nfsd: Implement NFSv4 FATTR4_CASE_INSENSITIVE and FATTR4_CASE_PRESERVING

NFSD currently provides NFSv4 clients with hard-coded responses
indicating all exported filesystems are case-sensitive and
case-preserving. This is incorrect for case-insensitive filesystems
and ext4 directories with casefold enabled.

Query the underlying filesystem's actual case sensitivity via
nfsd_get_case_info() and return accurate values to clients. This
supports per-directory settings for filesystems that allow mixing
case-sensitive and case-insensitive directories within an export.

The helper queries the parent dentry for non-directory filehandles
because case-folding is a per-directory property. That resolution
has the same corner cases here as for NFSv3 PATHCONF: single-file
exports query an unexported parent, disconnected dentries report
defaults until reconnected, and hardlinked files track whichever
alias the dcache currently holds.

Reviewed-by: Roland Mainz <roland.mainz@nrubsig.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Link: https://patch.msgid.link/20260507-case-sensitivity-v14-14-e62cc8200435@oracle.com
Signed-off-by: Christian Brauner <brauner@kernel.org>

1 files changed, 49 insertions, 3 deletions

diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
index 2a0946c630e1..319007b79d49 100644
--- a/fs/nfsd/nfs4xdr.c
+++ b/fs/nfsd/nfs4xdr.c
@@ -3158,6 +3158,8 @@ struct nfsd4_fattr_args {
 	u32			rdattr_err;
 	bool			contextsupport;
 	bool			ignore_crossmnt;
+	bool			case_insensitive;
+	bool			case_preserving;
 };
 
 typedef __be32(*nfsd4_enc_attr)(struct xdr_stream *xdr,
@@ -3356,6 +3358,33 @@ static __be32 nfsd4_encode_fattr4_acl(struct xdr_stream *xdr,
 	return nfs_ok;
 }
 
+static __be32 nfsd4_encode_fattr4_case_insensitive(struct xdr_stream *xdr,
+					const struct nfsd4_fattr_args *args)
+{
+	return nfsd4_encode_bool(xdr, args->case_insensitive);
+}
+
+static __be32 nfsd4_encode_fattr4_case_preserving(struct xdr_stream *xdr,
+					const struct nfsd4_fattr_args *args)
+{
+	return nfsd4_encode_bool(xdr, args->case_preserving);
+}
+
+static __be32 nfsd4_encode_fattr4_homogeneous(struct xdr_stream *xdr,
+					const struct nfsd4_fattr_args *args)
+{
+	/*
+	 * Casefold-capable filesystems (e.g. ext4 or f2fs with the
+	 * casefold feature) attach a Unicode encoding at mount time
+	 * but apply case folding per directory.  The per-file-system
+	 * case_insensitive and case_preserving values can therefore
+	 * legitimately differ across objects that share the same fsid.
+	 * Report FATTR4_HOMOGENEOUS = FALSE on such filesystems to
+	 * keep that variation consistent with RFC 8881 Section 5.8.2.16.
+	 */
+	return nfsd4_encode_bool(xdr, !sb_has_encoding(args->dentry->d_sb));
+}
+
 static __be32 nfsd4_encode_fattr4_filehandle(struct xdr_stream *xdr,
 					     const struct nfsd4_fattr_args *args)
 {
@@ -3748,8 +3777,8 @@ static const nfsd4_enc_attr nfsd4_enc_fattr4_encode_ops[] = {
 	[FATTR4_ACLSUPPORT]		= nfsd4_encode_fattr4_aclsupport,
 	[FATTR4_ARCHIVE]		= nfsd4_encode_fattr4__noop,
 	[FATTR4_CANSETTIME]		= nfsd4_encode_fattr4__true,
-	[FATTR4_CASE_INSENSITIVE]	= nfsd4_encode_fattr4__false,
-	[FATTR4_CASE_PRESERVING]	= nfsd4_encode_fattr4__true,
+	[FATTR4_CASE_INSENSITIVE]	= nfsd4_encode_fattr4_case_insensitive,
+	[FATTR4_CASE_PRESERVING]	= nfsd4_encode_fattr4_case_preserving,
 	[FATTR4_CHOWN_RESTRICTED]	= nfsd4_encode_fattr4__true,
 	[FATTR4_FILEHANDLE]		= nfsd4_encode_fattr4_filehandle,
 	[FATTR4_FILEID]			= nfsd4_encode_fattr4_fileid,
@@ -3758,7 +3787,7 @@ static const nfsd4_enc_attr nfsd4_enc_fattr4_encode_ops[] = {
 	[FATTR4_FILES_TOTAL]		= nfsd4_encode_fattr4_files_total,
 	[FATTR4_FS_LOCATIONS]		= nfsd4_encode_fattr4_fs_locations,
 	[FATTR4_HIDDEN]			= nfsd4_encode_fattr4__noop,
-	[FATTR4_HOMOGENEOUS]		= nfsd4_encode_fattr4__true,
+	[FATTR4_HOMOGENEOUS]		= nfsd4_encode_fattr4_homogeneous,
 	[FATTR4_MAXFILESIZE]		= nfsd4_encode_fattr4_maxfilesize,
 	[FATTR4_MAXLINK]		= nfsd4_encode_fattr4_maxlink,
 	[FATTR4_MAXNAME]		= nfsd4_encode_fattr4_maxname,
@@ -3968,6 +3997,23 @@ nfsd4_encode_fattr4(struct svc_rqst *rqstp, struct xdr_stream *xdr,
 		args.fhp = tempfh;
 	} else
 		args.fhp = fhp;
+	if (attrmask[0] & (FATTR4_WORD0_CASE_INSENSITIVE |
+			   FATTR4_WORD0_CASE_PRESERVING)) {
+		err = nfsd_get_case_info(dentry, &args.case_insensitive,
+					 &args.case_preserving);
+		/*
+		 * Per RFC 8881 Section 18.7.3, an attribute advertised
+		 * in SUPPORTED_ATTRS must come back with a value or the
+		 * GETATTR must fail. nfsd_get_case_info() fills POSIX
+		 * defaults and returns -EOPNOTSUPP when the underlying
+		 * filesystem does not expose case state; encode those
+		 * defaults so the reply agrees with what SUPPORTED_ATTRS
+		 * advertises. Other errors fail the operation as the
+		 * spec requires.
+		 */
+		if (err && err != -EOPNOTSUPP)
+			goto out_nfserr;
+	}
 
 	if (attrmask[0] & FATTR4_WORD0_ACL) {
 		err = nfsd4_get_nfs4_acl(rqstp, dentry, &args.acl);