From 3dfa23b9eff4315817c1acf59711b8414347de31 Mon Sep 17 00:00:00 2001
From: Kevin Wolf <kwolf@redhat.com>
Date: Tue, 23 Jun 2020 19:55:34 +0200
Subject: [PATCH] vvfat: Fix array_remove_slice()

array_remove_slice() calls array_roll() with array->next - 1 as the
destination index. This is only correct for count == 1, otherwise we're
writing past the end of the array. array->next - count would be correct.

However, this is the only place ever calling array_roll(), so this
rather complicated operation isn't even necessary.

Fix the problem and simplify the code by replacing it with a single
memmove() call. array_roll() can now be removed.

Reported-by: Nathan Huckleberry <nhuck15@gmail.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20200623175534.38286-3-kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 block/vvfat.c | 42 +++++-------------------------------------
 1 file changed, 5 insertions(+), 37 deletions(-)

diff --git a/block/vvfat.c b/block/vvfat.c
index 62230542e5..2eb8cbb19f 100644
--- a/block/vvfat.c
+++ b/block/vvfat.c
@@ -140,48 +140,16 @@ static inline void* array_insert(array_t* array,unsigned int index,unsigned int
     return array->pointer+index*array->item_size;
 }
 
-/* this performs a "roll", so that the element which was at index_from becomes
- * index_to, but the order of all other elements is preserved. */
-static inline int array_roll(array_t* array,int index_to,int index_from,int count)
-{
-    char* buf;
-    char* from;
-    char* to;
-    int is;
-
-    if(!array ||
-            index_to<0 || index_to>=array->next ||
-            index_from<0 || index_from>=array->next)
-        return -1;
-
-    if(index_to==index_from)
-        return 0;
-
-    is=array->item_size;
-    from=array->pointer+index_from*is;
-    to=array->pointer+index_to*is;
-    buf=g_malloc(is*count);
-    memcpy(buf,from,is*count);
-
-    if(index_to<index_from)
-        memmove(to+is*count,to,from-to);
-    else
-        memmove(from,from+is*count,to-from);
-
-    memcpy(to,buf,is*count);
-
-    g_free(buf);
-
-    return 0;
-}
-
 static inline int array_remove_slice(array_t* array,int index, int count)
 {
     assert(index >=0);
     assert(count > 0);
     assert(index + count <= array->next);
-    if(array_roll(array,array->next-1,index,count))
-        return -1;
+
+    memmove(array->pointer + index * array->item_size,
+            array->pointer + (index + count) * array->item_size,
+            (array->next - index - count) * array->item_size);
+
     array->next -= count;
     return 0;
 }