nilfs2: fix slab-out-of-bounds in nilfs_direct_propagate after truncation

Shuangpeng Bai reported that KASAN detected a slab-out-of-bounds error
in nilfs_direct_propagate() during testing.

Analysis revealed that after truncating a file, a node block immediately
below the B-tree root was not deleted.  Instead, it remained in the B-tree
node cache in a dirty state.  The log writer subsequently detected this
block and incorrectly invoked nilfs_direct_propagate() on it, which is
designed to handle only data blocks in direct mapping.

B-tree nodes in the cache are managed by virtual block numbers, and their
logical keys typically exceed the range expected by direct mapping.
Consequently, processing such a node as a direct mapping entry triggers
a slab-out-of-bounds access.

The root cause is that when a B-tree mapping collapses into a direct
mapping during truncation, an intermediate node block pointed to by the
root node is left behind as garbage instead of being explicitly deleted.

This resolves the issue by adding a nilfs_btree_discard() operation
to delete the remaining intermediate node block during the conversion.
A 'deform' flag is added to the bop_delete interface to explicitly signal
that the deletion is part of a mapping transformation.  This allows the
B-tree mapping implementation to perform the necessary cleanup and
discarding of the residual node structure that would be otherwise be left
orphaned after the transition.

Reported-by: Shuangpeng Bai <shuangpeng.kernel@gmail.com>
Closes: https://lore.kernel.org/r/08A3603A-ADB6-484C-9015-9AC1340E6FB8@gmail.com
Fixes: 36a580eb48 ("nilfs2: direct block mapping")
Cc: stable@vger.kernel.org
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Signed-off-by: Viacheslav Dubeyko <slava@dubeyko.com>

fs/nilfs2/bmap.c

@@ -175,7 +175,7 @@ static int nilfs_bmap_do_delete(struct nilfs_bmap *bmap, __u64 key)
 			return ret;
 	}
 
-	return bmap->b_ops->bop_delete(bmap, key);
+	return bmap->b_ops->bop_delete(bmap, key, false);
 }
 
 /**

fs/nilfs2/bmap.h

@@ -63,7 +63,7 @@ struct nilfs_bmap_operations {
 	int (*bop_lookup_contig)(const struct nilfs_bmap *, __u64, __u64 *,
 				 unsigned int);
 	int (*bop_insert)(struct nilfs_bmap *, __u64, __u64);
-	int (*bop_delete)(struct nilfs_bmap *, __u64);
+	int (*bop_delete)(struct nilfs_bmap *bmap, __u64 key, bool deform);
 	void (*bop_clear)(struct nilfs_bmap *);
 
 	int (*bop_propagate)(struct nilfs_bmap *, struct buffer_head *);

fs/nilfs2/btree.c

@@ -1425,6 +1425,28 @@ static void nilfs_btree_shrink(struct nilfs_bmap *btree,
 	path[level].bp_bh = NULL;
 }
 
+/**
+ * nilfs_btree_discard - discard the last node for the mapping transformation
+ * @btree: bmap struct of btree
+ * @path: array of nilfs_btree_path struct
+ * @level: level of the B-tree node being operated on
+ * @keyp: argument for passing a key (unused)
+ * @ptrp: argument for passing a pointer (unused)
+ */
+static void nilfs_btree_discard(struct nilfs_bmap *btree,
+				struct nilfs_btree_path *path, int level,
+				__u64 *keyp, __u64 *ptrp)
+{
+	struct nilfs_btree_node *root = nilfs_btree_get_root(btree);
+
+	nilfs_btree_node_delete(root, 0, NULL, NULL,
+				NILFS_BTREE_ROOT_NCHILDREN_MAX);
+	nilfs_btree_node_set_level(root, level);
+
+	nilfs_btnode_delete(path[level].bp_bh);
+	path[level].bp_bh = NULL;
+}
+
 static void nilfs_btree_nop(struct nilfs_bmap *btree,
 			    struct nilfs_btree_path *path,
 			    int level, __u64 *keyp, __u64 *ptrp)
@@ -1435,7 +1457,7 @@ static int nilfs_btree_prepare_delete(struct nilfs_bmap *btree,
 				      struct nilfs_btree_path *path,
 				      int *levelp,
 				      struct nilfs_bmap_stats *stats,
-				      struct inode *dat)
+				      struct inode *dat, bool deform)
 {
 	struct buffer_head *bh;
 	struct nilfs_btree_node *node, *parent, *sib;
@@ -1522,15 +1544,17 @@ static int nilfs_btree_prepare_delete(struct nilfs_bmap *btree,
 			if (nilfs_btree_node_get_nchildren(node) - 1 <=
 			    NILFS_BTREE_ROOT_NCHILDREN_MAX) {
 				path[level].bp_op = nilfs_btree_shrink;
-				stats->bs_nblocks += 2;
-				level++;
-				path[level].bp_op = nilfs_btree_nop;
-				goto shrink_root_child;
+			} else if (deform) {
+				path[level].bp_op = nilfs_btree_discard;
 			} else {
 				path[level].bp_op = nilfs_btree_do_delete;
 				stats->bs_nblocks++;
 				goto out;
 			}
+			stats->bs_nblocks += 2;
+			level++;
+			path[level].bp_op = nilfs_btree_nop;
+			goto shrink_root_child;
 		}
 	}
 
@@ -1581,7 +1605,7 @@ static void nilfs_btree_commit_delete(struct nilfs_bmap *btree,
 		nilfs_bmap_set_dirty(btree);
 }
 
-static int nilfs_btree_delete(struct nilfs_bmap *btree, __u64 key)
+static int nilfs_btree_delete(struct nilfs_bmap *btree, __u64 key, bool deform)
 
 {
 	struct nilfs_btree_path *path;
@@ -1601,7 +1625,8 @@ static int nilfs_btree_delete(struct nilfs_bmap *btree, __u64 key)
 
 	dat = NILFS_BMAP_USE_VBN(btree) ? nilfs_bmap_get_dat(btree) : NULL;
 
-	ret = nilfs_btree_prepare_delete(btree, path, &level, &stats, dat);
+	ret = nilfs_btree_prepare_delete(btree, path, &level, &stats, dat,
+			deform);
 	if (ret < 0)
 		goto out;
 	nilfs_btree_commit_delete(btree, path, level, dat);

fs/nilfs2/direct.c

@@ -144,7 +144,7 @@ static int nilfs_direct_insert(struct nilfs_bmap *bmap, __u64 key, __u64 ptr)
 	return ret;
 }
 
-static int nilfs_direct_delete(struct nilfs_bmap *bmap, __u64 key)
+static int nilfs_direct_delete(struct nilfs_bmap *bmap, __u64 key, bool deform)
 {
 	union nilfs_bmap_ptr_req req;
 	struct inode *dat;
@@ -234,7 +234,7 @@ int nilfs_direct_delete_and_convert(struct nilfs_bmap *bmap,
 	/* no need to allocate any resource for conversion */
 
 	/* delete */
-	ret = bmap->b_ops->bop_delete(bmap, key);
+	ret = bmap->b_ops->bop_delete(bmap, key, true);
 	if (ret < 0)
 		return ret;