uber · isaacbrodsky · Sep 8, 2022 · Sep 6, 2022 · Sep 6, 2022
diff --git a/src/apps/fuzzers/fuzzerGridDisk.c b/src/apps/fuzzers/fuzzerGridDisk.c
@@ -26,6 +26,8 @@ typedef struct {
     int64_t k;
 } inputArgs;
 
+// This is limited to avoid timeouts due to the runtime of gridDisk growing with
+// k
 const int64_t MAX_GRID_DISK_SIZE = 0x1000000;
 
 int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {

diff --git a/src/apps/testapps/testDirectedEdge.c b/src/apps/testapps/testDirectedEdge.c
@@ -93,6 +93,34 @@ SUITE(directedEdge) {
         t_assert(isNeighbor, "hexagons in a ring are neighbors");
     }
 
+    TEST(areNeighborCells_invalid) {
+        H3Index origin;
+        setH3Index(&origin, 5, 0, CENTER_DIGIT);
+        H3Index dest = origin;
+        H3_SET_INDEX_DIGIT(origin, 5, INVALID_DIGIT);
+        H3_SET_INDEX_DIGIT(dest, 5, JK_AXES_DIGIT);
+        int out;
+
+        t_assert(
+            H3_EXPORT(areNeighborCells)(origin, dest, &out) == E_CELL_INVALID,
+            "Invalid index digit origin is rejected");
+
+        setH3Index(&origin, 5, 4, CENTER_DIGIT);
+        dest = origin;
+        H3_SET_INDEX_DIGIT(origin, 5, K_AXES_DIGIT);
+        H3_SET_INDEX_DIGIT(dest, 5, IK_AXES_DIGIT);
+        t_assert(
+            H3_EXPORT(areNeighborCells)(origin, dest, &out) == E_CELL_INVALID,
+            "Invalid k subsequence origin is rejected");
+        H3_SET_INDEX_DIGIT(origin, 5, IK_AXES_DIGIT);
+        H3_SET_INDEX_DIGIT(dest, 5, K_AXES_DIGIT);
+        t_assert(
+            H3_EXPORT(areNeighborCells)(origin, dest, &out) == E_CELL_INVALID,
+            "Invalid k subsequence destination is rejected");
+        // Can't test origin and dest both having K_AXES_DIGIT as this will be
+        // rejected as the same cell.
+    }
+
     TEST(cellsToDirectedEdgeAndFriends) {
         H3Index sf;
         t_assertSuccess(H3_EXPORT(latLngToCell)(&sfGeo, 9, &sf));

diff --git a/src/h3lib/lib/directedEdge.c b/src/h3lib/lib/directedEdge.c
@@ -75,6 +75,20 @@ H3Error H3_EXPORT(areNeighborCells)(H3Index origin, H3Index destination,
                 *out = 1;
                 return E_SUCCESS;
             }
+            if (originResDigit >= INVALID_DIGIT) {
+                // Prevent indexing off the end of the array below
+                return E_CELL_INVALID;
+            }
+            if ((originResDigit == K_AXES_DIGIT ||
+                 destinationResDigit == K_AXES_DIGIT) &&
+                H3_EXPORT(isPentagon)(originParent)) {
+                // If these are invalid cells, fail rather than incorrectly
+                // reporting neighbors. For pentagon cells that are actually
+                // neighbors across the deleted subsequence, they will fail the
+                // optimized check below, but they will be accepted by the
+                // gridDisk check below that.
+                return E_CELL_INVALID;
+            }
             // These sets are the relevant neighbors in the clockwise
             // and counter-clockwise
             const Direction neighborSetClockwise[] = {