other changes applied.

Link: https://lore.kernel.org/all/20220701061652.39604-8-daniel.starke@siemens.com/
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Patch

diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index 79869f2b570c..ba399a660573 100644
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -2497,6 +2497,10 @@  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);
@@ -2513,9 +2517,6 @@  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;