fix-ext4_check_descriptors

   1 ext4: fix false negatives *and* false positives in ext4_check_descriptors()
   2
   3 Ext4_check_descriptors() was getting called before s_gdb_count was
   4 initialized.  So for file systems w/o the meta_bg feature, allocation
   5 bitmaps could overlap the block group descriptors and ext4 wouldn't
   6 notice.
   7
   8 For file systems with the meta_bg feature enabled, there was a
   9 fencepost error which would cause the ext4_check_descriptors() to
  10 incorrectly believe that the block allocation bitmap overlaps with the
  11 block group descriptor blocks, and it would reject the mount.
  12
  13 Fix both of these problems.
  14
  15 Signed-off-by: Theodore Ts'o <tytso@mit.edu>
  16 Cc: stable@vger.kernel.org
  17 ---
  18 diff --git a/fs/ext4/super.c b/fs/ext4/super.c
  19 index f36c9f774e83..90d0e113a174 100644
  20 --- a/fs/ext4/super.c
  21 +++ b/fs/ext4/super.c
  22 @@ -2348,7 +2348,7 @@ static int ext4_check_descriptors(struct super_block *sb,
  23         struct ext4_sb_info *sbi = EXT4_SB(sb);
  24         ext4_fsblk_t first_block = le32_to_cpu(sbi->s_es->s_first_data_block);
  25         ext4_fsblk_t last_block;
  26 -       ext4_fsblk_t last_bg_block = sb_block + ext4_bg_num_gdb(sb, 0) + 1;
  27 +       ext4_fsblk_t last_bg_block = sb_block + ext4_bg_num_gdb(sb, 0);
  28         ext4_fsblk_t block_bitmap;
  29         ext4_fsblk_t inode_bitmap;
  30         ext4_fsblk_t inode_table;
  31 @@ -4092,14 +4092,13 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
  32                         goto failed_mount2;
  33                 }
  34         }
  35 +       sbi->s_gdb_count = db_count;
  36         if (!ext4_check_descriptors(sb, logical_sb_block, &first_not_zeroed)) {
  37                 ext4_msg(sb, KERN_ERR, "group descriptors corrupted!");
  38                 ret = -EFSCORRUPTED;
  39                 goto failed_mount2;
  40         }
  41
  42 -       sbi->s_gdb_count = db_count;
  43 -
  44         timer_setup(&sbi->s_err_report, print_daily_error_info, 0);
  45
  46         /* Register extent status tree shrinker */