Re: [PATCH] nfsd: allow turning off nfsv3 readdir_plus

["J. Bruce Fields" <bfields@fieldses.org>]

On Mon, Aug 04, 2014 at 05:46:47PM -0400, J. Bruce Fields wrote:
> On Mon, Aug 04, 2014 at 11:24:11AM -0400, bfields wrote:
> > +static int
> > +nfsd3_is_readdirplus_supported(struct svc_rqst *rqstp, struct svc_fh *fhp)
> > +{
> > +	struct svc_export *exp;
> > +	int supported = 1; /* fall back to readdirplus supported in case of errors.*/
> > +	int err;
> > +
> > +	err = fh_verify(rqstp, fhp, S_IFDIR, NFSD_MAY_READ);
> > +	if (err) {
> > +		goto out;
> > +	}
> 
> Actually, this isn't right: errors from fh_verify should be returned to
> the client or weird things could happen (e.g. what should have been a
> transient DELAY error could result in the client turning off
> readdirplus).

Apologies, I misread: as the comment above notes, it falls back on
allowing readdirplus when this fails, so I don't think there's a real
bug here.

> And MAY_READ is more than nfsd_readdir actually asks for,
> I think, probably should just be MAY_NOP here.
> 
> I'll fix that up.--b.

But it's probably still better to return the fh_verify error on failure,
as follows.

--b.

diff --git a/fs/nfsd/export.c b/fs/nfsd/export.c
index 72ffd7cce3c3..30a739d896ff 100644
--- a/fs/nfsd/export.c
+++ b/fs/nfsd/export.c
@@ -1145,6 +1145,7 @@ static struct flags {
 	{ NFSEXP_ALLSQUASH, {"all_squash", ""}},
 	{ NFSEXP_ASYNC, {"async", "sync"}},
 	{ NFSEXP_GATHERED_WRITES, {"wdelay", "no_wdelay"}},
+	{ NFSEXP_NOREADDIRPLUS, {"nordirplus", ""}},
 	{ NFSEXP_NOHIDE, {"nohide", ""}},
 	{ NFSEXP_CROSSMOUNT, {"crossmnt", ""}},
 	{ NFSEXP_NOSUBTREECHECK, {"no_subtree_check", ""}},
diff --git a/fs/nfsd/nfs3proc.c b/fs/nfsd/nfs3proc.c
index fa2525b2e9d7..247b06fb400d 100644
--- a/fs/nfsd/nfs3proc.c
+++ b/fs/nfsd/nfs3proc.c
@@ -471,6 +471,14 @@ nfsd3_proc_readdirplus(struct svc_rqst *rqstp, struct nfsd3_readdirargs *argp,
 	resp->buflen = resp->count;
 	resp->rqstp = rqstp;
 	offset = argp->cookie;
+
+	nfserr = fh_verify(rqstp, &resp->fh, S_IFDIR, NFSD_MAY_NOP);
+	if (nfserr)
+		RETURN_STATUS(nfserr);
+
+	if (resp->fh.fh_export->ex_flags & NFSEXP_NOREADDIRPLUS)
+		RETURN_STATUS(nfserr_notsupp);
+
 	nfserr = nfsd_readdir(rqstp, &resp->fh,
 				     &offset,
 				     &resp->common,
diff --git a/include/uapi/linux/nfsd/export.h b/include/uapi/linux/nfsd/export.h
index cf47c313794e..584b6ef3a5e8 100644
--- a/include/uapi/linux/nfsd/export.h
+++ b/include/uapi/linux/nfsd/export.h
@@ -28,7 +28,8 @@
 #define NFSEXP_ALLSQUASH	0x0008
 #define NFSEXP_ASYNC		0x0010
 #define NFSEXP_GATHERED_WRITES	0x0020
-/* 40 80 100 currently unused */
+#define NFSEXP_NOREADDIRPLUS    0x0040
+/* 80 100 currently unused */
 #define NFSEXP_NOHIDE		0x0200
 #define NFSEXP_NOSUBTREECHECK	0x0400
 #define	NFSEXP_NOAUTHNLM	0x0800		/* Don't authenticate NLM requests - just trust */
@@ -47,7 +48,7 @@
  */
 #define	NFSEXP_V4ROOT		0x10000
 /* All flags that we claim to support.  (Note we don't support NOACL.) */
-#define NFSEXP_ALLFLAGS		0x17E3F
+#define NFSEXP_ALLFLAGS		0x1FE7F
 
 /* The flags that may vary depending on security flavor: */
 #define NFSEXP_SECINFO_FLAGS	(NFSEXP_READONLY | NFSEXP_ROOTSQUASH \