firewire: cdev: fix race in iso context creation

Protect the client's iso context pointer against a race that can happen
when more than one creation call is executed at the same time.

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>

1 files changed, 8 insertions, 5 deletions

diff --git a/drivers/firewire/core-cdev.c b/drivers/firewire/core-cdev.c
index 4e0478d70d4d..ce8cb6fcbbcd 100644
--- a/drivers/firewire/core-cdev.c
+++ b/drivers/firewire/core-cdev.c
@@ -864,10 +864,6 @@ static int ioctl_create_iso_context(struct client *client, union ioctl_arg *arg)
         struct fw_cdev_create_iso_context *a = &arg->create_iso_context;
         struct fw_iso_context *context;
 
-        /* We only support one context at this time. */
-        if (client->iso_context != NULL)
-                return -EBUSY;
-
         if (a->channel > 63)
                 return -EINVAL;
 
@@ -892,10 +888,17 @@ static int ioctl_create_iso_context(struct client *client, union ioctl_arg *arg)
         if (IS_ERR(context))
                 return PTR_ERR(context);
 
+        /* We only support one context at this time. */
+        spin_lock_irq(&client->lock);
+        if (client->iso_context != NULL) {
+                spin_unlock_irq(&client->lock);
+                fw_iso_context_destroy(context);
+                return -EBUSY;
+        }
         client->iso_closure = a->closure;
         client->iso_context = context;
+        spin_unlock_irq(&client->lock);
 
-        /* We only support one context at this time. */
         a->handle = 0;
 
         return 0;