5.10-stable review patch. If anyone has any objections, please let me know.
------------------
From: Ojaswin Mujoo ojaswin@linux.ibm.com
commit 3ffbdd1f1165f1b2d6a94d1b1aabef57120deaf7 upstream.
In some cases like small FSes with no meta_bg and where the resize doesn't need extra gdt blocks as it can fit in the current one, s_reserved_gdt_blocks is set as 0, which causes fsmap to emit a 0 length entry, which is incorrect.
$ mkfs.ext4 -b 65536 -O bigalloc /dev/sda 5G $ mount /dev/sda /mnt/scratch $ xfs_io -c "fsmap -d" /mnt/scartch
0: 253:48 [0..127]: static fs metadata 128 1: 253:48 [128..255]: special 102:1 128 2: 253:48 [256..255]: special 102:2 0 <---- 0 len entry 3: 253:48 [256..383]: special 102:3 128
Fix this by adding a check for this case.
Cc: stable@kernel.org Fixes: 0c9ec4beecac ("ext4: support GETFSMAP ioctls") Signed-off-by: Ojaswin Mujoo ojaswin@linux.ibm.com Reviewed-by: Darrick J. Wong djwong@kernel.org Link: https://patch.msgid.link/08781b796453a5770112aa96ad14c864fbf31935.1754377641... Signed-off-by: Theodore Ts'o tytso@mit.edu Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/ext4/fsmap.c | 8 ++++++++ 1 file changed, 8 insertions(+)
--- a/fs/ext4/fsmap.c +++ b/fs/ext4/fsmap.c @@ -393,6 +393,14 @@ static unsigned int ext4_getfsmap_find_s /* Reserved GDT blocks */ if (!ext4_has_feature_meta_bg(sb) || metagroup < first_meta_bg) { len = le16_to_cpu(sbi->s_es->s_reserved_gdt_blocks); + + /* + * mkfs.ext4 can set s_reserved_gdt_blocks as 0 in some cases, + * check for that. + */ + if (!len) + return 0; + error = ext4_getfsmap_fill(meta_list, fsb, len, EXT4_FMR_OWN_RESV_GDT); if (error)