[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>

5 files changed, 34 insertions, 1 deletions

diff --git a/fs/logfs/gc.c b/fs/logfs/gc.c
index 92949f95a901..e8253e7fb6b2 100644
--- a/fs/logfs/gc.c
+++ b/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;
diff --git a/fs/logfs/journal.c b/fs/logfs/journal.c
index d57c7b07b60b..2c22a4ad5329 100644
--- a/fs/logfs/journal.c
+++ b/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;
 }
diff --git a/fs/logfs/logfs.h b/fs/logfs/logfs.h
index 97195b9e93a5..c9929eed80b1 100644
--- a/fs/logfs/logfs.h
+++ b/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 */
diff --git a/fs/logfs/readwrite.c b/fs/logfs/readwrite.c
index 3659c37fbd72..7e0c39c49719 100644
--- a/fs/logfs/readwrite.c
+++ b/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);
         }
 }
 
diff --git a/fs/logfs/super.c b/fs/logfs/super.c
index 9d856c49afc5..d6e1f4fc3115 100644
--- a/fs/logfs/super.c
+++ b/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)