libreplace: Add a closefrom() implementation

There is closefrom in some BSDs, but Linux ships this only as part
of libbsd.  Add a new implementation of it in libreplace. The one in
libbsd of jessie and upstream differ and it has for example optimizations
for FreeBSD, but it gets some of the array calculations slightly wrong
from my point of view. If you want those, use libbsd. This replacement
is optimized on Linux only looking at /proc/self/fd/, everything else
would do the OPEN_MAX brute force fallback.

Signed-off-by: Volker Lendecke <vl@samba.org>

lib/replace/closefrom.c

@@ -0,0 +1,138 @@
+/*
+ * Unix SMB/CIFS implementation.
+ * Samba utility functions
+ * Copyright (C) Volker Lendecke 2016
+ *
+ *   ** NOTE! The following LGPL license applies to the replace
+ *   ** library. This does NOT imply that all of Samba is released
+ *   ** under the LGPL
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 3 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Library General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "replace.h"
+#include <dirent.h>
+#include <unistd.h>
+#include <limits.h>
+
+static int closefrom_sysconf(int lower)
+{
+	long max_files, fd;
+
+	max_files = sysconf(_SC_OPEN_MAX);
+	if (max_files == -1) {
+		max_files = 65536;
+	}
+
+	for (fd=lower; fd<max_files; fd++) {
+		close(fd);
+	}
+
+	return 0;
+}
+
+static int closefrom_procfs(int lower)
+{
+	DIR *dirp;
+	int dir_fd;
+	struct dirent *dp;
+	int *fds = NULL;
+	size_t num_fds = 0;
+	size_t fd_array_size = 0;
+	size_t i;
+	int ret = ENOMEM;
+
+	dirp = opendir("/proc/self/fd");
+	if (dirp == 0) {
+		return errno;
+	}
+
+	dir_fd = dirfd(dirp);
+	if (dir_fd == -1) {
+		ret = errno;
+		goto fail;
+	}
+
+	while ((dp = readdir(dirp)) != NULL) {
+		char *endptr;
+		unsigned long long fd;
+
+		errno = 0;
+
+		fd = strtoull(dp->d_name, &endptr, 10);
+		if ((fd == 0) && (errno == EINVAL)) {
+			continue;
+		}
+		if ((fd == ULLONG_MAX) && (errno == ERANGE)) {
+			continue;
+		}
+		if (*endptr != '\0') {
+			continue;
+		}
+		if (fd == dir_fd) {
+			continue;
+		}
+		if (fd > INT_MAX) {
+			continue;
+		}
+		if (fd < lower) {
+			continue;
+		}
+
+		if (num_fds >= (fd_array_size / sizeof(int))) {
+			void *tmp;
+
+			if (fd_array_size == 0) {
+				fd_array_size = 16 * sizeof(int);
+			} else {
+				if (fd_array_size + fd_array_size <
+				    fd_array_size) {
+					/* overflow */
+					goto fail;
+				}
+				fd_array_size = fd_array_size + fd_array_size;
+			}
+
+			tmp = realloc(fds, fd_array_size);
+			if (tmp == NULL) {
+				goto fail;
+			}
+			fds = tmp;
+		}
+
+		fds[num_fds++] = fd;
+	}
+
+	for (i=0; i<num_fds; i++) {
+		close(fds[i]);
+	}
+
+	ret = 0;
+fail:
+	closedir(dirp);
+	free(fds);
+	return ret;
+}
+
+int rep_closefrom(int lower)
+{
+	int ret;
+
+	ret = closefrom_procfs(lower);
+	if (ret == 0) {
+		return 0;
+	}
+
+	return closefrom_sysconf(lower);
+}

lib/replace/replace.h

@@ -247,6 +247,12 @@ size_t rep_strlcpy(char *d, const char *s, size_t bufsize);
 size_t rep_strlcat(char *d, const char *s, size_t bufsize);
 #endif
 
+#ifndef HAVE_CLOSEFROM
+#define closefrom rep_closefrom
+int rep_closefrom(int lower);
+#endif
+
+
 #if (defined(BROKEN_STRNDUP) || !defined(HAVE_STRNDUP))
 #undef HAVE_STRNDUP
 #define strndup rep_strndup

lib/replace/wscript

@@ -257,6 +257,9 @@ def configure(conf):
     if not conf.CHECK_FUNCS_IN('setproctitle', 'setproctitle', headers='setproctitle.h'):
         conf.CHECK_FUNCS_IN('setproctitle', 'bsd', headers='sys/types.h bsd/unistd.h')
 
+    if not conf.CHECK_FUNCS('closefrom'):
+        conf.CHECK_FUNCS_IN('closefrom', 'bsd', headers='bsd/unistd.h')
+
     conf.CHECK_CODE('''
                 struct ucred cred;
                 socklen_t cred_len;
@@ -683,6 +686,9 @@ def build(bld):
     if not bld.CONFIG_SET('HAVE_GETXATTR') or bld.CONFIG_SET('XATTR_ADDITIONAL_OPTIONS'):
                                                  REPLACE_SOURCE += ' xattr.c'
 
+    if not bld.CONFIG_SET('HAVE_CLOSEFROM'):
+        REPLACE_SOURCE += ' closefrom.c'
+
     bld.SAMBA_LIBRARY('replace',
                       source=REPLACE_SOURCE,
                       group='base_libraries',