staging: android: ashmem: Avoid range_alloc() allocation with ashmem_mutex held.

ashmem_pin() is calling range_shrink() without checking whether
range_alloc() succeeded. Also, doing memory allocation with ashmem_mutex
held should be avoided because ashmem_shrink_scan() tries to hold it.

Therefore, move memory allocation for range_alloc() to ashmem_pin_unpin()
and make range_alloc() not to fail.

This patch is mostly meant for backporting purpose for fuzz testing on
stable/distributor kernels, for there is a plan to remove this code in
near future.
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: stable@vger.kernel.org
Reviewed-by: Joel Fernandes <joel@joelfernandes.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/android/ashmem.c

@@ -172,19 +172,15 @@ static inline void lru_del(struct ashmem_range *range)
  * @end:	   The ending page (inclusive)
  *
  * This function is protected by ashmem_mutex.
- *
- * Return: 0 if successful, or -ENOMEM if there is an error
  */
-static int range_alloc(struct ashmem_area *asma,
+static void range_alloc(struct ashmem_area *asma,
 			struct ashmem_range *prev_range, unsigned int purged,
-		       size_t start, size_t end)
+			size_t start, size_t end,
+			struct ashmem_range **new_range)
 {
-	struct ashmem_range *range;
-
-	range = kmem_cache_zalloc(ashmem_range_cachep, GFP_KERNEL);
-	if (!range)
-		return -ENOMEM;
+	struct ashmem_range *range = *new_range;
 
+	*new_range = NULL;
 	range->asma = asma;
 	range->pgstart = start;
 	range->pgend = end;
@@ -194,8 +190,6 @@ static int range_alloc(struct ashmem_area *asma,
 
 	if (range_on_lru(range))
 		lru_add(range);
-
-	return 0;
 }
 
 /**
@@ -597,7 +591,8 @@ static int get_name(struct ashmem_area *asma, void __user *name)
  *
  * Caller must hold ashmem_mutex.
  */
-static int ashmem_pin(struct ashmem_area *asma, size_t pgstart, size_t pgend)
+static int ashmem_pin(struct ashmem_area *asma, size_t pgstart, size_t pgend,
+		      struct ashmem_range **new_range)
 {
 	struct ashmem_range *range, *next;
 	int ret = ASHMEM_NOT_PURGED;
@@ -650,7 +645,7 @@ static int ashmem_pin(struct ashmem_area *asma, size_t pgstart, size_t pgend)
 			 * second half and adjust the first chunk's endpoint.
 			 */
 			range_alloc(asma, range, range->purged,
-				    pgend + 1, range->pgend);
+				    pgend + 1, range->pgend, new_range);
 			range_shrink(range, range->pgstart, pgstart - 1);
 			break;
 		}
@@ -664,7 +659,8 @@ static int ashmem_pin(struct ashmem_area *asma, size_t pgstart, size_t pgend)
  *
  * Caller must hold ashmem_mutex.
  */
-static int ashmem_unpin(struct ashmem_area *asma, size_t pgstart, size_t pgend)
+static int ashmem_unpin(struct ashmem_area *asma, size_t pgstart, size_t pgend,
+			struct ashmem_range **new_range)
 {
 	struct ashmem_range *range, *next;
 	unsigned int purged = ASHMEM_NOT_PURGED;
@@ -690,7 +686,8 @@ static int ashmem_unpin(struct ashmem_area *asma, size_t pgstart, size_t pgend)
 		}
 	}
 
-	return range_alloc(asma, range, purged, pgstart, pgend);
+	range_alloc(asma, range, purged, pgstart, pgend, new_range);
+	return 0;
 }
 
 /*
@@ -723,10 +720,17 @@ static int ashmem_pin_unpin(struct ashmem_area *asma, unsigned long cmd,
 	struct ashmem_pin pin;
 	size_t pgstart, pgend;
 	int ret = -EINVAL;
+	struct ashmem_range *range = NULL;
 
 	if (copy_from_user(&pin, p, sizeof(pin)))
 		return -EFAULT;
 
+	if (cmd == ASHMEM_PIN || cmd == ASHMEM_UNPIN) {
+		range = kmem_cache_zalloc(ashmem_range_cachep, GFP_KERNEL);
+		if (!range)
+			return -ENOMEM;
+	}
+
 	mutex_lock(&ashmem_mutex);
 	wait_event(ashmem_shrink_wait, !atomic_read(&ashmem_shrink_inflight));
 
@@ -751,10 +755,10 @@ static int ashmem_pin_unpin(struct ashmem_area *asma, unsigned long cmd,
 
 	switch (cmd) {
 	case ASHMEM_PIN:
-		ret = ashmem_pin(asma, pgstart, pgend);
+		ret = ashmem_pin(asma, pgstart, pgend, &range);
 		break;
 	case ASHMEM_UNPIN:
-		ret = ashmem_unpin(asma, pgstart, pgend);
+		ret = ashmem_unpin(asma, pgstart, pgend, &range);
 		break;
 	case ASHMEM_GET_PIN_STATUS:
 		ret = ashmem_get_pin_status(asma, pgstart, pgend);
@@ -763,6 +767,8 @@ static int ashmem_pin_unpin(struct ashmem_area *asma, unsigned long cmd,
 
 out_unlock:
 	mutex_unlock(&ashmem_mutex);
+	if (range)
+		kmem_cache_free(ashmem_range_cachep, range);
 
 	return ret;
 }