ext4: fix crash during online resizing

commit f96c3ac8dfc24b4e38fc4c2eba5fea2107b929d1 upstream.

When computing maximum size of filesystem possible with given number of
group descriptor blocks, we forget to include s_first_data_block into
the number of blocks. Thus for filesystems with non-zero
s_first_data_block it can happen that computed maximum filesystem size
is actually lower than current filesystem size which confuses the code
and eventually leads to a BUG_ON in ext4_alloc_group_tables() hitting on
flex_gd->count == 0. The problem can be reproduced like:

truncate -s 100g /tmp/image
mkfs.ext4 -b 1024 -E resize=262144 /tmp/image 32768
mount -t ext4 -o loop /tmp/image /mnt
resize2fs /dev/loop0 262145
resize2fs /dev/loop0 300000

Fix the problem by properly including s_first_data_block into the
computed number of filesystem blocks.

Fixes: 1c6bd7173d66 "ext4: convert file system to meta_bg if needed..."
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/ext4/resize.c b/fs/ext4/resize.c
index 2fc1564..4bd1224 100644 (file)
--- a/fs/ext4/resize.c
+++ b/fs/ext4/resize.c
@@ -1928,7 +1928,8 @@ retry:
                                le16_to_cpu(es->s_reserved_gdt_blocks);
                        n_group = n_desc_blocks * EXT4_DESC_PER_BLOCK(sb);
                        n_blocks_count = (ext4_fsblk_t)n_group *
-                               EXT4_BLOCKS_PER_GROUP(sb);
+                               EXT4_BLOCKS_PER_GROUP(sb) +
+                               le32_to_cpu(es->s_first_data_block);
                        n_group--; /* set to last group number */
                }