hfs: fix incorrect inode ID assignment in hfs_new_inode()

The xfstests' test-case generic/003 reveals the HFS volume
corruption:

sudo ./check generic/003
FSTYP -- hfs
PLATFORM -- Linux/x86_64 hfsplus-testing-0001 7.0.0-rc1+ #18 SMP PREEMPT_DYNAMIC Fri Mar 13 17:54:19 PDT 2026
MKFS_OPTIONS -- /dev/loop51
MOUNT_OPTIONS -- /dev/loop51 /mnt/scratch

generic/003 51s ... _check_generic_filesystem: filesystem on /dev/loop51 is inconsistent

sudo fsck.hfs -d /dev/loop51
** /dev/loop51
Using cacheBlockSize=32K cacheTotalBlock=1024 cacheSize=32768K.
Executing fsck_hfs (version 540.1-Linux).
** Checking HFS volume.
The volume name is untitled
** Checking extents overflow file.
** Checking catalog file.
** Checking catalog hierarchy.
** Checking volume bitmap.
** Checking volume information.
invalid MDB drNxtCNID
Master Directory Block needs minor repair
(1, 0)
Verify Status: VIStat = 0x8000, ABTStat = 0x0000 EBTStat = 0x0000
CBTStat = 0x0000 CatStat = 0x00000000
** Repairing volume.
** Rechecking volume.
** Checking HFS volume.
The volume name is untitled
** Checking extents overflow file.
** Checking catalog file.
** Checking catalog hierarchy.
** Checking volume bitmap.
** Checking volume information.
** The volume untitled was repaired successfully.

The reason of corruption is incorrect value of drNxtCNID (next
CNID) in the MDB or superblock. The generic/003 test-case
creates several new inodes:

kernel: run fstests generic/003
hfs: hfs_mdb_get():179 next_id 16
hfs: hfs_mdb_get():179 next_id 16
hfs: hfs_new_inode():208 next_id 17
hfs: hfs_new_inode():208 next_id 18
hfs: hfs_mdb_commit():307 next_id 18
hfs: hfs_mdb_get():179 next_id 18
hfs: hfs_new_inode():208 next_id 19
hfs: hfs_new_inode():208 next_id 20
hfs_mdb_commit():307 next_id 20
hfs: hfs_mdb_get():179 next_id 20
hfs: hfs_new_inode():208 next_id 21
hfs: hfs_mdb_commit():307 next_id 21
hfs: hfs_mdb_get():179 next_id 21

The final assigned CNID was 21 but fsck correct it on 22.
It is possible to see that the reason of the issue is
incrementing the next_id value at first and assigning
already incremented value to the inode->i_ino:

struct inode *hfs_new_inode(...)
{
<skipped>

    next_id = atomic64_inc_return(&HFS_SB(sb)->next_id);
<skipped>
    inode->i_ino = (u32)next_id;

<skipped>
}

This patch fixes the issue by assigning the decremented
value to inode->i_ino.

Fixes: a06ec28 ("hfs: add logic of correcting a next unused CNID")
cc: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
cc: Yangtao Li <frank.li@vivo.com>
cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Viacheslav Dubeyko <slava@dubeyko.com>
Link: https://lore.kernel.org/r/20260514195518.354108-2-slava@dubeyko.com
Signed-off-by: Viacheslav Dubeyko <slava@dubeyko.com>

Author: dubeyko

fs/hfs/inode.c

@@ -204,7 +204,7 @@ struct inode *hfs_new_inode(struct inode *dir, const struct qstr *name, umode_t
 		pr_err("cannot create new inode: next CNID exceeds limit\n");
 		goto out_discard;
 	}
-	inode->i_ino = (u32)next_id;
+	inode->i_ino = (u32)next_id - 1;
 	inode->i_mode = mode;
 	inode->i_uid = current_fsuid();
 	inode->i_gid = current_fsgid();