Re: [PATCH] nfsd: Fix dentry refcount leak in nfsd_set_fh_dentry()

[NeilBrown]

On Sun, 05 Jul 2026, Guangshuo Li wrote:
> nfsd_set_fh_dentry() gets a dentry reference before checking whether an
> NFSv2 or NFSv3 filehandle resolves to a V4ROOT export. Such filehandles
> are rejected, but the rejection path jumps to out before the dentry is
> stored in fhp->fh_dentry.
> 
> As a result, fh_put() will not see the dentry, and the out path only
> drops the export reference. The dentry reference obtained by dget() or
> exportfs_decode_fh_raw() is therefore leaked.
> 
> Add a separate error path for the V4ROOT rejection case that drops the
> dentry reference before dropping the export reference.
> 
> Fixes: 8a7348a9ed70 ("nfsd: fix refcount leak in nfsd_set_fh_dentry()")
> Signed-off-by: Guangshuo Li <lgs201920130244@xxxxxxxxx>

Thanks for finding and reporting that.

Reviewed-by: NeilBrown <neil@xxxxxxxxxx>

NeilBrown


> ---
>  fs/nfsd/nfsfh.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/nfsd/nfsfh.c b/fs/nfsd/nfsfh.c
> index 429ca5c6ec08..2ca5bb5b5e88 100644
> --- a/fs/nfsd/nfsfh.c
> +++ b/fs/nfsd/nfsfh.c
> @@ -345,20 +345,22 @@ static __be32 nfsd_set_fh_dentry(struct svc_rqst *rqstp, struct net *net,
>  			fhp->fh_no_wcc = true;
>  		fhp->fh_64bit_cookies = true;
>  		if (exp->ex_flags & NFSEXP_V4ROOT)
> -			goto out;
> +			goto out_dput;
>  		break;
>  	case NFS_FHSIZE:
>  		fhp->fh_no_wcc = true;
>  		if (EX_WGATHER(exp))
>  			fhp->fh_use_wgather = true;
>  		if (exp->ex_flags & NFSEXP_V4ROOT)
> -			goto out;
> +			goto out_dput;
>  	}
>  
>  	fhp->fh_dentry = dentry;
>  	fhp->fh_export = exp;
>  
>  	return 0;
> +out_dput:
> +	dput(dentry);
>  out:
>  	exp_put(exp);
>  	return error;
> -- 
> 2.43.0
> 
>