Re: [Ocfs2-devel] [PATCH] ocfs2: check new file size on fallocate call

[Andrew Morton]

On Mon, 29 May 2023 16:26:45 +0100 Luís Henriques via Ocfs2-devel <ocfs2-devel@xxxxxxxxxxxxxx> wrote:

> When changing a file size with fallocate() the new size isn't being
> checked.  In particular, the FSIZE ulimit isn't being checked, which makes
> fstest generic/228 fail.  Simply adding a call to inode_newsize_ok() fixes
> this issue.
> 
> ...
>
> --- a/fs/ocfs2/file.c
> +++ b/fs/ocfs2/file.c
> @@ -2100,14 +2100,20 @@ static long ocfs2_fallocate(struct file *file, int mode, loff_t offset,
>  	struct ocfs2_space_resv sr;
>  	int change_size = 1;
>  	int cmd = OCFS2_IOC_RESVSP64;
> +	int ret = 0;
>  
>  	if (mode & ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE))
>  		return -EOPNOTSUPP;
>  	if (!ocfs2_writes_unwritten_extents(osb))
>  		return -EOPNOTSUPP;
>  
> -	if (mode & FALLOC_FL_KEEP_SIZE)
> +	if (mode & FALLOC_FL_KEEP_SIZE) {
>  		change_size = 0;
> +	} else {
> +		ret = inode_newsize_ok(inode, offset + len);
> +		if (ret)
> +			return ret;
> +	}
>  

So userspace can exceed rlimit(RLIMIT_FSIZE).

Do we think this flaw is serious enough to justify backporting the fix
into earlier -stable kernels?