[PATCH 1/2] nfsd: pass caller-provided attrmask storage into nfsd4_setup_notify_entry4()

[Jeff Layton]

nfsd4_setup_notify_entry4() stole 3 words from the xdr stream via
xdr_reserve_space() to hold the host-order bmval[3] attrmask that
nfsd4_encode_attr_vals() consumes and ne_attrs.attrmask.element points
at. Stashing host-endian scratch in an XDR stream buffer is fragile:
the buffer layout is not guaranteed by sunrpc, and it blocks moving the
encoder to pages or xdrgen.

The attrmask only needs to live until the enclosing encode call
serializes the notify_entry4, so hand it caller-provided stack storage
instead. The two callers keep the words on the stack: up to three
concurrent entries for a rename in nfsd4_encode_notify_event(), one in
nfsd4_encode_dir_attr_change().

No wire change: the reserved words were never emitted; attr_vals.data/len
are still captured relative to xdr->p.

Assisted-by: LLM
Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
---
 fs/nfsd/nfs4xdr.c | 28 ++++++++++++++--------------
 1 file changed, 14 insertions(+), 14 deletions(-)

diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
index a47eb544b99f..7d1b2d6f57f2 100644
--- a/fs/nfsd/nfs4xdr.c
+++ b/fs/nfsd/nfs4xdr.c
@@ -4378,21 +4378,16 @@ setup_notify_fhandle(struct dentry *dentry, struct nfs4_delegation *dp,
 static bool
 nfsd4_setup_notify_entry4(struct notify_entry4 *ne, struct xdr_stream *xdr,
 			  struct dentry *dentry, struct nfs4_delegation *dp,
-			  struct nfsd_file *nf, char *name, u32 namelen)
+			  struct nfsd_file *nf, char *name, u32 namelen,
+			  u32 *attrmask)
 {
 	struct path path = nf->nf_file->f_path;
 	struct nfsd4_fattr_args args = { };
 	const u32 *reqmask;
-	uint32_t *attrmask;
 	__be32 status;
 	bool parent;
 	int ret;
 
-	/* Reserve space for attrmask */
-	attrmask = xdr_reserve_space(xdr, 3 * sizeof(uint32_t));
-	if (!attrmask)
-		return false;
-
 	ne->ne_file.data = name;
 	ne->ne_file.len = namelen;
 	ne->ne_attrs.attrmask.element = attrmask;
@@ -4476,6 +4471,7 @@ u8 *nfsd4_encode_notify_event(struct xdr_stream *xdr, struct nfsd_notify_event *
 			      struct nfs4_delegation *dp, struct nfsd_file *nf,
 			      u32 *notify_mask)
 {
+	u32 attrmask[3][3] = { };
 	u8 *p = NULL;
 
 	*notify_mask = 0;
@@ -4484,7 +4480,8 @@ u8 *nfsd4_encode_notify_event(struct xdr_stream *xdr, struct nfsd_notify_event *
 		struct notify_remove4 nr = { };
 
 		if (!nfsd4_setup_notify_entry4(&nr.nrm_old_entry, xdr, nne->ne_dentry, dp,
-					       nf, nne->ne_name, nne->ne_namelen))
+					       nf, nne->ne_name, nne->ne_namelen,
+					       attrmask[0]))
 			goto out_err;
 		p = (u8 *)xdr->p;
 		if (!xdrgen_encode_notify_remove4(xdr, &nr))
@@ -4495,14 +4492,16 @@ u8 *nfsd4_encode_notify_event(struct xdr_stream *xdr, struct nfsd_notify_event *
 		struct notify_remove4 old = { };
 
 		if (!nfsd4_setup_notify_entry4(&na.nad_new_entry, xdr, nne->ne_dentry, dp,
-					       nf, nne->ne_name, nne->ne_namelen))
+					       nf, nne->ne_name, nne->ne_namelen,
+					       attrmask[0]))
 			goto out_err;
 
 		/* If a file was overwritten, report it in nad_old_entry */
 		if (nne->ne_target) {
 			if (!nfsd4_setup_notify_entry4(&old.nrm_old_entry, xdr,
 						       NULL, dp, nf,
-						       nne->ne_name, nne->ne_namelen))
+						       nne->ne_name, nne->ne_namelen,
+						       attrmask[1]))
 				goto out_err;
 			na.nad_old_entry.count = 1;
 			na.nad_old_entry.element = &old;
@@ -4521,19 +4520,19 @@ u8 *nfsd4_encode_notify_event(struct xdr_stream *xdr, struct nfsd_notify_event *
 		/* Don't send any attributes in the old_entry since they're the same in new */
 		if (!nfsd4_setup_notify_entry4(&nr.nrn_old_entry.nrm_old_entry, xdr,
 					       NULL, dp, nf, nne->ne_name,
-					       nne->ne_namelen))
+					       nne->ne_namelen, attrmask[0]))
 			goto out_err;
 
 		if (!nfsd4_setup_notify_entry4(&nr.nrn_new_entry.nad_new_entry, xdr,
 					       nne->ne_dentry, dp, nf, newname,
-					       nne->ne_newnamelen))
+					       nne->ne_newnamelen, attrmask[1]))
 			goto out_err;
 
 		/* If a file was overwritten, report it in nad_old_entry */
 		if (nne->ne_target) {
 			if (!nfsd4_setup_notify_entry4(&old.nrm_old_entry, xdr,
 						       NULL, dp, nf, newname,
-						       nne->ne_newnamelen))
+						       nne->ne_newnamelen, attrmask[2]))
 				goto out_err;
 			nr.nrn_new_entry.nad_old_entry.count = 1;
 			nr.nrn_new_entry.nad_old_entry.element = &old;
@@ -4569,11 +4568,12 @@ u8 *nfsd4_encode_dir_attr_change(struct xdr_stream *xdr, struct nfs4_delegation
 {
 	struct dentry *dentry = nf->nf_file->f_path.dentry;
 	struct notify_attr4 na = { };
+	u32 attrmask[3] = { };
 	u8 *p;
 
 	/* RFC 8881 s10.4.3: ne_file must be a zero-length string for dir attrs */
 	if (!nfsd4_setup_notify_entry4(&na.na_changed_entry, xdr,
-				       dentry, dp, nf, "", 0))
+				       dentry, dp, nf, "", 0, attrmask))
 		return ERR_PTR(-ENOBUFS);
 
 	/* No requested attributes to report; omit the event */

-- 
2.55.0