[PATCH v12 13/15] nfsd: Report export case-folding via NFSv3 PATHCONF

[Chuck Lever <cel@kernel.org>]

From: Chuck Lever <chuck.lever@oracle.com>

The hard-coded MSDOS_SUPER_MAGIC check in nfsd3_proc_pathconf()
only recognizes FAT filesystems as case-insensitive. Modern
filesystems like F2FS, exFAT, and CIFS support case-insensitive
directories, but NFSv3 clients cannot discover this capability.

Query the export's actual case behavior through ->fileattr_get
instead. This allows NFSv3 clients to correctly handle case
sensitivity for any filesystem that implements the fileattr
interface. Filesystems without ->fileattr_get continue to report
the default POSIX behavior (case-sensitive, case-preserving).

This change depends on the earlier "fat: Implement fileattr_get
for case sensitivity" patch in this series, which ensures FAT
filesystems report their case behavior correctly via the
fileattr interface.

Reviewed-by: Roland Mainz <roland.mainz@nrubsig.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
 fs/nfsd/nfs3proc.c | 36 +++++++++++++++++++++------
 fs/nfsd/vfs.c      | 72 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 fs/nfsd/vfs.h      |  3 +++
 fs/nfsd/xdr3.h     |  4 +--
 4 files changed, 105 insertions(+), 10 deletions(-)

diff --git a/fs/nfsd/nfs3proc.c b/fs/nfsd/nfs3proc.c
index 42adc5461db0..62ebc65b8af2 100644
--- a/fs/nfsd/nfs3proc.c
+++ b/fs/nfsd/nfs3proc.c
@@ -710,23 +710,43 @@ nfsd3_proc_pathconf(struct svc_rqst *rqstp)
 	resp->p_name_max = 255;		/* at least */
 	resp->p_no_trunc = 0;
 	resp->p_chown_restricted = 1;
-	resp->p_case_insensitive = 0;
-	resp->p_case_preserving = 1;
+	resp->p_case_insensitive = false;
+	resp->p_case_preserving = true;
 
 	resp->status = fh_verify(rqstp, &argp->fh, 0, NFSD_MAY_NOP);
 
 	if (resp->status == nfs_ok) {
 		struct super_block *sb = argp->fh.fh_dentry->d_sb;
+		int err;
 
-		/* Note that we don't care for remote fs's here */
-		switch (sb->s_magic) {
-		case EXT2_SUPER_MAGIC:
+		if (sb->s_magic == EXT2_SUPER_MAGIC) {
 			resp->p_link_max = EXT2_LINK_MAX;
 			resp->p_name_max = EXT2_NAME_LEN;
+		}
+
+		err = nfsd_get_case_info(argp->fh.fh_dentry,
+					 &resp->p_case_insensitive,
+					 &resp->p_case_preserving);
+		/*  
+		 * RFC 1813 lists NFS3ERR_STALE, NFS3ERR_BADHANDLE, and
+		 * NFS3ERR_SERVERFAULT as the only PATHCONF errors.
+		 */
+		switch (err) {
+		case 0:
+		case -EOPNOTSUPP:
+			/* Both arms leave the output booleans valid. */
 			break;
-		case MSDOS_SUPER_MAGIC:
-			resp->p_case_insensitive = 1;
-			resp->p_case_preserving  = 0;
+		case -EACCES:
+		case -EPERM:
+			/*
+			 * Policy denied the query. Report STALE so the
+			 * handle is unusable without implying a server
+			 * malfunction.
+			 */
+			resp->status = nfserr_stale;
+			break;
+		default:
+			resp->status = nfserr_serverfault;
 			break;
 		}
 	}
diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
index eafdf7b7890f..4bd63d8efbf7 100644
--- a/fs/nfsd/vfs.c
+++ b/fs/nfsd/vfs.c
@@ -32,6 +32,7 @@
 #include <linux/writeback.h>
 #include <linux/security.h>
 #include <linux/sunrpc/xdr.h>
+#include <linux/fileattr.h>
 
 #include "xdr3.h"
 
