5 files changed, 67 insertions, 5 deletions
diff --git a/sbin/mount/getmntopts.c b/sbin/mount/getmntopts.c
index fb739c6406ae..0ee6d99ed8b9 100644
--- a/sbin/mount/getmntopts.c
+++ b/sbin/mount/getmntopts.c
@@ -139,6 +139,20 @@ checkpath(const char *path, char *resolved)
 	return (0);
 }
 
+int
+checkpath_allow_file(const char *path, char *resolved)
+{
+	struct stat sb;
+
+	if (realpath(path, resolved) == NULL || stat(resolved, &sb) != 0)
+		return (1);
+	if (!S_ISDIR(sb.st_mode) && !S_ISREG(sb.st_mode)) {
+		errno = ENOTDIR;
+		return (1);
+	}
+	return (0);
+}
+
 void
 build_iovec(struct iovec **iov, int *iovlen, const char *name, void *val,
 	    size_t len)
diff --git a/sbin/mount/mntopts.h b/sbin/mount/mntopts.h
index 183d6d9e501d..1d8b80069355 100644
--- a/sbin/mount/mntopts.h
+++ b/sbin/mount/mntopts.h
@@ -103,6 +103,7 @@ struct mntopt {
 void getmntopts(const char *, const struct mntopt *, int *, int *);
 void rmslashes(char *, char *);
 int checkpath(const char *, char resolved_path[]);
+int checkpath_allow_file(const char *, char resolved_path[]);
 extern int getmnt_silent;
 void build_iovec(struct iovec **iov, int *iovlen, const char *name, void *val, size_t len);
 void build_iovec_argf(struct iovec **iov, int *iovlen, const char *name, const char *fmt, ...);
diff --git a/sbin/mount/mount.c b/sbin/mount/mount.c
index cbb2a8784e26..66c1c1d1d000 100644
--- a/sbin/mount/mount.c
+++ b/sbin/mount/mount.c
@@ -89,6 +89,7 @@ struct statfs *getmntpt(const char *);
 int	hasopt(const char *, const char *);
 int	ismounted(struct fstab *, struct statfs *, int);
 int	isremountable(const char *);
+int	allow_file_mount(const char *);
 void	mangle(char *, struct cpa *);
 char   *update_options(char *, char *, int);
 int	mountfs(const char *, const char *, const char *,
@@ -528,6 +529,15 @@ isremountable(const char *vfsname)
 }
 
 int
+allow_file_mount(const char *vfsname)
+{
+
+	if (strcmp(vfsname, "nullfs") == 0)
+		return (1);
+	return (0);
+}
+
+int
 hasopt(const char *mntopts, const char *option)
 {
 	int negative, found;
@@ -573,9 +583,16 @@ mountfs(const char *vfstype, const char *spec, const char *name, int flags,
 	static struct cpa mnt_argv;
 
 	/* resolve the mountpoint with realpath(3) */
-	if (checkpath(name, mntpath) != 0) {
-		xo_warn("%s", mntpath);
-		return (1);
+	if (allow_file_mount(vfstype)) {
+		if (checkpath_allow_file(name, mntpath) != 0) {
+			xo_warn("%s", mntpath);
+			return (1);
+		}
+	} else {
+		if (checkpath(name, mntpath) != 0) {
+			xo_warn("%s", mntpath);
+			return (1);
+		}
 	}
 	name = mntpath;
 
diff --git a/sbin/mount_nullfs/mount_nullfs.8 b/sbin/mount_nullfs/mount_nullfs.8
index f2969209e240..46e55d8a7d54 100644
--- a/sbin/mount_nullfs/mount_nullfs.8
+++ b/sbin/mount_nullfs/mount_nullfs.8
@@ -64,6 +64,17 @@ but in other respects it is indistinguishable from the original.
 .Pp
 The
 .Nm
+utility supports mounting both directories and single files.
+Both
+.Ar target
+and
+.Ar mount_point
+must be the same type.
+Mounting directories to files or files to
+directories is not supported.
+.Pp
+The
+.Nm
 file system differs from a traditional
 loopback file system in two respects: it is implemented using
 a stackable layers techniques, and its
diff --git a/sbin/mount_nullfs/mount_nullfs.c b/sbin/mount_nullfs/mount_nullfs.c
index 77ec0991ea9b..55d7ac982f70 100644
--- a/sbin/mount_nullfs/mount_nullfs.c
+++ b/sbin/mount_nullfs/mount_nullfs.c
@@ -48,6 +48,7 @@ static const char rcsid[] =
 
 #include <sys/param.h>
 #include <sys/mount.h>
+#include <sys/stat.h>
 #include <sys/uio.h>
 
 #include <err.h>
@@ -61,6 +62,14 @@ static const char rcsid[] =
 
 static void	usage(void) __dead2;
 
+static int
+stat_realpath(const char *path, char *resolved, struct stat *sbp)
+{
+	if (realpath(path, resolved) == NULL || stat(resolved, sbp) != 0)
+		return (1);
+	return (0);
+}
+
 int
 main(int argc, char *argv[])
 {
@@ -71,6 +80,8 @@ main(int argc, char *argv[])
 	char errmsg[255];
 	int ch, iovlen;
 	char nullfs[] = "nullfs";
+	struct stat target_stat;
+	struct stat mountpoint_stat;
 
 	iov = NULL;
 	iovlen = 0;
@@ -98,10 +109,18 @@ main(int argc, char *argv[])
 		usage();
 
 	/* resolve target and mountpoint with realpath(3) */
-	if (checkpath(argv[0], target) != 0)
+	if (stat_realpath(argv[0], target, &target_stat) != 0)
 		err(EX_USAGE, "%s", target);
-	if (checkpath(argv[1], mountpoint) != 0)
+	if (stat_realpath(argv[1], mountpoint, &mountpoint_stat) != 0)
 		err(EX_USAGE, "%s", mountpoint);
+	if (!S_ISDIR(target_stat.st_mode) && !S_ISREG(target_stat.st_mode))
+		errx(EX_USAGE, "%s: must be either a file or directory",
+		    target);
+	if ((target_stat.st_mode & S_IFMT) !=
+	    (mountpoint_stat.st_mode & S_IFMT))
+		errx(EX_USAGE,
+		    "%s: must be same type as %s (file or directory)",
+		    mountpoint, target);
 
 	build_iovec(&iov, &iovlen, "fstype", nullfs, (size_t)-1);
 	build_iovec(&iov, &iovlen, "fspath", mountpoint, (size_t)-1);