commit 97a9cd6748fb7d5ef99e7d68c346ecaba1318e94
author Chien-Yu Chen <cychen@google.com> Fri Aug 12 15:40:16 2016 -0700
committer Chien-Yu Chen <cychen@google.com> Tue Aug 16 13:03:39 2016 -0700
tree 4ad7088d0500c70e6f98bb778e77a8218ea70ee4
parent 30bf0cc133ecab46b7999ac791ebe95d0c51d746

Camera: Prevent data size overflow

Add a function to check overflow when calculating metadata
data size.

Bug: 30741779
Change-Id: I6405fe608567a4f4113674050f826f305ecae030

camera/src/camera_metadata.c

diff --git a/camera/src/camera_metadata.c b/camera/src/camera_metadata.c
index a413f66..3f435eb 100644
--- a/camera/src/camera_metadata.c
+++ b/camera/src/camera_metadata.c
@@ -22,9 +22,10 @@
 #include <stdlib.h>
 #include <errno.h>
 
-#define OK         0
-#define ERROR      1
-#define NOT_FOUND -ENOENT
+#define OK              0
+#define ERROR           1
+#define NOT_FOUND       -ENOENT
+#define SN_EVENT_LOG_ID 0x534e4554
 
 #define _Alignas(T) \
     ({struct _AlignasStruct { char c; T field; };       \
@@ -291,6 +292,38 @@
     return metadata;
 }
 
+// This method should be used when the camera metadata cannot be trusted. For example, when it's
+// read from Parcel.
+static int validate_and_calculate_camera_metadata_entry_data_size(size_t *data_size, uint8_t type,
+        size_t data_count) {
+    if (type >= NUM_TYPES) return ERROR;
+
+    // Check for overflow
+    if (data_count != 0 &&
+            camera_metadata_type_size[type] > (SIZE_MAX - DATA_ALIGNMENT + 1) / data_count) {
+        android_errorWriteLog(SN_EVENT_LOG_ID, "30741779");
+        return ERROR;
+    }
+
+    size_t data_bytes = data_count * camera_metadata_type_size[type];
+
+    if (data_size) {
+        *data_size = data_bytes <= 4 ? 0 : ALIGN_TO(data_bytes, DATA_ALIGNMENT);
+    }
+
+    return OK;
+}
+
+size_t calculate_camera_metadata_entry_data_size(uint8_t type,
+        size_t data_count) {
+    if (type >= NUM_TYPES) return 0;
+
+    size_t data_bytes = data_count *
+            camera_metadata_type_size[type];
+
+    return data_bytes <= 4 ? 0 : ALIGN_TO(data_bytes, DATA_ALIGNMENT);
+}
+
 int validate_camera_metadata_structure(const camera_metadata_t *metadata,
                                        const size_t *expected_size) {
 
@@ -400,9 +433,13 @@
             return ERROR;
         }
 
-        size_t data_size =
-                calculate_camera_metadata_entry_data_size(entry.type,
-                                                          entry.count);
+        size_t data_size;
+        if (validate_and_calculate_camera_metadata_entry_data_size(&data_size, entry.type,
+                entry.count) != OK) {
+            ALOGE("%s: Entry data size is invalid. type: %u count: %u", __FUNCTION__, entry.type,
+                    entry.count);
+            return ERROR;
+        }
 
         if (data_size != 0) {
             camera_metadata_data_t *data =
@@ -492,14 +529,6 @@
     return clone;
 }
 
-size_t calculate_camera_metadata_entry_data_size(uint8_t type,
-        size_t data_count) {
-    if (type >= NUM_TYPES) return 0;
-    size_t data_bytes = data_count *
-            camera_metadata_type_size[type];
-    return data_bytes <= 4 ? 0 : ALIGN_TO(data_bytes, DATA_ALIGNMENT);
-}
-
 static int add_camera_metadata_entry_raw(camera_metadata_t *dst,
         uint32_t tag,
         uint8_t  type,