| From 3ffbdd1f1165f1b2d6a94d1b1aabef57120deaf7 Mon Sep 17 00:00:00 2001 |
| From: Ojaswin Mujoo <ojaswin@linux.ibm.com> |
| Date: Tue, 5 Aug 2025 14:00:31 +0530 |
| Subject: ext4: fix reserved gdt blocks handling in fsmap |
| |
| 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.git.ojaswin@linux.ibm.com |
| 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) |
