pps: make idr lock a mutex and protect idr_pre_get

Now pps_idr_lock is never used in interrupt context so we can replace
spin_lock_irq/spin_unlock_irq with plain spin_lock/spin_unlock. But
there is also a potential race condition when someone can steal an id
which was allocated by idr_pre_get before it is used. So convert spin
lock to mutex and protect the whole id generation process.

Signed-off-by: Alexander Gordeev <lasaine@lvk.cs.msu.su>
Cc: Rodolfo Giometti <giometti@linux.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 11 insertions, 8 deletions

diff --git a/drivers/pps/pps.c b/drivers/pps/pps.c
index 79b445578132..9e15cf1da946 100644
--- a/drivers/pps/pps.c
+++ b/drivers/pps/pps.c
@@ -27,6 +27,7 @@
 #include <linux/sched.h>
 #include <linux/uaccess.h>
 #include <linux/idr.h>
+#include <linux/mutex.h>
 #include <linux/cdev.h>
 #include <linux/poll.h>
 #include <linux/pps_kernel.h>
@@ -39,7 +40,7 @@
 static dev_t pps_devt;
 static struct class *pps_class;
 
-static DEFINE_SPINLOCK(pps_idr_lock);
+static DEFINE_MUTEX(pps_idr_lock);
 static DEFINE_IDR(pps_idr);
 
 /*
@@ -239,9 +240,9 @@ static void pps_device_destruct(struct device *dev)
 
         /* release id here to protect others from using it while it's
          * still in use */
-        spin_lock_irq(&pps_idr_lock);
+        mutex_lock(&pps_idr_lock);
         idr_remove(&pps_idr, pps->id);
-        spin_unlock_irq(&pps_idr_lock);
+        mutex_unlock(&pps_idr_lock);
 
         kfree(dev);
         kfree(pps);
@@ -252,17 +253,19 @@ int pps_register_cdev(struct pps_device *pps)
         int err;
         dev_t devt;
 
+        mutex_lock(&pps_idr_lock);
         /* Get new ID for the new PPS source */
-        if (idr_pre_get(&pps_idr, GFP_KERNEL) == 0)
+        if (idr_pre_get(&pps_idr, GFP_KERNEL) == 0) {
+                mutex_unlock(&pps_idr_lock);
                 return -ENOMEM;
+        }
 
         /* Now really allocate the PPS source.
          * After idr_get_new() calling the new source will be freely available
          * into the kernel.
          */
-        spin_lock_irq(&pps_idr_lock);
         err = idr_get_new(&pps_idr, pps, &pps->id);
-        spin_unlock_irq(&pps_idr_lock);
+        mutex_unlock(&pps_idr_lock);
 
         if (err < 0)
                 return err;
@@ -302,9 +305,9 @@ del_cdev:
         cdev_del(&pps->cdev);
 
 free_idr:
-        spin_lock_irq(&pps_idr_lock);
+        mutex_lock(&pps_idr_lock);
         idr_remove(&pps_idr, pps->id);
-        spin_unlock_irq(&pps_idr_lock);
+        mutex_unlock(&pps_idr_lock);
 
         return err;
 }