Emulate closefrom() on macOS using proc_pidinfo().

This avoids relying on /dev/fd which may not exist in a chroot jail.
Adapted from a change in OpenSSH by likan_999.student AT sina.com

config.h.in

@@ -539,6 +539,9 @@
 /* Define to 1 if you have the <libintl.h> header file. */
 #undef HAVE_LIBINTL_H
 
+/* Define to 1 if you have the <libproc.h> header file. */
+#undef HAVE_LIBPROC_H
+
 /* Define to 1 if you have the <libutil.h> header file. */
 #undef HAVE_LIBUTIL_H
 
@@ -674,6 +677,9 @@
 /* Define to 1 if you have the <procfs.h> header file. */
 #undef HAVE_PROCFS_H
 
+/* Define to 1 if you have the `proc_pidinfo' function. */
+#undef HAVE_PROC_PIDINFO
+
 /* Define to 1 if you have the <project.h> header file. */
 #undef HAVE_PROJECT_H
 

configure

@@ -17851,6 +17851,24 @@ printf "%s\n" "#define HAVE_DECL_GETGROUPLIST_2 $ac_have_decl" >>confdefs.h
 
 fi
 
+done
+
+		# We use proc_pidinfo() to emulate closefrom() on macOS.
+		       for ac_header in libproc.h
+do :
+  ac_fn_c_check_header_compile "$LINENO" "libproc.h" "ac_cv_header_libproc_h" "$ac_includes_default"
+if test "x$ac_cv_header_libproc_h" = xyes
+then :
+  printf "%s\n" "#define HAVE_LIBPROC_H 1" >>confdefs.h
+ ac_fn_c_check_func "$LINENO" "proc_pidinfo" "ac_cv_func_proc_pidinfo"
+if test "x$ac_cv_func_proc_pidinfo" = xyes
+then :
+  printf "%s\n" "#define HAVE_PROC_PIDINFO 1" >>confdefs.h
+
+fi
+
+fi
+
 done
 
 		# We need to force a flat namespace to make libc

configure.ac

@@ -2205,6 +2205,9 @@ case "$host" in
 		# Undocumented API that dynamically allocates the groups.
 		AC_CHECK_FUNCS([getgrouplist_2], [AC_CHECK_DECLS([getgrouplist_2])])
 
+		# We use proc_pidinfo() to emulate closefrom() on macOS.
+		AC_CHECK_HEADERS([libproc.h], [AC_CHECK_FUNCS([proc_pidinfo])])
+
 		# We need to force a flat namespace to make libc
 		# symbol hooking work like it does on ELF.
 		AX_CHECK_LINK_FLAG([-Wl,-force_flat_namespace], [AX_APPEND_FLAG([-Wl,-force_flat_namespace], [SUDO_LDFLAGS])])

lib/util/closefrom.c

@@ -1,7 +1,7 @@
 /*
  * SPDX-License-Identifier: ISC
  *
- * Copyright (c) 2004-2005, 2007, 2010, 2012-2015, 2017-2018
+ * Copyright (c) 2004-2005, 2007, 2010, 2012-2015, 2017-2021
  *	Todd C. Miller <Todd.Miller@sudo.ws>
  *
  * Permission to use, copy, modify, and distribute this software for any
@@ -29,12 +29,16 @@
 #include <errno.h>
 #include <fcntl.h>
 #include <limits.h>
+#include <stdlib.h>
 #include <unistd.h>
 #ifdef HAVE_PSTAT_GETPROC
 # include <sys/pstat.h>
 #else
 # include <dirent.h>
 #endif
+#ifdef HAVE_LIBPROC_H
+# include <libproc.h>
+#endif
 
 #include "sudo_compat.h"
 #include "sudo_util.h"
@@ -44,6 +48,13 @@
 # define OPEN_MAX	256
 #endif
 
+/* Avoid potential libdispatch crash on macOS when we close its fds. */
+#ifdef __APPLE__
+# define closefrom_close(x)	fcntl((x), F_SETFD, FD_CLOEXEC)
+#else
+# define closefrom_close(x)	close(x)
+#endif
+
 /*
  * Close all file descriptors greater than or equal to lowfd.
  * This is the expensive (fallback) method.
@@ -69,12 +80,7 @@ closefrom_fallback(int lowfd)
 	maxfd = INT_MAX;
 
     for (fd = lowfd; fd < maxfd; fd++) {
-#ifdef __APPLE__
-	/* Avoid potential libdispatch crash when we close its fds. */
-	(void) fcntl((int) fd, F_SETFD, FD_CLOEXEC);
-#else
-	(void) close((int) fd);
-#endif
+	(void)closefrom_close((int)fd);
     }
 }
 
@@ -91,12 +97,45 @@ sudo_closefrom(int lowfd)
     const char *path;
     DIR *dirp;
 #endif
+#if defined(HAVE_PROC_PIDINFO)
+    struct proc_fdinfo *buf = NULL;
+    const pid_t pid = getpid();
+    int i, n, len;
+#endif
 
     /* Try the fast method first, if possible. */
 #if defined(HAVE_FCNTL_CLOSEM)
     if (fcntl(lowfd, F_CLOSEM, 0) != -1)
 	return;
-#endif
+#elif defined(HAVE_PROC_PIDINFO)
+    len = proc_pidinfo(pid, PROC_PIDLISTFDS, 0, NULL, 0);
+    switch (len) {
+    case 0:
+	/* No open files. */
+	return;
+    case -1:
+	/* Fall back on other methods. */
+	break;
+    default:
+	/* Allocate space for 4 extra fds to leave some wiggle room. */
+	buf = malloc(len + (PROC_PIDLISTFD_SIZE * 4));
+	if (buf == NULL)
+	    break;
+	n = proc_pidinfo(pid, PROC_PIDLISTFDS, 0, buf, len);
+	if (n == -1 || n > len) {
+	    free(buf);
+	    break;
+	}
+	n /= PROC_PIDLISTFD_SIZE;
+	for (i = 0; i < n; i++) {
+	    if (buf[i].proc_fd >= lowfd) {
+		(void)closefrom_close(buf[i].proc_fd);
+	    }
+	}
+	free(buf);
+	return;
+    }
+#endif /* HAVE_PROC_PIDINFO */
 #if defined(HAVE_PSTAT_GETPROC)
     /*
      * EOVERFLOW is not a fatal error for the fields we use.
@@ -107,7 +146,7 @@ sudo_closefrom(int lowfd)
 	int fd;
 
 	for (fd = lowfd; fd <= pst.pst_highestfd; fd++)
-	    (void) close(fd);
+	    (void)closefrom_close(fd);
 	return;
     }
 #elif defined(HAVE_DIRFD)
@@ -123,15 +162,10 @@ sudo_closefrom(int lowfd)
 	    const char *errstr;
 	    int fd = sudo_strtonum(dent->d_name, lowfd, INT_MAX, &errstr);
 	    if (errstr == NULL && fd != dirfd(dirp)) {
-# ifdef __APPLE__
-		/* Avoid potential libdispatch crash when we close its fds. */
-		(void) fcntl(fd, F_SETFD, FD_CLOEXEC);
-# else
-		(void) close(fd);
-# endif
+		(void)closefrom_close(fd);
 	    }
 	}
-	(void) closedir(dirp);
+	(void)closedir(dirp);
 	return;
     }
 #endif /* HAVE_DIRFD */