From: Daniel Starke daniel.starke@siemens.com
commit 1ec92e9742774bf42614fceea3bf6b50c9409225 upstream.
The active mux instances are managed in the gsm_mux array and via mux_get() and mux_put() functions separately. This gives a very loose coupling between the actual instance and the gsm_mux array which manages it. It also results in unnecessary lockings which makes it prone to failures. And it creates a race condition if more than the maximum number of mux instances are requested while the user changes the parameters of an active instance. The user may loose ownership of the current mux instance in this case. Fix this by moving the gsm_mux array handling to the mux allocation and deallocation functions.
Fixes: e1eaea46bb40 ("tty: n_gsm line discipline") Cc: stable@vger.kernel.org Signed-off-by: Daniel Starke daniel.starke@siemens.com Link: https://lore.kernel.org/r/20220414094225.4527-3-daniel.starke@siemens.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/tty/n_gsm.c | 63 +++++++++++++++++++++++++++++++--------------------- 1 file changed, 38 insertions(+), 25 deletions(-)
--- a/drivers/tty/n_gsm.c +++ b/drivers/tty/n_gsm.c @@ -2136,18 +2136,6 @@ static void gsm_cleanup_mux(struct gsm_m /* Finish outstanding timers, making sure they are done */ del_timer_sync(&gsm->t2_timer);
- spin_lock(&gsm_mux_lock); - for (i = 0; i < MAX_MUX; i++) { - if (gsm_mux[i] == gsm) { - gsm_mux[i] = NULL; - break; - } - } - spin_unlock(&gsm_mux_lock); - /* open failed before registering => nothing to do */ - if (i == MAX_MUX) - return; - /* Free up any link layer users */ for (i = 0; i < NUM_DLCI; i++) if (gsm->dlci[i]) @@ -2171,7 +2159,6 @@ static void gsm_cleanup_mux(struct gsm_m static int gsm_activate_mux(struct gsm_mux *gsm) { struct gsm_dlci *dlci; - int i = 0;
timer_setup(&gsm->t2_timer, gsm_control_retransmit, 0); init_waitqueue_head(&gsm->event); @@ -2183,18 +2170,6 @@ static int gsm_activate_mux(struct gsm_m else gsm->receive = gsm1_receive;
- spin_lock(&gsm_mux_lock); - for (i = 0; i < MAX_MUX; i++) { - if (gsm_mux[i] == NULL) { - gsm->num = i; - gsm_mux[i] = gsm; - break; - } - } - spin_unlock(&gsm_mux_lock); - if (i == MAX_MUX) - return -EBUSY; - dlci = gsm_dlci_alloc(gsm, 0); if (dlci == NULL) return -ENOMEM; @@ -2210,6 +2185,15 @@ static int gsm_activate_mux(struct gsm_m */ static void gsm_free_mux(struct gsm_mux *gsm) { + int i; + + for (i = 0; i < MAX_MUX; i++) { + if (gsm == gsm_mux[i]) { + gsm_mux[i] = NULL; + break; + } + } + mutex_destroy(&gsm->mutex); kfree(gsm->txframe); kfree(gsm->buf); kfree(gsm); @@ -2229,12 +2213,20 @@ static void gsm_free_muxr(struct kref *r
static inline void mux_get(struct gsm_mux *gsm) { + unsigned long flags; + + spin_lock_irqsave(&gsm_mux_lock, flags); kref_get(&gsm->ref); + spin_unlock_irqrestore(&gsm_mux_lock, flags); }
static inline void mux_put(struct gsm_mux *gsm) { + unsigned long flags; + + spin_lock_irqsave(&gsm_mux_lock, flags); kref_put(&gsm->ref, gsm_free_muxr); + spin_unlock_irqrestore(&gsm_mux_lock, flags); }
static inline unsigned int mux_num_to_base(struct gsm_mux *gsm) @@ -2255,6 +2247,7 @@ static inline unsigned int mux_line_to_n
static struct gsm_mux *gsm_alloc_mux(void) { + int i; struct gsm_mux *gsm = kzalloc(sizeof(struct gsm_mux), GFP_KERNEL); if (gsm == NULL) return NULL; @@ -2284,6 +2277,26 @@ static struct gsm_mux *gsm_alloc_mux(voi gsm->mtu = 64; gsm->dead = true; /* Avoid early tty opens */
+ /* Store the instance to the mux array or abort if no space is + * available. + */ + spin_lock(&gsm_mux_lock); + for (i = 0; i < MAX_MUX; i++) { + if (!gsm_mux[i]) { + gsm_mux[i] = gsm; + gsm->num = i; + break; + } + } + spin_unlock(&gsm_mux_lock); + if (i == MAX_MUX) { + mutex_destroy(&gsm->mutex); + kfree(gsm->txframe); + kfree(gsm->buf); + kfree(gsm); + return NULL; + } + return gsm; }