o added safeopen.c,h: a somewhat safer interface to open.

src/common/safeopen.c

+/* $Id$ */
+
+/* safer interface to open()
+ */
+
+
+#if HAVE_CONFIG_H
+#  include <config.h>
+#endif 
+
+#if HAVE_UNISTD_H
+#  include <unistd.h>
+#endif
+#include <stdio.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+
+#include "safeopen.h"
+
+FILE * safeopen(const char *path, const char *mode, int flags)
+{
+	int fd;
+	int oflags;
+	struct stat fb1, fb2;
+
+	if(mode[0] == 'w') {
+		oflags = O_WRONLY;
+	} else if (mode[0] == 'a') {
+		oflags = O_CREAT | O_WRONLY | O_APPEND;
+	} else
+		oflags = O_RDONLY;
+
+	oflags |= !(flags & SAFEOPEN_NOCREATE)   ? O_CREAT : 0;
+	oflags |= (flags & SAFEOPEN_CREATE_ONLY) ? O_EXCL  : 0;
+
+	if ((fd = open(path, oflags, S_IRUSR|S_IWUSR)) < 0)
+		return NULL;
+
+	if (!(flags & SAFEOPEN_LINK_OK)) {
+		lstat(path, &fb1);
+		fstat(fd,   &fb2);
+
+		if (fb2.st_ino != fb1.st_ino) {
+			fprintf(stderr, "safeopen(): refusing to open `%s', " 
+					"which is a soft link\n", path);
+			close(fd);
+			return NULL;
+		}
+	}
+
+	return fdopen(fd, mode);
+
+}

src/common/safeopen.h

+/* $Id$ */
+
+/* safer interface to open():
+ *
+ */
+
+#ifndef _SAFEOPEN_H
+#define _SAFEOPEN_H
+
+/* safeopen flags:
+ *
+ * default is to create if needed, and fail if path is a soft link
+ */
+#define SAFEOPEN_LINK_OK	(1<<0) 	/* do not check for soft link	*/
+#define SAFEOPEN_CREATE_ONLY	(1<<1)  /* create, fail if file exists	*/
+#define SAFEOPEN_NOCREATE	(1<<2)	/* fail if file doesn't exist	*/
+
+/* open a file for read, write, or append
+ * perform some simple sanity checks on file and return stream pointer
+ */
+FILE *safeopen(const char *path, const char *mode, int flags);
+
+#endif /* _SAFEOPEN_H */