Re: [PATCH STABLE 5.10 5.4 4.19 4.14] ext4: add check to prevent attempting to resize an fs with sparse_super2

Greg KH
2022-03-14T09:05:53Z

On Sat, Mar 12, 2022 at 11:44:49PM -0500, Theodore Ts'o wrote:
> From: Josh Triplett <josh@joshtriplett.org>
>
> commit b1489186cc8391e0c1e342f9fbc3eedf6b944c61 upstream.
>
> The in-kernel ext4 resize code doesn't support filesystem with the
> sparse_super2 feature. It fails with errors like this and doesn't
> finish the resize:
>
> EXT4-fs (loop0): resizing filesystem from 16640 to 7864320 blocks
> EXT4-fs warning (device loop0): verify_reserved_gdb:760: reserved GDT 2 missing grp 1 (32770)
> EXT4-fs warning (device loop0): ext4_resize_fs:2111: error (-22) occurred during file system resize
> EXT4-fs (loop0): resized filesystem to 2097152
>
> To reproduce:
> mkfs.ext4 -b 4096 -I 256 -J size=32 -E resize=$((256*1024*1024)) -O sparse_super2 ext4.img 65M
> truncate -s 30G ext4.img
> mount ext4.img /mnt
> python3 -c 'import fcntl, os, struct ; fd = os.open("/mnt", os.O_RDONLY | os.O_DIRECTORY) ; fcntl.ioctl(fd, 0x40086610, struct.pack("Q", 30 * 1024 * 1024 * 1024 // 4096), False) ; os.close(fd)'
> dmesg | tail
> e2fsck ext4.img
>
> The userspace resize2fs tool has a check for this case: it checks if
> the filesystem has sparse_super2 set and if the kernel provides
> /sys/fs/ext4/features/sparse_super2. However, the former check
> requires manually reading and parsing the filesystem superblock.
>
> Detect this case in ext4_resize_begin and error out early with a clear
> error message.
>
> Signed-off-by: Josh Triplett <josh@joshtriplett.org>
> Link: https://lore.kernel.org/r/74b8ae78405270211943cd7393e65586c5faeed1.1623093259.git.josh@joshtriplett.org
> Signed-off-by: Theodore Ts'o <tytso@mit.edu>
> ---
> fs/ext4/resize.c | 5 +++++
> 1 file changed, 5 insertions(+)

Now queued up, thanks.

greg k-h