Re: [RFC PATCH 1/2] libfs: Return ENOSPC when the directory offset range is exhausted

[Jeff Layton <jlayton@kernel.org>]

On Sun, 2024-11-17 at 16:32 -0500, cel@kernel.org wrote:
> From: Chuck Lever <chuck.lever@oracle.com>
> 
> Testing shows that the EBUSY error return from mtree_alloc_cyclic()
> leaks into user space. The ERRORS section of "man creat(2)" says:
> 
> > 	EBUSY	O_EXCL was specified in flags and pathname refers
> > 		to a block device that is in use by the system
> > 		(e.g., it is mounted).
> 
> ENOSPC is closer to what applications expect in this situation.
> 
> Note that the normal range of simple directory offset values is
> 2..2^63, so hitting this error is going to be rare to impossible.
> 
> Fixes: 6faddda69f62 ("libfs: Add directory operations for stable offsets")
> Cc: <stable@vger.kernel.org> # v6.9+
> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
> ---
>  fs/libfs.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/libfs.c b/fs/libfs.c
> index 46966fd8bcf9..bf67954b525b 100644
> --- a/fs/libfs.c
> +++ b/fs/libfs.c
> @@ -288,7 +288,9 @@ int simple_offset_add(struct offset_ctx *octx, struct dentry *dentry)
>  
>  	ret = mtree_alloc_cyclic(&octx->mt, &offset, dentry, DIR_OFFSET_MIN,
>  				 LONG_MAX, &octx->next_offset, GFP_KERNEL);
> -	if (ret < 0)
> +	if (unlikely(ret == -EBUSY))
> +		return -ENOSPC;
> +	if (unlikely(ret < 0))
>  		return ret;
>  
>  	offset_set(dentry, offset);

Reviewed-by: Jeff Layton <jlayton@kernel.org>