[LogFS] Prevent memory corruption on large deletes

Removing sufficiently large files would create aliases for a large
number of segments.  This in turn results in a large number of journal
entries and an overflow of s_je_array.

Cheap fix is to add a BUG_ON, turning memory corruption into something
annoying, but less dangerous.  Real fix is to count the number of
affected segments and prevent the problem completely.
Signed-off-by: Joern Engel <joern@logfs.org>

fs/logfs/gc.c

@@ -458,6 +458,14 @@ static void __logfs_gc_pass(struct super_block *sb, int target)
 	struct logfs_block *block;
 	int round, progress, last_progress = 0;
 
+	/*
+	 * Doing too many changes to the segfile at once would result
+	 * in a large number of aliases.  Write the journal before
+	 * things get out of hand.
+	 */
+	if (super->s_shadow_tree.no_shadowed_segments >= MAX_OBJ_ALIASES)
+		logfs_write_anchor(sb);
+
 	if (no_free_segments(sb) >= target &&
 			super->s_no_object_aliases < MAX_OBJ_ALIASES)
 		return;

fs/logfs/journal.c

@@ -493,6 +493,8 @@ static void account_shadows(struct super_block *sb)
 
 	btree_grim_visitor64(&tree->new, (unsigned long)sb, account_shadow);
 	btree_grim_visitor64(&tree->old, (unsigned long)sb, account_shadow);
+	btree_grim_visitor32(&tree->segment_map, 0, NULL);
+	tree->no_shadowed_segments = 0;
 
 	if (li->li_block) {
 		/*
@@ -660,6 +662,7 @@ static int logfs_write_je_buf(struct super_block *sb, void *buf, u16 type,
 	if (ofs < 0)
 		return ofs;
 	logfs_buf_write(area, ofs, super->s_compressed_je, len);
+	BUG_ON(super->s_no_je >= MAX_JOURNAL_ENTRIES);
 	super->s_je_array[super->s_no_je++] = cpu_to_be64(ofs);
 	return 0;
 }

fs/logfs/logfs.h

@@ -257,10 +257,14 @@ struct logfs_shadow {
  * struct shadow_tree
  * @new:			shadows where old_ofs==0, indexed by new_ofs
  * @old:			shadows where old_ofs!=0, indexed by old_ofs
+ * @segment_map:		bitfield of segments containing shadows
+ * @no_shadowed_segment:	number of segments containing shadows
  */
 struct shadow_tree {
 	struct btree_head64 new;
 	struct btree_head64 old;
+	struct btree_head32 segment_map;
+	int no_shadowed_segments;
 };
 
 struct object_alias_item {
@@ -311,6 +315,8 @@ struct logfs_block_ops {
 			write_alias_t *write_one_alias);
 };
 
+#define MAX_JOURNAL_ENTRIES 256
+
 struct logfs_super {
 	struct mtd_info *s_mtd;			/* underlying device */
 	struct block_device *s_bdev;		/* underlying device */
@@ -377,7 +383,7 @@ struct logfs_super {
 	u32	 s_journal_ec[LOGFS_JOURNAL_SEGS]; /* journal erasecounts */
 	u64	 s_last_version;
 	struct logfs_area *s_journal_area;	/* open journal segment */
-	__be64	s_je_array[64];
+	__be64	s_je_array[MAX_JOURNAL_ENTRIES];
 	int	s_no_je;
 
 	int	 s_sum_index;			/* for the 12 summaries */

fs/logfs/readwrite.c

@@ -1219,6 +1219,18 @@ static void free_shadow(struct inode *inode, struct logfs_shadow *shadow)
 	mempool_free(shadow, super->s_shadow_pool);
 }
 
+static void mark_segment(struct shadow_tree *tree, u32 segno)
+{
+	int err;
+
+	if (!btree_lookup32(&tree->segment_map, segno)) {
+		err = btree_insert32(&tree->segment_map, segno, (void *)1,
+				GFP_NOFS);
+		BUG_ON(err);
+		tree->no_shadowed_segments++;
+	}
+}
+
 /**
  * fill_shadow_tree - Propagate shadow tree changes due to a write
  * @inode:	Inode owning the page
@@ -1266,6 +1278,8 @@ static void fill_shadow_tree(struct inode *inode, struct page *page,
 
 		super->s_dirty_used_bytes += shadow->new_len;
 		super->s_dirty_free_bytes += shadow->old_len;
+		mark_segment(tree, shadow->old_ofs >> super->s_segshift);
+		mark_segment(tree, shadow->new_ofs >> super->s_segshift);
 	}
 }
 

fs/logfs/super.c

@@ -451,6 +451,8 @@ static int logfs_read_sb(struct super_block *sb, int read_only)
 
 	btree_init_mempool64(&super->s_shadow_tree.new, super->s_btree_pool);
 	btree_init_mempool64(&super->s_shadow_tree.old, super->s_btree_pool);
+	btree_init_mempool32(&super->s_shadow_tree.segment_map,
+			super->s_btree_pool);
 
 	ret = logfs_init_mapping(sb);
 	if (ret)