[Devel] [PATCH v3 VZ10 1/1] fs: namespace: transform mount flags to comma separated values

[Vladimir Riabchun]

On 6/3/26 14:32, Vasileios Almpanis wrote:
> In legacy mount callpaths, userspace might pass mount options as
> flags. These flags escape our checks in ve_devmnt_process allowing
> devices to be mounted inside containers with options not specified in
> ...
> +/*
> + * For legacy mount(2), MS_* mount flags are folded into fc->sb_flags and are
> + * not present in the monolithic data string.  Build a page with user data
> + * followed by those flags for ve_devmnt checks in vfs_parse_monolithic_sep.
> + *
> + * Returns @data when nothing needs to be added, a new page otherwise, or
> + * ERR_PTR() on failure.  The caller must free_page() when the result != @data.
> + */
> +void *legacy_merge_mount_data(struct fs_context *fc, void *data)
> +{
> +	struct ve_struct *ve = get_exec_env();
> +	size_t off = 0;
> +	char *page;
> +	int err;
> +
> +	if (ve_is_super(ve))
> +		return data;
> +
> +	if (!fc->fs_type || !(fc->fs_type->fs_flags & FS_REQUIRES_DEV))
> +		return data;
> +
> +	/*
> +	 * Filesystems with binary mount data (e.g. btrfs) bypass option
> +	 * string parsing entirely, so our checks cannot apply here.
> +	 */
> +	if (fc->fs_type->fs_flags & FS_BINARY_MOUNTDATA)
> +		return data;
> +
> +	page = (char *)__get_free_page(GFP_KERNEL);
> +	if (!page)
> +		return ERR_PTR(-ENOMEM);
> +
> +	if (data && *(char *)data) {
> +		ssize_t ret = strscpy(page, data, PAGE_SIZE);
> +
> +		if (ret < 0) {
> +			err = -E2BIG;
> +			goto err_free;
> +		}
> +		off = ret;
> +	}
> +
> +	err = vfs_format_sb_flags(fc, page, PAGE_SIZE, &off);
> +	if (err)
> +		goto err_free;
> +
> +	if (!off) {

Let's drop this check. It happens only when data is empty and no flags provided.
And it doesn't add any value - we just free page a little bit earlier.

Everything else looks good.

> +		free_page((unsigned long)page);
> +		return data;
> +	}
> +
> +	return page;
> +
> +err_free:
> +	free_page((unsigned long)page);
> +	return ERR_PTR(err);
> +}
> ...

-- 
Best regards, Riabchun Vladimir
Linux Kernel Developer, Virtuozzo