@@ -2891,3 +2892,74 @@ nfsd_permission(struct svc_cred *cred, struct svc_export *exp,
 
 	return err? nfserrno(err) : 0;
 }
+
+/**
+ * nfsd_get_case_info - get case sensitivity info for a dentry
+ * @dentry: dentry to query
+ * @case_insensitive: set to true if the filesystem is case-insensitive
+ * @case_preserving: set to true if the filesystem preserves case
+ *
+ * On casefold-capable filesystems the flag lives on the directory,
+ * not on its entries, so for a non-directory @dentry the parent is
+ * queried instead. A directory (including an export root, whose
+ * parent lies outside the export) is queried as-is so its own
+ * contents' lookup behavior is reported.
+ *
+ * When the filesystem does not expose case-folding state (no
+ * ->fileattr_get, or the callback returns -EOPNOTSUPP /
+ * -ENOIOCTLCMD / -ENOTTY / -EINVAL), the outputs are filled with
+ * POSIX defaults (case-sensitive, case-preserving) on the premise
+ * that a filesystem with case-folding support wires up
+ * fileattr_get.
+ *
+ * Other errors propagate unmodified (-EACCES, -EPERM from LSM
+ * hooks; -EIO, -ESTALE, ... from the filesystem). Case-folding
+ * behavior is a property of the exported filesystem, not of the
+ * caller's credentials, so silently substituting defaults would
+ * let the same dentry report POSIX while LSM denies and report
+ * casefolding once LSM allows -- a client could race against
+ * silent name collisions on a case-insensitive export.
+ *
+ * Return: 0 with outputs filled, -EOPNOTSUPP with outputs filled
+ *         to POSIX defaults, or a negative errno with outputs
+ *         unmodified.
+ */
+int
+nfsd_get_case_info(struct dentry *dentry, bool *case_insensitive,
+		   bool *case_preserving)
+{
+	struct file_kattr fa = {};
+	struct dentry *cd;
+	bool put = false;
+	int err;
+
+	if (d_is_dir(dentry)) {
+		cd = dentry;
+	} else {
+		cd = dget_parent(dentry);
+		put = true;
+	}
+	err = vfs_fileattr_get(cd, &fa);
+	if (put)
+		dput(cd);
+	switch (err) {
+	case 0:
+		*case_insensitive = fa.fsx_xflags & FS_XFLAG_CASEFOLD;
+		*case_preserving =
+			!(fa.fsx_xflags & FS_XFLAG_CASENONPRESERVING);
+		return 0;
+	case -EINVAL:
+	case -ENOTTY:
+	case -ENOIOCTLCMD:
+	case -EOPNOTSUPP:
+		/*
+		 * Filesystem does not expose case state.
+		 * Report POSIX defaults.
+		 */
+		*case_insensitive = false;
+		*case_preserving = true;
+		return -EOPNOTSUPP;
+	default:
+		return err;
+	}
+}
diff --git a/fs/nfsd/vfs.h b/fs/nfsd/vfs.h
index 702a844f2106..e09ea04a51b9 100644
--- a/fs/nfsd/vfs.h
+++ b/fs/nfsd/vfs.h
@@ -156,6 +156,9 @@ __be32		nfsd_readdir(struct svc_rqst *, struct svc_fh *,
 			     loff_t *, struct readdir_cd *, nfsd_filldir_t);
 __be32		nfsd_statfs(struct svc_rqst *, struct svc_fh *,
 				struct kstatfs *, int access);
+int		nfsd_get_case_info(struct dentry *dentry,
+				   bool *case_insensitive,
+				   bool *case_preserving);
 
 __be32		nfsd_permission(struct svc_cred *cred, struct svc_export *exp,
 				struct dentry *dentry, int acc);
diff --git a/fs/nfsd/xdr3.h b/fs/nfsd/xdr3.h
index 522067b7fd75..a7c9714b0b0e 100644
--- a/fs/nfsd/xdr3.h
+++ b/fs/nfsd/xdr3.h
@@ -209,8 +209,8 @@ struct nfsd3_pathconfres {
 	__u32			p_name_max;
 	__u32			p_no_trunc;
 	__u32			p_chown_restricted;
-	__u32			p_case_insensitive;
-	__u32			p_case_preserving;
+	bool			p_case_insensitive;
+	bool			p_case_preserving;
 };
 
 struct nfsd3_commitres {

-- 
2.53.0