Re: [PATCH] fat: Support fallocate on fat.

OGAWA Hirofumi
2012-07-08T13:07:04Z

> +/*
> + * preallocate space for a file. This implements fat's fallocate file
> + * operation, which gets called from sys_fallocate system call. User
> + * space requests len bytes at offset.If FALLOC_FL_KEEP_SIZE is set
> + * we just allocate clusters without zeroing them out.Otherwise we
> + * allocate and zero out clusters via an expanding truncate.
> + */
> +static long fat_fallocate(struct file *file, int mode,
> + loff_t offset, loff_t len)
> +{
> + int err = 0;
> + struct inode *inode = file->f_mapping->host;
> + int cluster, nr_cluster, fclus, dclus, free_bytes, nr_bytes;
> + struct super_block *sb = inode->i_sb;
> + struct msdos_sb_info *sbi = MSDOS_SB(sb);

What happens if called for directory? And does this guarantee it never
expose the uninitialized data userland?

> + /* No support for hole punch or other fallocate flags. */
> + if (mode & ~FALLOC_FL_KEEP_SIZE)
> + return -EOPNOTSUPP;
>
> + if ((offset + len) <= MSDOS_I(inode)->mmu_private) {
> + fat_msg(sb, KERN_ERR,
> + "fat_fallocate():Blocks already allocated");
> + return -EINVAL;
> + }

Please don't output any message by user error. And EINVAL is right
behavior if (offset + len) < allocated size? Sounds like strange design.

> + if ((mode & FALLOC_FL_KEEP_SIZE)) {
> + /* First compute the number of clusters to be allocated */
> + if (inode->i_size > 0) {
> + err = fat_get_cluster(inode, FAT_ENT_EOF,
> + &fclus, &dclus);
> + if (err < 0) {
> + fat_msg(sb, KERN_ERR,
> + "fat_fallocate():fat_get_cluster() error");

Use "%s" and __func__. And looks like the error is normal
(e.g. ENOSPC), so I don't see why it needs to report.

[...]

> + /*
> + * calculate i_blocks and mmu_private from the actual number of
> + * allocated clusters instead of doing it from file size.This ensures
> + * that the preallocated disk space using FALLOC_FL_KEEP_SIZE is
> + * persistent across remounts and writes go into the allocated clusters.
> + */
> + fat_calc_dir_size(inode);

Looks like the wrong. If you didn't initialize preallocated space, the
data never be exposed to userland. It is security bug.

> inode->i_blocks = ((inode->i_size + (sbi->cluster_size - 1))
> & ~((loff_t)sbi->cluster_size - 1)) >> 9;
> + MSDOS_I(inode)->mmu_private = inode->i_size;
> + /* restore i_size */
> + inode->i_size = le32_to_cpu(de->size);
>
> fat_time_fat2unix(sbi, &inode->i_mtime, de->time, de->date, 0);
> if (sbi->options.isvfat) {