Add scandirat(3); from freebsd

To be used in httpd(8) shortly to prevent toctu issues.

This makes __fdopendir internally accessible to avoid unnecessary
syscalls in scandirat(3). Suggested & diff by guenther

suggested by & OK millert
tweak & OK guenther
OK tb, jca

This rides the libc crank.

5 files changed, 81 insertions, 12 deletions

diff --git a/lib/libc/Symbols.list b/lib/libc/Symbols.list
index 251760f812e..b1e7e916bbc 100644
--- a/lib/libc/Symbols.list
+++ b/lib/libc/Symbols.list
@@ -750,6 +750,7 @@ readdir_r
 readpassphrase
 rewinddir
 scandir
+scandirat
 seekdir
 setclasscontext
 setdomainname
diff --git a/lib/libc/gen/opendir.c b/lib/libc/gen/opendir.c
index 71d30da9386..ef198924efb 100644
--- a/lib/libc/gen/opendir.c
+++ b/lib/libc/gen/opendir.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: opendir.c,v 1.30 2016/09/21 04:38:56 guenther Exp $ */
+/*	$OpenBSD: opendir.c,v 1.31 2024/04/15 15:47:58 florian Exp $ */
 /*
  * Copyright (c) 1983, 1993
  *	The Regents of the University of California.  All rights reserved.
@@ -39,7 +39,6 @@
 
 #include "telldir.h"
 
-static DIR *__fdopendir(int fd);
 
 /*
  * Open a directory specified by name.
@@ -89,7 +88,7 @@ fdopendir(int fd)
 }
 DEF_WEAK(fdopendir);
 
-static DIR *
+DIR *
 __fdopendir(int fd)
 {
 	DIR *dirp;
diff --git a/lib/libc/gen/scandir.3 b/lib/libc/gen/scandir.3
index 50033134303..fda3a82f702 100644
--- a/lib/libc/gen/scandir.3
+++ b/lib/libc/gen/scandir.3
@@ -1,4 +1,4 @@
-.\"	$OpenBSD: scandir.3,v 1.16 2021/06/17 18:18:15 jmc Exp $
+.\"	$OpenBSD: scandir.3,v 1.17 2024/04/15 15:47:58 florian Exp $
 .\"
 .\" Copyright (c) 1983, 1991, 1993
 .\"	The Regents of the University of California.  All rights reserved.
@@ -27,11 +27,12 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.Dd $Mdocdate: June 17 2021 $
+.Dd $Mdocdate: April 15 2024 $
 .Dt SCANDIR 3
 .Os
 .Sh NAME
 .Nm scandir ,
+.Nm scandirat ,
 .Nm alphasort
 .Nd scan a directory
 .Sh SYNOPSIS
@@ -45,6 +46,14 @@
 .Fa "int (*compar)(const struct dirent **, const struct dirent **)"
 .Fc
 .Ft int
+.Fo scandirat
+.Fa "int dirfd"
+.Fa "const char *dirname"
+.Fa "struct dirent ***namelist"
+.Fa "int (*select)(const struct dirent *)"
+.Fa "int (*compar)(const struct dirent **, const struct dirent **)"
+.Fc
+.Ft int
 .Fn alphasort "const struct dirent **d1" "const struct dirent **d2"
 .Sh DESCRIPTION
 The
@@ -91,6 +100,30 @@ parameter to sort the array alphabetically.
 The memory allocated for the array can be deallocated with
 .Xr free 3 ,
 by freeing each pointer in the array and then the array itself.
+.Pp
+The
+.Fn scandirat
+function is similar to
+.Fn scandir ,
+but takes an additional
+.Fa dirfd
+argument.
+If
+.Fa dirname
+is relative,
+.Fa dirfd
+must be a valid file descriptor referencing a directory, in which case the
+.Fa dirname
+lookup is performed relative to the directory referenced by
+.Fa dirfd .
+If
+.Fa dirfd
+has the special value
+.Va AT_FDCWD ,
+then the current process directory is used as the base for relative lookups.
+See
+.Xr openat 2
+for additional details.
 .Sh DIAGNOSTICS
 Returns \-1 if the directory cannot be opened for reading or if
 .Xr malloc 3
diff --git a/lib/libc/gen/scandir.c b/lib/libc/gen/scandir.c
index f767ca503fa..5d62fb7a089 100644
--- a/lib/libc/gen/scandir.c
+++ b/lib/libc/gen/scandir.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: scandir.c,v 1.22 2024/04/14 11:21:08 florian Exp $ */
+/*	$OpenBSD: scandir.c,v 1.23 2024/04/15 15:47:58 florian Exp $ */
 /*
  * Copyright (c) 1983, 1993
  *	The Regents of the University of California.  All rights reserved.
@@ -39,9 +39,11 @@
 #include <sys/stat.h>
 #include <dirent.h>
 #include <errno.h>
+#include <fcntl.h>
 #include <stdint.h>
 #include <stdlib.h>
 #include <string.h>
+#include <unistd.h>
 #include "telldir.h"
 
