maple_tree: fix allocation in mas_sparse_area()

In the case of reverse allocation, mas->index and mas->last do not point
to the correct allocation range, which will cause users to get incorrect
allocation results, so fix it.  If the user does not use it in a specific
way, this bug will not be triggered.

This is a bug, but only VMA uses it now, the way VMA is used now will
not trigger it.  There is a possibility that a user will trigger it in
the future.

Also re-check whether the size is still satisfied after the lower bound
was increased, which is a corner case and is incorrect in previous
versions.

Link: https://lkml.kernel.org/r/20230419093625.99201-1-zhangpeng.00@bytedance.com
Fixes: 54a611b60590 ("Maple Tree: add new data structure")
Signed-off-by: Peng Zhang <zhangpeng.00@bytedance.com>
Cc: Liam R. Howlett <Liam.Howlett@Oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/lib/maple_tree.c b/lib/maple_tree.c
index 9172bce..110a364 100644 (file)
--- a/lib/maple_tree.c
+++ b/lib/maple_tree.c
@@ -5250,25 +5250,28 @@ static inline void mas_fill_gap(struct ma_state *mas, void *entry,
  * @size: The size of the gap
  * @fwd: Searching forward or back
  */
-static inline void mas_sparse_area(struct ma_state *mas, unsigned long min,
+static inline int mas_sparse_area(struct ma_state *mas, unsigned long min,
                                unsigned long max, unsigned long size, bool fwd)
 {
-       unsigned long start = 0;
-
-       if (!unlikely(mas_is_none(mas)))
-               start++;
+       if (!unlikely(mas_is_none(mas)) && min == 0) {
+               min++;
+               /*
+                * At this time, min is increased, we need to recheck whether
+                * the size is satisfied.
+                */
+               if (min > max || max - min + 1 < size)
+                       return -EBUSY;
+       }
        /* mas_is_ptr */
 
-       if (start < min)
-               start = min;
-
        if (fwd) {
-               mas->index = start;
-               mas->last = start + size - 1;
-               return;
+               mas->index = min;
+               mas->last = min + size - 1;
+       } else {
+               mas->last = max;
+               mas->index = max - size + 1;
        }
-
-       mas->index = max;
+       return 0;
 }
 
 /*
@@ -5297,10 +5300,8 @@ int mas_empty_area(struct ma_state *mas, unsigned long min,
                return -EBUSY;
 
        /* Empty set */
-       if (mas_is_none(mas) || mas_is_ptr(mas)) {
-               mas_sparse_area(mas, min, max, size, true);
-               return 0;
-       }
+       if (mas_is_none(mas) || mas_is_ptr(mas))
+               return mas_sparse_area(mas, min, max, size, true);
 
        /* The start of the window can only be within these values */
        mas->index = min;
@@ -5356,10 +5357,8 @@ int mas_empty_area_rev(struct ma_state *mas, unsigned long min,
        }
 
        /* Empty set. */
-       if (mas_is_none(mas) || mas_is_ptr(mas)) {
-               mas_sparse_area(mas, min, max, size, false);
-               return 0;
-       }
+       if (mas_is_none(mas) || mas_is_ptr(mas))
+               return mas_sparse_area(mas, min, max, size, false);
 
        /* The start of the window can only be within these values. */
        mas->index = min;