From: Mike Kravetz <mike.kravetz@xxxxxxxxxx> Subject: hugetlbfs: prevent filesystem stacking of hugetlbfs syzbot found issues with having hugetlbfs on a union/overlay as reported in [1]. Due to the limitations (no write) and special functionality of hugetlbfs, it does not work well in filesystem stacking. There are no know use cases for hugetlbfs stacking. Rather than making modifications to get hugetlbfs working in such environments, simply prevent stacking. [1] https://lore.kernel.org/linux-mm/000000000000b4684e05a2968ca6@xxxxxxxxxx/ Link: http://lkml.kernel.org/r/80f869aa-810d-ef6c-8888-b46cee135907@xxxxxxxxxx Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx> Reported-by: syzbot+d6ec23007e951dadf3de@xxxxxxxxxxxxxxxxxxxxxxxxx Suggested-by: Amir Goldstein <amir73il@xxxxxxxxx> Acked-by: Miklos Szeredi <mszeredi@xxxxxxxxxx> Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx> Cc: Colin Walters <walters@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- fs/hugetlbfs/inode.c | 6 ++++++ 1 file changed, 6 insertions(+) --- a/fs/hugetlbfs/inode.c~hugetlbfs-prevent-filesystem-stacking-of-hugetlbfs +++ a/fs/hugetlbfs/inode.c @@ -1364,6 +1364,12 @@ hugetlbfs_fill_super(struct super_block sb->s_magic = HUGETLBFS_MAGIC; sb->s_op = &hugetlbfs_ops; sb->s_time_gran = 1; + + /* + * Due to the special and limited functionality of hugetlbfs, it does + * not work well as a stacking filesystem. + */ + sb->s_stack_depth = FILESYSTEM_MAX_STACK_DEPTH; sb->s_root = d_make_root(hugetlbfs_get_root(sb, ctx)); if (!sb->s_root) goto out_free; _
