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0f2bb59b37
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: 0c9ec4beec ("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.git.ojaswin@linux.ibm.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ulrich Hecht <uli@kernel.org>