Add special utimensat(2) flag to allow setting explicit birthtime

Some applications over SMB protocol may inadvertently initialize
the inode birthtime to 1980 due to non-standard FreeBSD setutimes()
behavior, which applies the mtime timespec to birthtime if it is
older than existing birthtime. It is not possible to fix this using
existing calls to utimensat(2) or futimens(2). Additionally,
SMB clients, may attempt to set birthtime to a date more recent
than the mtime.

This PR adds a utimensat(2) flag that may be used to
specify that  an array of three timespecs are being provided rather
than two. In this case the third timespec struct specifies the
birthtime to be set.

sys/kern/vfs_syscalls.c

@@ -98,7 +98,7 @@ static int kern_chflagsat(struct thread *td, int fd, const char *path,
 static int setfflags(struct thread *td, struct vnode *, u_long);
 static int getutimes(const struct timeval *, enum uio_seg, struct timespec *);
 static int getutimens(const struct timespec *, enum uio_seg,
-    struct timespec *, int *);
+    struct timespec *, bool, int *);
 static int setutimes(struct thread *td, struct vnode *,
     const struct timespec *, int, int);
 static int vn_access(struct vnode *vp, int user_flags, struct ucred *cred,
@@ -3117,40 +3117,46 @@ getutimes(const struct timeval *usrtvp, enum uio_seg tvpseg,
 #define	UTIMENS_EXIT	0x2
 static int
 getutimens(const struct timespec *usrtsp, enum uio_seg tspseg,
-    struct timespec *tsp, int *retflags)
+    struct timespec *tsp, bool get_btime, int *retflags)
 {
 	struct timespec tsnow;
-	int error;
+	int error, i;
+	int cnt = get_btime ? 3 : 2;
+	int flags = UTIMENS_NULL | UTIMENS_EXIT;
 
 	vfs_timestamp(&tsnow);
 	*retflags = 0;
 	if (usrtsp == NULL) {
-		tsp[0] = tsnow;
-		tsp[1] = tsnow;
+		for (i = 0; i < cnt; i++)
+			tsp[i] = tsnow;
+
 		*retflags |= UTIMENS_NULL;
 		return (0);
 	}
 	if (tspseg == UIO_SYSSPACE) {
-		tsp[0] = usrtsp[0];
-		tsp[1] = usrtsp[1];
-	} else if ((error = copyin(usrtsp, tsp, sizeof(*tsp) * 2)) != 0)
+		for (i = 0; i < cnt; i++)
+			tsp[i] = usrtsp[i];
+	} else if ((error = copyin(usrtsp, tsp, sizeof(*tsp) * cnt)) != 0)
 		return (error);
-	if (tsp[0].tv_nsec == UTIME_OMIT && tsp[1].tv_nsec == UTIME_OMIT)
-		*retflags |= UTIMENS_EXIT;
-	if (tsp[0].tv_nsec == UTIME_NOW && tsp[1].tv_nsec == UTIME_NOW)
-		*retflags |= UTIMENS_NULL;
-	if (tsp[0].tv_nsec == UTIME_OMIT)
-		tsp[0].tv_sec = VNOVAL;
-	else if (tsp[0].tv_nsec == UTIME_NOW)
-		tsp[0] = tsnow;
-	else if (tsp[0].tv_nsec < 0 || tsp[0].tv_nsec >= 1000000000L)
-		return (EINVAL);
-	if (tsp[1].tv_nsec == UTIME_OMIT)
-		tsp[1].tv_sec = VNOVAL;
-	else if (tsp[1].tv_nsec == UTIME_NOW)
-		tsp[1] = tsnow;
-	else if (tsp[1].tv_nsec < 0 || tsp[1].tv_nsec >= 1000000000L)
-		return (EINVAL);
+
+	for (i = 0; i < cnt; i++) {
+		switch(tsp[i].tv_nsec) {
+		case UTIME_OMIT:
+			tsp[i].tv_sec = VNOVAL;
+			flags &= ~UTIMENS_NULL;
+			break;
+		case UTIME_NOW:
+			tsp[i] = tsnow;
+			flags &= ~UTIMENS_EXIT;
+			break;
+		default:
+			if (tsp[i].tv_nsec < 0 || tsp[i].tv_nsec >= 1000000000L)
+				return (EINVAL);
+
+			flags = 0;
+		}
+	}
+	*retflags = flags;
 
 	return (0);
 }
@@ -3346,7 +3352,7 @@ kern_futimens(struct thread *td, int fd, struct timespec *tptr,
 	int error, flags;
 
 	AUDIT_ARG_FD(fd);
-	error = getutimens(tptr, tptrseg, ts, &flags);
+	error = getutimens(tptr, tptrseg, ts, false, &flags);
 	if (error != 0)
 		return (error);
 	if (flags & UTIMENS_EXIT)
@@ -3380,14 +3386,17 @@ kern_utimensat(struct thread *td, int fd, const char *path,
     int flag)
 {
 	struct nameidata nd;
-	struct timespec ts[2];
+	struct timespec ts[3];
 	int error, flags;
+	bool get_btime = flag & AT_UTIMENSAT_BTIME;
+
+	flag &= ~AT_UTIMENSAT_BTIME;
 
 	if ((flag & ~(AT_SYMLINK_NOFOLLOW | AT_RESOLVE_BENEATH |
 	    AT_EMPTY_PATH)) != 0)
 		return (EINVAL);
 
-	if ((error = getutimens(tptr, tptrseg, ts, &flags)) != 0)
+	if ((error = getutimens(tptr, tptrseg, ts, get_btime, &flags)) != 0)
 		return (error);
 	NDINIT_ATRIGHTS(&nd, LOOKUP, at2cnpflags(flag, AT_SYMLINK_NOFOLLOW |
 	    AT_RESOLVE_BENEATH | AT_EMPTY_PATH) | AUDITVNODE1,
@@ -3402,7 +3411,8 @@ kern_utimensat(struct thread *td, int fd, const char *path,
 	 */
 	NDFREE_NOTHING(&nd);
 	if ((flags & UTIMENS_EXIT) == 0)
-		error = setutimes(td, nd.ni_vp, ts, 2, flags & UTIMENS_NULL);
+		error = setutimes(td, nd.ni_vp, ts, get_btime ? 3 : 2,
+		    flags & UTIMENS_NULL);
 	vrele(nd.ni_vp);
 	return (error);
 }

sys/sys/fcntl.h

@@ -229,6 +229,7 @@ typedef	__pid_t		pid_t;
 #endif	/* __POSIX_VISIBLE >= 200809 */
 #if __BSD_VISIBLE
 /* #define AT_UNUSED1		0x1000 *//* Was AT_BENEATH */
+#define	AT_UTIMENSAT_BTIME	0x1000
 #define	AT_RESOLVE_BENEATH	0x2000	/* Do not allow name resolution
 					   to walk out of dirfd */
 #define	AT_EMPTY_PATH		0x4000	/* Operate on dirfd if path is empty */