From df63da98d8dc284b1c76cfe1b17fa0acbd6094d8 Mon Sep 17 00:00:00 2001
From: Christian Brabandt <cb@256bit.org>
Date: Thu, 23 Nov 2023 20:14:28 +0100
Subject: [PATCH] patch 9.0.2123: Problem with initializing the length of
 range() lists

Problem:  Problem with initializing the length of range() lists
Solution: Set length explicitly when it shouldn't contain any items

range() may cause a wrong calculation of list length, which may later
then cause a segfault in list_find().  This is usually not a problem,
because range_list_materialize() calculates the length, when it
materializes the list.

In addition, in list_find() when the length of the range was wrongly
initialized, it may seem to be valid, so the check for list index
out-of-bounds will not be true, because it is called before the list is
actually materialized. And so we may eventually try to access a null
pointer, causing a segfault.

So this patch does 3 things:

- In f_range(), when we know that the list should be empty, explicitly
  set the list->lv_len value to zero. This should happen, when
  start is larger than end (in case the stride is positive) or
  end is larger than start when the stride is negative.
  This should fix the underlying issue properly. However,

- as a safety measure, let's check that the requested index is not
  out of range one more time, after the list has been materialized
  and return NULL in case it suddenly is.

- add a few more tests to verify the behaviour.

fixes: #13557
closes: #13563

Co-authored-by: Tim Pope <tpope@github.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
---
 src/evalfunc.c                 | 5 ++++-
 src/list.c                     | 4 ++++
 src/testdir/test_functions.vim | 3 +++
 3 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/src/evalfunc.c b/src/evalfunc.c
index 7f7914eca7d91..fa27d0d274a64 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -8646,7 +8646,10 @@ f_range(typval_T *argvars, typval_T *rettv)
     list->lv_u.nonmat.lv_start = start;
     list->lv_u.nonmat.lv_end = end;
     list->lv_u.nonmat.lv_stride = stride;
-    list->lv_len = (end - start) / stride + 1;
+    if (stride > 0 ? end < start : end > start)
+	list->lv_len = 0;
+    else
+	list->lv_len = (end - start) / stride + 1;
 }
 
 /*
diff --git a/src/list.c b/src/list.c
index d1494c67d56e9..ce1ccaa1c045c 100644
--- a/src/list.c
+++ b/src/list.c
@@ -415,6 +415,10 @@ list_find(list_T *l, long n)
 
     CHECK_LIST_MATERIALIZE(l);
 
+    // range_list_materialize may reset l->lv_len
+    if (n >= l->lv_len)
+	return NULL;
+
     // When there is a cached index may start search from there.
     if (l->lv_u.mat.lv_idx_item != NULL)
     {
diff --git a/src/testdir/test_functions.vim b/src/testdir/test_functions.vim
index 49b688c25f347..0801d2b695b76 100644
--- a/src/testdir/test_functions.vim
+++ b/src/testdir/test_functions.vim
@@ -3052,6 +3052,9 @@ func Test_range()
   " get()
   call assert_equal(4, get(range(1, 10), 3))
   call assert_equal(-1, get(range(1, 10), 42, -1))
+  call assert_equal(0, get(range(1, 0, 2), 0))
+  call assert_equal(0, get(range(0, -1, 2), 0))
+  call assert_equal(0, get(range(-2, -1, -2), 0))
 
   " index()
   call assert_equal(1, index(range(1, 5), 2))