[PATCH 4.4 02/14] ext4: dont allow overlapping system zones

[Greg Kroah-Hartman]

From: Jan Kara <jack@xxxxxxx>

commit bf9a379d0980e7413d94cb18dac73db2bfc5f470 upstream.

Currently, add_system_zone() just silently merges two added system zones
that overlap. However the overlap should not happen and it generally
suggests that some unrelated metadata overlap which indicates the fs is
corrupted. We should have caught such problems earlier (e.g. in
ext4_check_descriptors()) but add this check as another line of defense.
In later patch we also use this for stricter checking of journal inode
extent tree.

Reviewed-by: Lukas Czerner <lczerner@xxxxxxxxxx>
Signed-off-by: Jan Kara <jack@xxxxxxx>
Link: https://lore.kernel.org/r/20200728130437.7804-3-jack@xxxxxxx
Signed-off-by: Theodore Ts'o <tytso@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 fs/ext4/block_validity.c |   34 ++++++++++++----------------------
 1 file changed, 12 insertions(+), 22 deletions(-)

--- a/fs/ext4/block_validity.c
+++ b/fs/ext4/block_validity.c
@@ -57,7 +57,7 @@ static int add_system_zone(struct ext4_s
 			   ext4_fsblk_t start_blk,
 			   unsigned int count)
 {
-	struct ext4_system_zone *new_entry = NULL, *entry;
+	struct ext4_system_zone *new_entry, *entry;
 	struct rb_node **n = &sbi->system_blks.rb_node, *node;
 	struct rb_node *parent = NULL, *new_node = NULL;
 
@@ -68,30 +68,20 @@ static int add_system_zone(struct ext4_s
 			n = &(*n)->rb_left;
 		else if (start_blk >= (entry->start_blk + entry->count))
 			n = &(*n)->rb_right;
-		else {
-			if (start_blk + count > (entry->start_blk +
-						 entry->count))
-				entry->count = (start_blk + count -
-						entry->start_blk);
-			new_node = *n;
-			new_entry = rb_entry(new_node, struct ext4_system_zone,
-					     node);
-			break;
-		}
+		else	/* Unexpected overlap of system zones. */
+			return -EFSCORRUPTED;
 	}
 
-	if (!new_entry) {
-		new_entry = kmem_cache_alloc(ext4_system_zone_cachep,
-					     GFP_KERNEL);
-		if (!new_entry)
-			return -ENOMEM;
-		new_entry->start_blk = start_blk;
-		new_entry->count = count;
-		new_node = &new_entry->node;
+	new_entry = kmem_cache_alloc(ext4_system_zone_cachep,
+				     GFP_KERNEL);
+	if (!new_entry)
+		return -ENOMEM;
+	new_entry->start_blk = start_blk;
+	new_entry->count = count;
+	new_node = &new_entry->node;
 
-		rb_link_node(new_node, parent, n);
-		rb_insert_color(new_node, &sbi->system_blks);
-	}
+	rb_link_node(new_node, parent, n);
+	rb_insert_color(new_node, &sbi->system_blks);
 
 	/* Can we merge to the left? */
 	node = rb_prev(new_node);