 #define MAXIMUM(a, b)	(((a) > (b)) ? (a) : (b))
@@ -57,8 +59,8 @@
 	((sizeof(struct dirent) - sizeof(dp)->d_name) +			\
 	    (((dp)->d_namlen + 1 + 3) &~ 3))
 
-int
-scandir(const char *dirname, struct dirent ***namelist,
+static int
+scandir_dirp(DIR *dirp, struct dirent ***namelist,
     int (*select)(const struct dirent *),
     int (*dcomp)(const struct dirent **, const struct dirent **))
 {
@@ -66,10 +68,7 @@ scandir(const char *dirname, struct dirent ***namelist,
 	size_t nitems = 0;
 	struct stat stb;
 	long arraysz;
-	DIR *dirp;
 
-	if ((dirp = opendir(dirname)) == NULL)
-		return (-1);
 	if (fstat(dirp->dd_fd, &stb) == -1)
 		goto fail;
 
@@ -140,6 +139,38 @@ fail:
 	return (-1);
 }
 
+int
+scandir(const char *dirname, struct dirent ***namelist,
+    int (*select)(const struct dirent *),
+    int (*dcomp)(const struct dirent **, const struct dirent **))
+{
+	DIR *dirp;
+
+	if ((dirp = opendir(dirname)) == NULL)
+		return (-1);
+
+	return (scandir_dirp(dirp, namelist, select, dcomp));
+}
+
+int
+scandirat(int dirfd, const char *dirname, struct dirent ***namelist,
+    int (*select)(const struct dirent *),
+    int (*dcomp)(const struct dirent **, const struct dirent **))
+{
+	DIR *dirp;
+	int fd;
+
+	fd = HIDDEN(openat)(dirfd, dirname, O_RDONLY | O_DIRECTORY | O_CLOEXEC);
+	if (fd == -1)
+		return (-1);
+	dirp = __fdopendir(fd);
+	if (dirp == NULL) {
+		HIDDEN(close)(fd);
+		return (-1);
+	}
+	return (scandir_dirp(dirp, namelist, select, dcomp));
+}
+
 /*
  * Alphabetic order comparison routine for those who want it.
  */
diff --git a/lib/libc/hidden/dirent.h b/lib/libc/hidden/dirent.h
index 1e8398291c8..e683252e016 100644
--- a/lib/libc/hidden/dirent.h
+++ b/lib/libc/hidden/dirent.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: dirent.h,v 1.1 2015/09/12 13:34:22 guenther Exp $	*/
+/*	$OpenBSD: dirent.h,v 1.2 2024/04/15 15:47:58 florian Exp $	*/
 /*
  * Copyright (c) 2015 Philip Guenther <guenther@openbsd.org>
  *
@@ -20,6 +20,10 @@
 
 #include_next <dirent.h>
 
+__BEGIN_HIDDEN_DECLS
+DIR	*__fdopendir(int fd);
+__END_HIDDEN_DECLS
+
 PROTO_DEPRECATED(alphasort);
 PROTO_NORMAL(closedir);
 PROTO_NORMAL(dirfd);
@@ -30,6 +34,7 @@ PROTO_NORMAL(readdir);
 PROTO_DEPRECATED(readdir_r);
 PROTO_DEPRECATED(rewinddir);
 PROTO_DEPRECATED(scandir);
+PROTO_DEPRECATED(scandirat);
 PROTO_NORMAL(seekdir);
 PROTO_NORMAL(telldir);