Corrupted FAT images can leave a directory inode with an incorrect i_nlink (e.g. 2 even though subdirectories exist). rmdir then unconditionally calls drop_nlink(dir) and can drive i_nlink to 0, triggering the WARN_ON in drop_nlink(). Add a sanity check in vfat_rmdir() and msdos_rmdir(): only drop the parent link count when it is at least 3, otherwise report a filesystem error. Fixes: 9a53c3a783c2 ("[PATCH] r/o bind mounts: unlink: monitor i_nlink") Reported-by: Zhiyu Zhang Closes: https://lore.kernel.org/linux-fsdevel/aVN06OKsKxZe6-Kv@casper.infradead.org/T/#t Tested-by: Zhiyu Zhang Signed-off-by: Zhiyu Zhang --- fs/fat/namei_msdos.c | 7 ++++++- fs/fat/namei_vfat.c | 7 ++++++- 2 files changed, 12 insertions(+), 2 deletions(-) diff --git a/fs/fat/namei_msdos.c b/fs/fat/namei_msdos.c index 0b920ee40a7f..262ec1b790b5 100644 --- a/fs/fat/namei_msdos.c +++ b/fs/fat/namei_msdos.c @@ -325,7 +325,12 @@ static int msdos_rmdir(struct inode *dir, struct dentry *dentry) err = fat_remove_entries(dir, &sinfo); /* and releases bh */ if (err) goto out; - drop_nlink(dir); + if (dir->i_nlink >= 3) + drop_nlink(dir); + else { + fat_fs_error(sb, "parent dir link count too low (%u)", + dir->i_nlink); + } clear_nlink(inode); fat_truncate_time(inode, NULL, S_CTIME); diff --git a/fs/fat/namei_vfat.c b/fs/fat/namei_vfat.c index 5dbc4cbb8fce..47ff083cfc7e 100644 --- a/fs/fat/namei_vfat.c +++ b/fs/fat/namei_vfat.c @@ -803,7 +803,12 @@ static int vfat_rmdir(struct inode *dir, struct dentry *dentry) err = fat_remove_entries(dir, &sinfo); /* and releases bh */ if (err) goto out; - drop_nlink(dir); + if (dir->i_nlink >= 3) + drop_nlink(dir); + else { + fat_fs_error(sb, "parent dir link count too low (%u)", + dir->i_nlink); + } clear_nlink(inode); fat_truncate_time(inode, NULL, S_ATIME|S_MTIME); -- 2.34.1