Re: [PATCH 04/29] vfs: strengthen checking of file range inputs to generic_remap_checks

Al Viro
2018-10-18T08:40:22Z

On Wed, Oct 17, 2018 at 03:44:43PM -0700, Darrick J. Wong wrote:
> +static int generic_access_check_limits(struct file *file, loff_t pos,
> + loff_t *count)
> +{
> + struct inode *inode = file->f_mapping->host;
> +
> + /* Don't exceed the LFS limits. */
> + if (unlikely(pos + *count > MAX_NON_LFS &&
> + !(file->f_flags & O_LARGEFILE))) {
> + if (pos >= MAX_NON_LFS)
> + return -EFBIG;
> + *count = min(*count, (loff_t)MAX_NON_LFS - pos);

Can that can be different from MAX_NON_LFS - pos?

> + }
> +
> + /*
> + * Don't operate on ranges the page cache doesn't support.
> + *
> + * If we have written data it becomes a short write. If we have
> + * exceeded without writing data we send a signal and return EFBIG.
> + * Linus frestrict idea will clean these up nicely..
> + */
> + if (unlikely(pos >= inode->i_sb->s_maxbytes))
> + return -EFBIG;
> +
> + *count = min(*count, inode->i_sb->s_maxbytes - pos);
> + return 0;
> +}

Anyway, I would rather do this here:

struct inode *inode = file->f_mapping->host;
loff_t max_size = inode->i_sb->s_maxbytes;

if (!(file->f_flags & O_LARGEFILE))
max_size = MAX_NON_LFS;

if (unlikely(pos >= max_size))
return -EFBIG;
*count = min(*count, max_size - pos);
return 0;