Re: [PATCH v2 1/1] NFSD: fix use-after-free in __nfs42_ssc_open()

[Jeff Layton <jlayton@kernel.org>]

On Mon, 2022-12-12 at 07:11 -0800, Dai Ngo wrote:
> Problem caused by source's vfsmount being unmounted but remains
> on the delayed unmount list. This happens when nfs42_ssc_open()
> return errors.
> 
> Fixed by removing nfsd4_interssc_connect(), leave the vfsmount
> for the laundromat to unmount when idle time expires.
> 
> Removed unneeded check for NULL nfsd_net and added pr_warn
> if vfsmount not found on delayed unmount list.
> 
> Reported-by: Xingyuan Mo <hdthky0@gmail.com>
> Signed-off-by: Dai Ngo <dai.ngo@oracle.com>
> ---
>  fs/nfsd/nfs4proc.c | 32 ++++++++------------------------
>  1 file changed, 8 insertions(+), 24 deletions(-)
> 
> diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
> index 8beb2bc4c328..84646df60212 100644
> --- a/fs/nfsd/nfs4proc.c
> +++ b/fs/nfsd/nfs4proc.c
> @@ -1463,13 +1463,6 @@ nfsd4_interssc_connect(struct nl4_server *nss, struct svc_rqst *rqstp,
>  	return status;
>  }
>  
> -static void
> -nfsd4_interssc_disconnect(struct vfsmount *ss_mnt)
> -{
> -	nfs_do_sb_deactive(ss_mnt->mnt_sb);
> -	mntput(ss_mnt);
> -}
> -
>  /*
>   * Verify COPY destination stateid.
>   *
> @@ -1526,10 +1519,6 @@ nfsd4_cleanup_inter_ssc(struct vfsmount *ss_mnt, struct file *filp,
>  	nfsd_file_put(dst);
>  	fput(filp);
>  
> -	if (!nn) {
> -		mntput(ss_mnt);
> -		return;
> -	}
>  	spin_lock(&nn->nfsd_ssc_lock);
>  	timeout = msecs_to_jiffies(nfsd4_ssc_umount_timeout);
>  	list_for_each_entry_safe(ni, tmp, &nn->nfsd_ssc_mount_list, nsui_list) {
> @@ -1548,10 +1537,8 @@ nfsd4_cleanup_inter_ssc(struct vfsmount *ss_mnt, struct file *filp,
>  		}
>  	}
>  	spin_unlock(&nn->nfsd_ssc_lock);
> -	if (!found) {
> -		mntput(ss_mnt);
> -		return;
> -	}
> +	if (!found)
> +		pr_warn("vfsmount not found on delayed unmount list\n");
>  }
>  
>  #else /* CONFIG_NFSD_V4_2_INTER_SSC */
> @@ -1572,11 +1559,6 @@ nfsd4_cleanup_inter_ssc(struct vfsmount *ss_mnt, struct file *filp,
>  {
>  }
>  
> -static void
> -nfsd4_interssc_disconnect(struct vfsmount *ss_mnt)
> -{
> -}
> -
>  static struct file *nfs42_ssc_open(struct vfsmount *ss_mnt,
>  				   struct nfs_fh *src_fh,
>  				   nfs4_stateid *stateid)
> @@ -1762,7 +1744,7 @@ static int nfsd4_do_async_copy(void *data)
>  		struct file *filp;
>  
>  		filp = nfs42_ssc_open(copy->ss_mnt, &copy->c_fh,
> -				      &copy->stateid);
> +					&copy->stateid);
>  		if (IS_ERR(filp)) {
>  			switch (PTR_ERR(filp)) {
>  			case -EBADF:
> @@ -1771,7 +1753,7 @@ static int nfsd4_do_async_copy(void *data)
>  			default:
>  				nfserr = nfserr_offload_denied;
>  			}
> -			nfsd4_interssc_disconnect(copy->ss_mnt);
> +			/* ss_mnt will be unmounted by the laundromat */
>  			goto do_callback;
>  		}
>  		nfserr = nfsd4_do_copy(copy, filp, copy->nf_dst->nf_file,
> @@ -1852,8 +1834,10 @@ nfsd4_copy(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
>  	if (async_copy)
>  		cleanup_async_copy(async_copy);
>  	status = nfserrno(-ENOMEM);
> -	if (nfsd4_ssc_is_inter(copy))
> -		nfsd4_interssc_disconnect(copy->ss_mnt);
> +	/*
> +	 * source's vfsmount of inter-copy will be unmounted
> +	 * by the laundromat
> +	 */
>  	goto out;
>  }
>  

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