[PATCH] maple_tree: Fix mas_empty_area_rev() lower bound validation

[Liam Howlett]

mas_empty_area_rev() was not correctly validating the start of a gap
against the lower limit.  This could lead to the range starting lower
than the requested minimum.

Fix the issue by better validating a gap once one is found.

This commit also adds tests to the maple tree test suite for this issue
and tests the mas_empty_area() function for similar bound checking.

Cc: stable@xxxxxxxxxxxxxxx
BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=216911
Reported-by: amanieu@xxxxxxxxx
Fixes: 54a611b60590 ("Maple Tree: add new data structure")
Link: https://lore.kernel.org/linux-mm/0b9f5425-08d4-8013-aa4c-e620c3b10bb2@xxxxxxxxxxxxx/
Signed-off-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
---
 lib/maple_tree.c      | 17 ++++-----
 lib/test_maple_tree.c | 89 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 97 insertions(+), 9 deletions(-)

diff --git a/lib/maple_tree.c b/lib/maple_tree.c
index 26e2045d3cda..b990ccea454e 100644
--- a/lib/maple_tree.c
+++ b/lib/maple_tree.c
@@ -4887,7 +4887,7 @@ static bool mas_rev_awalk(struct ma_state *mas, unsigned long size)
 	unsigned long *pivots, *gaps;
 	void __rcu **slots;
 	unsigned long gap = 0;
-	unsigned long max, min, index;
+	unsigned long max, min;
 	unsigned char offset;
 
 	if (unlikely(mas_is_err(mas)))
@@ -4909,8 +4909,7 @@ static bool mas_rev_awalk(struct ma_state *mas, unsigned long size)
 		min = mas_safe_min(mas, pivots, --offset);
 
 	max = mas_safe_pivot(mas, pivots, offset, type);
-	index = mas->index;
-	while (index <= max) {
+	while (mas->index <= max) {
 		gap = 0;
 		if (gaps)
 			gap = gaps[offset];
@@ -4941,10 +4940,8 @@ static bool mas_rev_awalk(struct ma_state *mas, unsigned long size)
 		min = mas_safe_min(mas, pivots, offset);
 	}
 
-	if (unlikely(index > max)) {
-		mas_set_err(mas, -EBUSY);
-		return false;
-	}
+	if (unlikely((mas->index > max) || (size - 1 > max - mas->index)))
+		goto no_space;
 
 	if (unlikely(ma_is_leaf(type))) {
 		mas->offset = offset;
@@ -4961,9 +4958,11 @@ static bool mas_rev_awalk(struct ma_state *mas, unsigned long size)
 	return false;
 
 ascend:
-	if (mte_is_root(mas->node))
-		mas_set_err(mas, -EBUSY);
+	if (!mte_is_root(mas->node))
+		return false;
 
+no_space:
+	mas_set_err(mas, -EBUSY);
 	return false;
 }
 
diff --git a/lib/test_maple_tree.c b/lib/test_maple_tree.c
index 497fc93ccf9e..ec847bf4dcb4 100644
--- a/lib/test_maple_tree.c
+++ b/lib/test_maple_tree.c
@@ -2517,6 +2517,91 @@ static noinline void check_bnode_min_spanning(struct maple_tree *mt)
 	mt_set_non_kernel(0);
 }
 
+static noinline void check_empty_area_window(struct maple_tree *mt)
+{
+	unsigned long i, nr_entries = 20;
+	MA_STATE(mas, mt, 0, 0);
+
+	for (i = 1; i <= nr_entries; i++)
+		mtree_store_range(mt, i*10, i*10 + 9,
+				  xa_mk_value(i), GFP_KERNEL);
+
+	/* Create another hole besides the one at 0 */
+	mtree_store_range(mt, 160, 169, NULL, GFP_KERNEL);
+
+	/* Check lower bounds that don't fit */
+	rcu_read_lock();
+	MT_BUG_ON(mt, mas_empty_area_rev(&mas, 5, 90, 10) != -EBUSY);
+
+	mas_reset(&mas);
+	MT_BUG_ON(mt, mas_empty_area_rev(&mas, 6, 90, 5) != -EBUSY);
+
+	/* Check lower bound that does fit */
+	mas_reset(&mas);
+	MT_BUG_ON(mt, mas_empty_area_rev(&mas, 5, 90, 5) != 0);
+	MT_BUG_ON(mt, mas.index != 5);
+	MT_BUG_ON(mt, mas.last != 9);
+	rcu_read_unlock();
+
+	/* Check one gap that doesn't fit and one that does */
+	rcu_read_lock();
+	mas_reset(&mas);
+	MT_BUG_ON(mt, mas_empty_area_rev(&mas, 5, 217, 9) != 0);
+	MT_BUG_ON(mt, mas.index != 161);
+	MT_BUG_ON(mt, mas.last != 169);
+
+	/* Check one gap that does fit above the min */
+	mas_reset(&mas);
+	MT_BUG_ON(mt, mas_empty_area_rev(&mas, 100, 218, 3) != 0);
+	MT_BUG_ON(mt, mas.index != 216);
+	MT_BUG_ON(mt, mas.last != 218);
+
+	/* Check size that doesn't fit any gap */
+	mas_reset(&mas);
+	MT_BUG_ON(mt, mas_empty_area_rev(&mas, 100, 218, 16) != -EBUSY);
+
+	/*
+	 * Check size that doesn't fit the lower end of the window but
+	 * does fit the gap
+	 */
+	mas_reset(&mas);
+	MT_BUG_ON(mt, mas_empty_area_rev(&mas, 167, 200, 4) != -EBUSY);
+
+	/*
+	 * Check size that doesn't fit the upper end of the window but
+	 * does fit the gap
+	 */
+	mas_reset(&mas);
+	MT_BUG_ON(mt, mas_empty_area_rev(&mas, 100, 162, 4) != -EBUSY);
+
+	/* Check mas_empty_area forward */
+	mas_reset(&mas);
+	MT_BUG_ON(mt, mas_empty_area(&mas, 0, 100, 9) != 0);
+	MT_BUG_ON(mt, mas.index != 0);
+	MT_BUG_ON(mt, mas.last != 8);
+
+	mas_reset(&mas);
+	MT_BUG_ON(mt, mas_empty_area(&mas, 0, 100, 4) != 0);
+	MT_BUG_ON(mt, mas.index != 0);
+	MT_BUG_ON(mt, mas.last != 3);
+
+	mas_reset(&mas);
+	MT_BUG_ON(mt, mas_empty_area(&mas, 0, 100, 11) != -EBUSY);
+
+	mas_reset(&mas);
+	MT_BUG_ON(mt, mas_empty_area(&mas, 5, 100, 6) != -EBUSY);
+
+	mas_reset(&mas);
+	MT_BUG_ON(mt, mas_empty_area(&mas, 0, 8, 10) != -EBUSY);
+
+	mas_reset(&mas);
+	mas_empty_area(&mas, 100, 165, 3);
+
+	mas_reset(&mas);
+	MT_BUG_ON(mt, mas_empty_area(&mas, 100, 163, 6) != -EBUSY);
+	rcu_read_unlock();
+}
+
 static DEFINE_MTREE(tree);
 static int maple_tree_seed(void)
 {
@@ -2765,6 +2850,10 @@ static int maple_tree_seed(void)
 	check_bnode_min_spanning(&tree);
 	mtree_destroy(&tree);
 
+	mt_init_flags(&tree, MT_FLAGS_ALLOC_RANGE);
+	check_empty_area_window(&tree);
+	mtree_destroy(&tree);
+
 #if defined(BENCH)
 skip:
 #endif
-- 
2.35.1