Vyper vulnerable to OOB DynArray access when array is on both LHS and RHS of an assignment

@@ -1748,3 +1748,95 @@ def foo(i: uint256) -> {return_type}:
     return MY_CONSTANT[i]
     """
     assert_compile_failed(lambda: get_contract(code), TypeMismatch)
+
+
+dynarray_length_no_clobber_cases = [
+    # GHSA-3p37-3636-q8wv cases
+    """
+a: DynArray[uint256,3]
+
+@external
+def should_revert() -> DynArray[uint256,3]:
+    self.a = [1,2,3]
+    self.a = empty(DynArray[uint256,3])
+    self.a = [self.a[0], self.a[1], self.a[2]]
+
+    return self.a  # if bug: returns [1,2,3]
+    """,
+    """
+@external
+def should_revert() -> DynArray[uint256,3]:
+    self.a()
+    return self.b() # if bug: returns [1,2,3]
+
+@internal
+def a():
+    a: uint256 = 0
+    b: uint256 = 1
+    c: uint256 = 2
+    d: uint256 = 3
+
+@internal
+def b() -> DynArray[uint256,3]:
+    a: DynArray[uint256,3] = empty(DynArray[uint256,3])
+    a = [a[0],a[1],a[2]]
+    return a
+    """,
+    """
+a: DynArray[uint256,4]
+
+@external
+def should_revert() -> DynArray[uint256,4]:
+    self.a = [1,2,3]
+    self.a = empty(DynArray[uint256,4])
+    self.a = [4, self.a[0]]
+
+    return self.a  # if bug: return [4, 4]
+    """,
+    """
+@external
+def should_revert() -> DynArray[uint256,4]:
+    a: DynArray[uint256, 4] = [1,2,3]
+    a = []
+
+    a = [a.pop()]  # if bug: return [1]
+
+    return a
+    """,
+    """
+@external
+def should_revert():
+    c: DynArray[uint256, 1] = []
+    c.append(c[0])
+    """,
+    """
+@external
+def should_revert():
+    c: DynArray[uint256, 1] = [1]
+    c[0] = c.pop()
+    """,
+    """
+@external
+def should_revert():
+    c: DynArray[DynArray[uint256, 1], 2] = [[]]
+    c[0] = c.pop()
+    """,
+    """
+a: DynArray[String[65],2]
+
+@external
+def should_revert() -> DynArray[String[65], 2]:
+    self.a = ["hello", "world"]
+    self.a = []
+    self.a = [self.a[0], self.a[1]]
+
+    return self.a  # if bug: return ["hello", "world"]
+    """,
+]
+
+
+@pytest.mark.parametrize("code", dynarray_length_no_clobber_cases)
+def test_dynarray_length_no_clobber(get_contract, assert_tx_failed, code):
+    # check that length is not clobbered before dynarray data copy happens
+    c = get_contract(code)
+    assert_tx_failed(lambda: c.should_revert())

@@ -117,13 +117,15 @@ def make_byte_array_copier(dst, src):
             max_bytes = src.typ.maxlen
 
             ret = ["seq"]
+
+            dst_ = bytes_data_ptr(dst)
+            src_ = bytes_data_ptr(src)
+
+            ret.append(copy_bytes(dst_, src_, len_, max_bytes))
+
             # store length
             ret.append(STORE(dst, len_))
 
-            dst = bytes_data_ptr(dst)
-            src = bytes_data_ptr(src)
-
-            ret.append(copy_bytes(dst, src, len_, max_bytes))
             return b1.resolve(b2.resolve(ret))
 
 
@@ -148,25 +150,34 @@ def _dynarray_make_setter(dst, src):
     if src.value == "~empty":
         return IRnode.from_list(STORE(dst, 0))
 
+    # copy contents of src dynarray to dst.
+    # note that in case src and dst refer to the same dynarray,
+    # in order for get_element_ptr oob checks on the src dynarray
+    # to work, we need to wait until after the data is copied
+    # before we clobber the length word.
+
     if src.value == "multi":
         ret = ["seq"]
         # handle literals
 
-        # write the length word
-        store_length = STORE(dst, len(src.args))
-        ann = None
-        if src.annotation is not None:
-            ann = f"len({src.annotation})"
-        store_length = IRnode.from_list(store_length, annotation=ann)
-        ret.append(store_length)
-
+        # copy each item
         n_items = len(src.args)
+
         for i in range(n_items):
             k = IRnode.from_list(i, typ=UINT256_T)
             dst_i = get_element_ptr(dst, k, array_bounds_check=False)
             src_i = get_element_ptr(src, k, array_bounds_check=False)
             ret.append(make_setter(dst_i, src_i))
 
+        # write the length word after data is copied
+        store_length = STORE(dst, n_items)
+        ann = None
+        if src.annotation is not None:
+            ann = f"len({src.annotation})"
+        store_length = IRnode.from_list(store_length, annotation=ann)
+
+        ret.append(store_length)
+
         return ret
 
     with src.cache_when_complex("darray_src") as (b1, src):
@@ -190,8 +201,6 @@ def _dynarray_make_setter(dst, src):
         with get_dyn_array_count(src).cache_when_complex("darray_count") as (b2, count):
             ret = ["seq"]
 
-            ret.append(STORE(dst, count))
-
             if should_loop:
                 i = IRnode.from_list(_freshname("copy_darray_ix"), typ=UINT256_T)
 
@@ -213,6 +222,9 @@ def _dynarray_make_setter(dst, src):
                 dst_ = dynarray_data_ptr(dst)
                 ret.append(copy_bytes(dst_, src_, n_bytes, max_bytes))
 
+            # write the length word after data is copied
+            ret.append(STORE(dst, count))
+
             return b1.resolve(b2.resolve(ret))
 
 
@@ -336,12 +348,14 @@ def append_dyn_array(darray_node, elem_node):
         with len_.cache_when_complex("old_darray_len") as (b2, len_):
             assertion = ["assert", ["lt", len_, darray_node.typ.count]]
             ret.append(IRnode.from_list(assertion, error_msg=f"{darray_node.typ} bounds check"))
-            ret.append(STORE(darray_node, ["add", len_, 1]))
             # NOTE: typechecks elem_node
             # NOTE skip array bounds check bc we already asserted len two lines up
             ret.append(
                 make_setter(get_element_ptr(darray_node, len_, array_bounds_check=False), elem_node)
             )
+
+            # store new length
+            ret.append(STORE(darray_node, ["add", len_, 1]))
             return IRnode.from_list(b1.resolve(b2.resolve(ret)))
 
 
@@ -354,6 +368,7 @@ def pop_dyn_array(darray_node, return_popped_item):
         new_len = IRnode.from_list(["sub", old_len, 1], typ=UINT256_T)
 
         with new_len.cache_when_complex("new_len") as (b2, new_len):
+            # store new length
             ret.append(STORE(darray_node, new_len))
 
             # NOTE skip array bounds check bc we already asserted len two lines up
@@ -364,6 +379,7 @@ def pop_dyn_array(darray_node, return_popped_item):
                 location = popped_item.location
             else:
                 typ, location = None, None
+
             return IRnode.from_list(b1.resolve(b2.resolve(ret)), typ=typ, location=location)