pinctrl: avoid unsafe code pattern in find_pinctrl()

commit c153a4edff6ab01370fcac8e46f9c89cca1060c2 upstream.

The code in find_pinctrl() takes a mutex and traverses a list of pinctrl
structures. Later the caller bumps up reference count on the found
structure. Such pattern is not safe as pinctrl that was found may get
deleted before the caller gets around to increasing the reference count.

Fix this by taking the reference count in find_pinctrl(), while it still
holds the mutex.

Cc: stable@vger.kernel.org
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Link: https://lore.kernel.org/r/ZQs1RgTKg6VJqmPs@google.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/pinctrl/core.c b/drivers/pinctrl/core.c
index 9e57f4c62e609c3d3db203cfd475bee0196ba793..27e41873c04ff021487ee18a6ec6a9aec06032ee 100644 (file)
--- a/drivers/pinctrl/core.c
+++ b/drivers/pinctrl/core.c
@@ -1007,17 +1007,20 @@ static int add_setting(struct pinctrl *p, struct pinctrl_dev *pctldev,
 
 static struct pinctrl *find_pinctrl(struct device *dev)
 {
-       struct pinctrl *p;
+       struct pinctrl *entry, *p = NULL;
 
        mutex_lock(&pinctrl_list_mutex);
-       list_for_each_entry(p, &pinctrl_list, node)
-               if (p->dev == dev) {
-                       mutex_unlock(&pinctrl_list_mutex);
-                       return p;
+
+       list_for_each_entry(entry, &pinctrl_list, node) {
+               if (entry->dev == dev) {
+                       p = entry;
+                       kref_get(&p->users);
+                       break;
                }
+       }
 
        mutex_unlock(&pinctrl_list_mutex);
-       return NULL;
+       return p;
 }
 
 static void pinctrl_free(struct pinctrl *p, bool inlist);
@@ -1126,7 +1129,6 @@ struct pinctrl *pinctrl_get(struct device *dev)
        p = find_pinctrl(dev);
        if (p) {
                dev_dbg(dev, "obtain a copy of previously claimed pinctrl\n");
-               kref_get(&p->users);
                return p;
        }