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ext4: fix corruption when online resizing a 1K bigalloc fs

When a backup superblock is updated in update_backups(), the primary
superblock's offset in the group (that is, sbi->s_sbh->b_blocknr) is used
as the backup superblock's offset in its group. However, when the block
size is 1K and bigalloc is enabled, the two offsets are not equal. This
causes the backup group descriptors to be overwritten by the superblock
in update_backups(). Moreover, if meta_bg is enabled, the file system will
be corrupted because this feature uses backup group descriptors.

To solve this issue, we use a more accurate ext4_group_first_block_no() as
the offset of the backup superblock in its group.

Fixes: d77147ff443b ("ext4: add support for online resizing with bigalloc")
Signed-off-by: Baokun Li <libaokun1@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: stable@kernel.org
Link: https://lore.kernel.org/r/20221117040341.1380702-4-libaokun1@huawei.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

authored by

Baokun Li and committed by
Theodore Ts'o 0aeaa255 8f49ec60

+3 -3
+3 -3
fs/ext4/resize.c
··· 1604 1604 int meta_bg = ext4_has_feature_meta_bg(sb); 1605 1605 sector_t old_gdb = 0; 1606 1606 1607 - update_backups(sb, sbi->s_sbh->b_blocknr, (char *)es, 1608 - sizeof(struct ext4_super_block), 0); 1607 + update_backups(sb, ext4_group_first_block_no(sb, 0), 1608 + (char *)es, sizeof(struct ext4_super_block), 0); 1609 1609 for (; gdb_num <= gdb_num_end; gdb_num++) { 1610 1610 struct buffer_head *gdb_bh; 1611 1611 ··· 1816 1816 if (test_opt(sb, DEBUG)) 1817 1817 printk(KERN_DEBUG "EXT4-fs: extended group to %llu " 1818 1818 "blocks\n", ext4_blocks_count(es)); 1819 - update_backups(sb, EXT4_SB(sb)->s_sbh->b_blocknr, 1819 + update_backups(sb, ext4_group_first_block_no(sb, 0), 1820 1820 (char *)es, sizeof(struct ext4_super_block), 0); 1821 1821 } 1822 1822 return err;