fix-crash-during-online-resizing

   1 ext4: fix crash during online resizing
   2
   3 From: Jan Kara <jack@suse.cz>
   4
   5 When computing maximum size of filesystem possible with given number of
   6 group descriptor blocks, we forget to include s_first_data_block into
   7 the number of blocks. Thus for filesystems with non-zero
   8 s_first_data_block it can happen that computed maximum filesystem size
   9 is actually lower than current filesystem size which confuses the code
  10 and eventually leads to a BUG_ON in ext4_alloc_group_tables() hitting on
  11 flex_gd->count == 0. The problem can be reproduced like:
  12
  13 truncate -s 100g /tmp/image
  14 mkfs.ext4 -b 1024 -E resize=262144 /tmp/image 32768
  15 mount -t ext4 -o loop /tmp/image /mnt
  16 resize2fs /dev/loop0 262145
  17 resize2fs /dev/loop0 300000
  18
  19 Fix the problem by properly including s_first_data_block into the
  20 computed number of filesystem blocks.
  21
  22 Fixes: 1c6bd7173d66 "ext4: convert file system to meta_bg if needed..."
  23 Signed-off-by: Jan Kara <jack@suse.cz>
  24 Signed-off-by: Theodore Ts'o <tytso@mit.edu>
  25 Cc: stable@vger.kernel.org
  26 ---
  27  fs/ext4/resize.c | 3 ++-
  28  1 file changed, 2 insertions(+), 1 deletion(-)
  29
  30 diff --git a/fs/ext4/resize.c b/fs/ext4/resize.c
  31 index 48421de803b7..3d9b18505c0c 100644
  32 --- a/fs/ext4/resize.c
  33 +++ b/fs/ext4/resize.c
  34 @@ -1960,7 +1960,8 @@ int ext4_resize_fs(struct super_block *sb, ext4_fsblk_t n_blocks_count)
  35                                 le16_to_cpu(es->s_reserved_gdt_blocks);
  36                         n_group = n_desc_blocks * EXT4_DESC_PER_BLOCK(sb);
  37                         n_blocks_count = (ext4_fsblk_t)n_group *
  38 -                               EXT4_BLOCKS_PER_GROUP(sb);
  39 +                               EXT4_BLOCKS_PER_GROUP(sb) +
  40 +                               le32_to_cpu(es->s_first_data_block);
  41                         n_group--; /* set to last group number */
  42                 }
  43
  44 --
  45 2.16.4
  46
  47