[PATCH 2/2] nfsd: vet the opened dentry after setting a delegation

[Jeff Layton <jlayton@xxxxxxxxxx>]

Between opening a file and setting a delegation on it, someone could
rename or unlink the dentry. If this happens, we do not want to grant a
delegation on the open.

On a CLAIM_NULL open, we're opening by filename, and we'll hold the
i_rwsem while when attempting to set a delegation. After getting a
lease, redo the lookup of the file being opened and validate that the
resulting dentry matches the one in the open file description.

Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
---
 fs/nfsd/nfs4state.c | 48 ++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 43 insertions(+), 5 deletions(-)

diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index d2d21fdf5c41..8a8d8c738950 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -5267,11 +5267,38 @@ static int nfsd4_check_conflicting_opens(struct nfs4_client *clp,
 	return 0;
 }
 
+/*
+ * It's possible that between opening the dentry and setting the delegation,
+ * that it has been renamed or unlinked. Redo the lookup to validate that this
+ * hasn't happened.
+ */
+static int
+nfsd4_vet_deleg_dentry(struct nfsd4_open *open, struct nfs4_file *fp,
+		       struct dentry *parent)
+{
+	struct dentry *child;
+
+	lockdep_assert_held(&d_inode(parent)->i_rwsem);
+
+	child = lookup_one_len(open->op_fname, parent, open->op_fnamelen);
+	if (IS_ERR(child))
+		return PTR_ERR(child);
+	dput(child);
+
+	if (child != file_dentry(fp->fi_deleg_file->nf_file))
+		return -EAGAIN;
+
+	return 0;
+}
+
 static struct nfs4_delegation *
-nfs4_set_delegation(struct nfs4_client *clp,
-		    struct nfs4_file *fp, struct nfs4_clnt_odstate *odstate)
+nfs4_set_delegation(struct nfsd4_open *open, struct nfs4_ol_stateid *stp,
+		    struct dentry *parent)
 {
 	int status = 0;
+	struct nfs4_client *clp = stp->st_stid.sc_client;
+	struct nfs4_file *fp = stp->st_stid.sc_file;
+	struct nfs4_clnt_odstate *odstate = stp->st_clnt_odstate;
 	struct nfs4_delegation *dp;
 	struct nfsd_file *nf;
 	struct file_lock *fl;
@@ -5326,6 +5353,13 @@ nfs4_set_delegation(struct nfs4_client *clp,
 		locks_free_lock(fl);
 	if (status)
 		goto out_clnt_odstate;
+
+	if (parent) {
+		status = nfsd4_vet_deleg_dentry(open, fp, parent);
+		if (status)
+			goto out_unlock;
+	}
+
 	status = nfsd4_check_conflicting_opens(clp, fp);
 	if (status)
 		goto out_unlock;
@@ -5381,11 +5415,13 @@ static void nfsd4_open_deleg_none_ext(struct nfsd4_open *open, int status)
  * proper support for them.
  */
 static void
-nfs4_open_delegation(struct nfsd4_open *open, struct nfs4_ol_stateid *stp)
+nfs4_open_delegation(struct nfsd4_open *open, struct nfs4_ol_stateid *stp,
+		     struct dentry *cdentry)
 {
 	struct nfs4_delegation *dp;
 	struct nfs4_openowner *oo = openowner(stp->st_stateowner);
 	struct nfs4_client *clp = stp->st_stid.sc_client;
+	struct dentry *parent = NULL;
 	int cb_up;
 	int status = 0;
 
@@ -5399,6 +5435,8 @@ nfs4_open_delegation(struct nfsd4_open *open, struct nfs4_ol_stateid *stp)
 				goto out_no_deleg;
 			break;
 		case NFS4_OPEN_CLAIM_NULL:
+			parent = cdentry;
+			fallthrough;
 		case NFS4_OPEN_CLAIM_FH:
 			/*
 			 * Let's not give out any delegations till everyone's
@@ -5413,7 +5451,7 @@ nfs4_open_delegation(struct nfsd4_open *open, struct nfs4_ol_stateid *stp)
 		default:
 			goto out_no_deleg;
 	}
-	dp = nfs4_set_delegation(clp, stp->st_stid.sc_file, stp->st_clnt_odstate);
+	dp = nfs4_set_delegation(open, stp, parent);
 	if (IS_ERR(dp))
 		goto out_no_deleg;
 
@@ -5545,7 +5583,7 @@ nfsd4_process_open2(struct svc_rqst *rqstp, struct svc_fh *current_fh, struct nf
 	* Attempt to hand out a delegation. No error return, because the
 	* OPEN succeeds even if we fail.
 	*/
-	nfs4_open_delegation(open, stp);
+	nfs4_open_delegation(open, stp, resp->cstate.current_fh.fh_dentry);
 nodeleg:
 	status = nfs_ok;
 	trace_nfsd_open(&stp->st_stid.sc_stateid);
-- 
2.36.1