[Devel] [PATCH rh7 v2 2/3] ext4: fix dir corruption when ext4_dx_add_entry() fails

[Konstantin Khorenko]

From: Zhihao Cheng <chengzhihao1 at huawei.com>

Following process may lead to fs corruption:
1. ext4_create(dir/foo)
 ext4_add_nondir
  ext4_add_entry
   ext4_dx_add_entry
     a. add_dirent_to_buf
      ext4_mark_inode_dirty
      ext4_handle_dirty_metadata   // dir inode bh is recorded into journal
     b. ext4_append    // dx_get_count(entries) == dx_get_limit(entries)
       ext4_bread(EXT4_GET_BLOCKS_CREATE)
        ext4_getblk
         ext4_map_blocks
          ext4_ext_map_blocks
            ext4_mb_new_blocks
             dquot_alloc_block
              dquot_alloc_space_nodirty
               inode_add_bytes    // update dir's i_blocks
            ext4_ext_insert_extent
             ext4_ext_dirty  // record extent bh into journal
              ext4_handle_dirty_metadata(bh)
              // record new block into journal
       inode->i_size += inode->i_sb->s_blocksize   // new size(in mem)
     c. ext4_handle_dirty_dx_node(bh2)
        // record dir's new block(dx_node) into journal
     d. ext4_handle_dirty_dx_node((frame - 1)->bh)
     e. ext4_handle_dirty_dx_node(frame->bh)
     f. do_split    // ret err!
     g. add_dirent_to_buf
         ext4_mark_inode_dirty(dir)  // update raw_inode on disk(skipped)
2. fsck -a /dev/sdb
 drop last block(dx_node) which beyonds dir's i_size.
  /dev/sdb: recovering journal
  /dev/sdb contains a file system with errors, check forced.
  /dev/sdb: Inode 12, end of extent exceeds allowed value
        (logical block 128, physical block 3938, len 1)
3. fsck -fn /dev/sdb
 dx_node->entry[i].blk > dir->i_size
  Pass 2: Checking directory structure
  Problem in HTREE directory inode 12 (/dir): bad block number 128.
  Clear HTree index? no
  Problem in HTREE directory inode 12: block #3 has invalid depth (2)
  Problem in HTREE directory inode 12: block #3 has bad max hash
  Problem in HTREE directory inode 12: block #3 not referenced

Fix it by marking inode dirty directly inside ext4_append().
Fetch a reproducer in [Link].

Link: https://bugzilla.kernel.org/show_bug.cgi?id=216466
Cc: stable at vger.kernel.org
Signed-off-by: Zhihao Cheng <chengzhihao1 at huawei.com>
Reviewed-by: Jan Kara <jack at suse.cz>
Link: https://lore.kernel.org/r/20220911045204.516460-1-chengzhihao1@huawei.com
Signed-off-by: Theodore Ts'o <tytso at mit.edu>

[khorenko: backport to 3.10.

 The problem: ext4_append() updates i_size and i_disksize in memory
 but does not journal the inode via ext4_mark_inode_dirty().  If a
 later step in ext4_dx_add_entry() (e.g. do_split()) fails, the new
 i_size never reaches disk.  The extent for the newly allocated block
 is already journaled, but i_size does not cover it - after journal
 recovery fsck drops that block and corrupts the htree.

 The fix: add ext4_mark_inode_dirty(handle, inode) in ext4_append()
 right after updating i_size/i_disksize, so the inode metadata is
 always journaled together with the block allocation.

 Adapted to the older ext4_append() that uses
 ext4_journal_get_write_access(handle, bh) without sb/JTR args.
 Refactored error handling to use a common 'out' label with brelse()
 and ext4_std_error(), matching upstream.]

https://virtuozzo.atlassian.net/browse/PSBM-161670
(cherry picked from commit 7177dd009c7c04290891e9a534cd47d1b620bd04)
Signed-off-by: Konstantin Khorenko <khorenko at virtuozzo.com>
Reviewed-by: Pavel Tikhomirov <ptikhomirov at virtuozzo.com>
---
 fs/ext4/namei.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
index bacdd0630b2c0..4f8636c0ea273 100644
--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -68,14 +68,19 @@ static struct buffer_head *ext4_append(handle_t *handle,
 		return ERR_PTR(err);
 	inode->i_size += inode->i_sb->s_blocksize;
 	EXT4_I(inode)->i_disksize = inode->i_size;
+	err = ext4_mark_inode_dirty(handle, inode);
+	if (err)
+		goto out;
 	BUFFER_TRACE(bh, "get_write_access");
 	err = ext4_journal_get_write_access(handle, bh);
-	if (err) {
-		brelse(bh);
-		ext4_std_error(inode->i_sb, err);
-		return ERR_PTR(err);
-	}
+	if (err)
+		goto out;
 	return bh;
+
+out:
+	brelse(bh);
+	ext4_std_error(inode->i_sb, err);
+	return ERR_PTR(err);
 }
 
 static int ext4_dx_csum_verify(struct inode *inode,
-- 
2.24.3