HID: core: replace the collection tree pointers with indices

Previously, the pointer to the parent collection was stored. If a device
exceeds 16 collections (HID_DEFAULT_NUM_COLLECTIONS), the array to store
the collections is reallocated, the pointer to the parent collection becomes
invalid.

Replace the pointers with an index-based lookup into the collections array.

Fixes: c53431eb696f3c ("HID: core: store the collections as a basic tree")
Reported-by: Pandruvada, Srinivas <srinivas.pandruvada@intel.com>
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Tested-by: Kyle Pelton <kyle.d.pelton@linux.intel.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

2 files changed, 23 insertions, 13 deletions

diff --git a/drivers/hid/hid-core.c b/drivers/hid/hid-core.c
index f41d5fe51abe..f9093dedf647 100644
--- a/drivers/hid/hid-core.c
+++ b/drivers/hid/hid-core.c
@@ -125,6 +125,7 @@ static int open_collection(struct hid_parser *parser, unsigned type)
 {
         struct hid_collection *collection;
         unsigned usage;
+        int collection_index;
 
         usage = parser->local.usage[0];
 
@@ -167,13 +168,13 @@ static int open_collection(struct hid_parser *parser, unsigned type)
         parser->collection_stack[parser->collection_stack_ptr++] =
                 parser->device->maxcollection;
 
-        collection = parser->device->collection +
-                parser->device->maxcollection++;
+        collection_index = parser->device->maxcollection++;
+        collection = parser->device->collection + collection_index;
         collection->type = type;
         collection->usage = usage;
         collection->level = parser->collection_stack_ptr - 1;
-        collection->parent = parser->active_collection;
-        parser->active_collection = collection;
+        collection->parent_idx = parser->active_collection_idx;
+        parser->active_collection_idx = collection_index;
 
         if (type == HID_COLLECTION_APPLICATION)
                 parser->device->maxapplication++;
@@ -192,8 +193,13 @@ static int close_collection(struct hid_parser *parser)
                 return -EINVAL;
         }
         parser->collection_stack_ptr--;
-        if (parser->active_collection)
-                parser->active_collection = parser->active_collection->parent;
+        if (parser->active_collection_idx != -1) {
+                struct hid_device *device = parser->device;
+                struct hid_collection *c;
+
+                c = &device->collection[parser->active_collection_idx];
+                parser->active_collection_idx = c->parent_idx;
+        }
         return 0;
 }
 
@@ -819,6 +825,7 @@ static int hid_scan_report(struct hid_device *hid)
                 return -ENOMEM;
 
         parser->device = hid;
+        parser->active_collection_idx = -1;
         hid->group = HID_GROUP_GENERIC;
 
         /*
@@ -1006,10 +1013,12 @@ static void hid_apply_multiplier_to_field(struct hid_device *hid,
                 usage = &field->usage[i];
 
                 collection = &hid->collection[usage->collection_index];
-                while (collection && collection != multiplier_collection)
-                        collection = collection->parent;
+                while (collection->parent_idx != -1 &&
+                       collection != multiplier_collection)
+                        collection = &hid->collection[collection->parent_idx];
 
-                if (collection || multiplier_collection == NULL)
+                if (collection->parent_idx != -1 ||
+                    multiplier_collection == NULL)
                         usage->resolution_multiplier = effective_multiplier;
 
         }
@@ -1044,9 +1053,9 @@ static void hid_apply_multiplier(struct hid_device *hid,
          * applicable fields later.
          */
         multiplier_collection = &hid->collection[multiplier->usage->collection_index];
-        while (multiplier_collection &&
+        while (multiplier_collection->parent_idx != -1 &&
                multiplier_collection->type != HID_COLLECTION_LOGICAL)
-                multiplier_collection = multiplier_collection->parent;
+                multiplier_collection = &hid->collection[multiplier_collection->parent_idx];
 
         effective_multiplier = hid_calculate_multiplier(hid, multiplier);
 
@@ -1170,6 +1179,7 @@ int hid_open_report(struct hid_device *device)
         }
 
         parser->device = device;
+        parser->active_collection_idx = -1;
 
         end = start + size;
 
diff --git a/include/linux/hid.h b/include/linux/hid.h
index d99287327ef2..992bbb7196df 100644
--- a/include/linux/hid.h
+++ b/include/linux/hid.h
@@ -430,7 +430,7 @@ struct hid_local {
  */
 
 struct hid_collection {
-        struct hid_collection *parent;
+        int parent_idx; /* device->collection */
         unsigned type;
         unsigned usage;
         unsigned level;
@@ -658,7 +658,7 @@ struct hid_parser {
         unsigned int         *collection_stack;
         unsigned int          collection_stack_ptr;
         unsigned int          collection_stack_size;
-        struct hid_collection *active_collection;
+        int                   active_collection_idx; /* device->collection */
         struct hid_device    *device;
         unsigned int          scan_flags;
 };