[PATCH v3] char: pcmcia: synclink_cs: Fix use-after-free in mgslpc_ops

Hyunwoo Kim
2022-09-16T13:48:04Z

A race condition may occur if the user physically removes
the pcmcia device while calling ioctl() for this tty device node.

This is a race condition between the mgslpc_ioctl() function and
the mgslpc_detach() function, which may eventually result in UAF.

So, add a refcount check to mgslpc_detach() to free the structure
after the tty device node is close()d.

Signed-off-by: Hyunwoo Kim <imv4bel@gmail.com>
---
drivers/char/pcmcia/synclink_cs.c | 44 ++++++++++++++++++++++++++++---
1 file changed, 40 insertions(+), 4 deletions(-)

diff --git a/drivers/char/pcmcia/synclink_cs.c b/drivers/char/pcmcia/synclink_cs.c
index 8fc49b038372..c991acfbc34d 100644
--- a/drivers/char/pcmcia/synclink_cs.c
+++ b/drivers/char/pcmcia/synclink_cs.c
@@ -216,7 +216,9 @@ typedef struct _mgslpc_info {

/* PCMCIA support */
struct pcmcia_device *p_dev;
- int stop;
+ int stop;
+ int removed;
+ struct kref refcnt;

/* SPPP/Cisco HDLC device parts */
int netcount;
@@ -228,6 +230,8 @@ typedef struct _mgslpc_info {

} MGSLPC_INFO;

+static DEFINE_MUTEX(remove_mutex);
+
#define MGSLPC_MAGIC 0x5402

/*
@@ -468,10 +472,21 @@ static void mgslpc_wait_until_sent(struct tty_struct *tty, int timeout);

/* PCMCIA prototypes */

+static void mgslpc_delete(struct kref *kref);
static int mgslpc_config(struct pcmcia_device *link);
static void mgslpc_release(u_long arg);
static void mgslpc_detach(struct pcmcia_device *p_dev);

+static void mgslpc_delete(struct kref *kref)
+{
+ MGSLPC_INFO *info = container_of(kref, MGSLPC_INFO, refcnt);
+ struct pcmcia_device *link = info->p_dev;
+
+ mgslpc_release((u_long)link);
+
+ mgslpc_remove_device(info);
+}
+
/*
* 1st function defined in .text section. Calling this function in
* init_module() followed by a breakpoint allows a remote debugger
@@ -534,6 +549,7 @@ static int mgslpc_probe(struct pcmcia_device *link)
init_waitqueue_head(&info->event_wait_q);
spin_lock_init(&info->lock);
spin_lock_init(&info->netlock);
+ kref_init(&info->refcnt);
memcpy(&info->params,&default_params,sizeof(MGSL_PARAMS));
info->idle_mode = HDLC_TXIDLE_FLAGS;
info->imra_value = 0xffff;
@@ -620,13 +636,17 @@ static void mgslpc_release(u_long arg)

static void mgslpc_detach(struct pcmcia_device *link)
{
+ MGSLPC_INFO *info = link->priv;
+
+ mutex_lock(&remove_mutex);
if (debug_level >= DEBUG_LEVEL_INFO)
printk("mgslpc_detach(0x%p)\n", link);

- ((MGSLPC_INFO *)link->priv)->stop = 1;
- mgslpc_release((u_long)link);
+ info->stop = 1;

- mgslpc_remove_device((MGSLPC_INFO *)link->priv);
+ kref_put(&info->refcnt, mgslpc_delete);
+ info->removed = 1;
+ mutex_unlock(&remove_mutex);
}

static int mgslpc_suspend(struct pcmcia_device *link)
@@ -2341,10 +2361,13 @@ static void mgslpc_close(struct tty_struct *tty, struct file * filp)

tty_port_close_end(port, tty);
tty_port_tty_set(port, NULL);
+
cleanup:
if (debug_level >= DEBUG_LEVEL_INFO)
printk("%s(%d):mgslpc_close(%s) exit, count=%d\n", __FILE__, __LINE__,
tty->driver->name, port->count);
+
+ kref_put(&info->refcnt, mgslpc_delete);
}

/* Wait until the transmitter is empty.
@@ -2465,6 +2488,7 @@ static int mgslpc_open(struct tty_struct *tty, struct file * filp)
int retval, line;
unsigned long flags;

+
/* verify range of specified line number */
line = tty->index;
if (line >= mgslpc_device_count) {
@@ -2480,6 +2504,13 @@ static int mgslpc_open(struct tty_struct *tty, struct file * filp)
if (mgslpc_paranoia_check(info, tty->name, "mgslpc_open"))
return -ENODEV;

+ mutex_lock(&remove_mutex);
+
+ if (info->removed == 1) {
+ retval = -ENODEV;
+ goto cleanup;
+ }
+
port = &info->port;
tty->driver_data = info;
tty_port_tty_set(port, tty);
@@ -2517,9 +2548,14 @@ static int mgslpc_open(struct tty_struct *tty, struct file * filp)
if (debug_level >= DEBUG_LEVEL_INFO)
printk("%s(%d):mgslpc_open(%s) success\n",
__FILE__, __LINE__, info->device_name);
+
+ kref_get(&info->refcnt);
retval = 0;
+ mutex_unlock(&remove_mutex);

+ return retval;
cleanup:
+ mutex_unlock(&remove_mutex);
return retval;
}

--
2.25.1