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fat: fix parent link count when replacing a sibling directory

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vfat_rename() and do_msdos_rename() adjust parent link counts only when
updating the dotdot entry for a move between different parents.  Replacing
an existing empty directory in the same parent also removes a
subdirectory, but leaves the parent's link count unchanged.

For example, renaming one of two sibling directories over the other leaves
the parent with four links instead of three.  stat and ls report the stale
count, and find -links 3 does not match the parent.

Drop the parent's link count for this case after the source entry has been
removed successfully.  Leave cross-parent renames, regular files and the
existing error paths unchanged.

Share the parent link count check with rmdir through fat_dir_drop_nlink().
Only decrement counts of at least three and report a filesystem error
otherwise, rather than reducing a corrupted directory's count below two. 
Export the helper for the VFAT and MSDOS modules.

Link: https://lore.kernel.org/20261030060011.70237-1-dennylin0707@gmail.com
Signed-off-by: Hungyu Lin <dennylin0707@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Cc: Christian Brauner <brauner@kernel.org>
This commit is contained in:
Hungyu Lin 2026-10-30 06:00:11 +00:00 committed by Andrew Morton
parent 0988f0c0c7
commit 6cd4c2736c
4 changed files with 17 additions and 12 deletions
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10
fs/fat/dir.c
View File

@ -963,6 +963,16 @@ int fat_dir_empty(struct inode *dir)
}
EXPORT_SYMBOL_GPL(fat_dir_empty);
void fat_dir_drop_nlink(struct inode *dir)
{
if (dir->i_nlink >= 3)
drop_nlink(dir);
else
fat_fs_error(dir->i_sb, "parent dir link count too low (%u)",
dir->i_nlink);
}
EXPORT_SYMBOL_GPL(fat_dir_drop_nlink);
/*
* fat_subdirs counts the number of sub-directories of dir. It can be run
* on directories being created.

1
fs/fat/fat.h
View File

@ -332,6 +332,7 @@ extern const struct file_operations fat_dir_operations;
extern int fat_search_long(struct inode *inode, const unsigned char *name,
int name_len, struct fat_slot_info *sinfo);
extern int fat_dir_empty(struct inode *dir);
void fat_dir_drop_nlink(struct inode *dir);
extern int fat_subdirs(struct inode *dir);
extern int fat_scan(struct inode *dir, const unsigned char *name,
struct fat_slot_info *sinfo);

9
fs/fat/namei_msdos.c
View File

@ -333,12 +333,7 @@ static int msdos_rmdir(struct inode *dir, struct dentry *dentry)
err = fat_remove_entries(dir, &sinfo); /* and releases bh */
if (err)
goto out;
if (dir->i_nlink >= 3)
drop_nlink(dir);
else {
fat_fs_error(sb, "parent dir link count too low (%u)",
dir->i_nlink);
}
fat_dir_drop_nlink(dir);
clear_nlink(inode);
fat_detach(inode);
@ -565,6 +560,8 @@ static int do_msdos_rename(struct inode *old_dir, unsigned char *old_name,
(void)sync_inode_metadata(old_dir, 1);
if (new_inode) {
if (is_dir && old_dir == new_dir)
fat_dir_drop_nlink(old_dir);
drop_nlink(new_inode);
if (is_dir)
drop_nlink(new_inode);

9
fs/fat/namei_vfat.c
View File

@ -809,12 +809,7 @@ static int vfat_rmdir(struct inode *dir, struct dentry *dentry)
err = fat_remove_entries(dir, &sinfo); /* and releases bh */
if (err)
goto out;
if (dir->i_nlink >= 3)
drop_nlink(dir);
else {
fat_fs_error(sb, "parent dir link count too low (%u)",
dir->i_nlink);
}
fat_dir_drop_nlink(dir);
clear_nlink(inode);
fat_truncate_time(inode, NULL, FAT_UPDATE_ATIME | FAT_UPDATE_CMTIME);
@ -1011,6 +1006,8 @@ static int vfat_rename(struct inode *old_dir, struct dentry *old_dentry,
vfat_update_dir_metadata(old_dir, &ts);
if (new_inode) {
if (is_dir && old_dir == new_dir)
fat_dir_drop_nlink(old_dir);
drop_nlink(new_inode);
if (is_dir)
drop_nlink(new_inode);