Simplify reading lines from configuration files.

Instead of allocating storage for each line read, we now read into fixed-size
buffers on the stack. This fixes a case where a malformed configuration file
could crash tinc.

src/conf.c

@@ -26,6 +26,7 @@
 #include "conf.h"
 #include "logger.h"
 #include "netutl.h"				/* for str2address */
+#include "protocol.h"
 #include "utils.h"				/* for cp */
 #include "xalloc.h"
 
@@ -206,111 +207,60 @@ bool get_config_subnet(const config_t *cfg, subnet_t ** result) {
 }
 
 /*
-  Read exactly one line and strip the trailing newline if any.  If the
-  file was on EOF, return NULL. Otherwise, return all the data in a
-  dynamically allocated buffer.
-
-  If line is non-NULL, it will be used as an initial buffer, to avoid
-  unnecessary mallocing each time this function is called.  If buf is
-  given, and buf needs to be expanded, the var pointed to by buflen
-  will be increased.
+  Read exactly one line and strip the trailing newline if any.
 */
-static char *readline(FILE * fp, char **buf, size_t *buflen) {
+static char *readline(FILE * fp, char *buf, size_t buflen) {
 	char *newline = NULL;
 	char *p;
-	char *line;					/* The array that contains everything that has been read so far */
-	char *idx;					/* Read into this pointer, which points to an offset within line */
-	size_t size, newsize;		/* The size of the current array pointed to by line */
-	size_t maxlen;				/* Maximum number of characters that may be read with fgets.  This is newsize - oldsize. */
 
 	if(feof(fp))
 		return NULL;
 
-	if(buf && buflen) {
-		size = *buflen;
-		line = *buf;
-	} else {
-		size = 100;
-		line = xmalloc(size);
-	}
+	p = fgets(buf, buflen, fp);
 
-	maxlen = size;
-	idx = line;
-	*idx = 0;
+	if(!p)
+		return NULL;
 
-	for(;;) {
-		errno = 0;
-		p = fgets(idx, maxlen, fp);
+	newline = strchr(p, '\n');
 
-		if(!p) {				/* EOF or error */
-			if(feof(fp))
-				break;
+	if(!newline)
+		return NULL;
 
-			/* otherwise: error; let the calling function print an error message if applicable */
-			free(line);
-			return NULL;
-		}
+	*newline = '\0';	/* kill newline */
+	if(newline > p && newline[-1] == '\r')	/* and carriage return if necessary */
+		newline[-1] = '\0';
 
-		newline = strchr(p, '\n');
-
-		if(!newline) {			/* We haven't yet read everything to the end of the line */
-			newsize = size << 1;
-			line = xrealloc(line, newsize);
-			idx = &line[size - 1];
-			maxlen = newsize - size + 1;
-			size = newsize;
-		} else {
-			*newline = '\0';	/* kill newline */
-			if(newline > p && newline[-1] == '\r')	/* and carriage return if necessary */
-				newline[-1] = '\0';
-			break;				/* yay */
-		}
-	}
-
-	if(buf && buflen) {
-		*buflen = size;
-		*buf = line;
-	}
-
-	return line;
+	return buf;
 }
 
 /*
   Parse a configuration file and put the results in the configuration tree
   starting at *base.
 */
-int read_config_file(avl_tree_t *config_tree, const char *fname) {
-	int err = -2;				/* Parse error */
+bool read_config_file(avl_tree_t *config_tree, const char *fname) {
 	FILE *fp;
-	char *buffer, *line;
+	char buffer[MAX_STRING_SIZE];
+	char *line;
 	char *variable, *value, *eol;
 	int lineno = 0;
 	int len;
 	bool ignore = false;
 	config_t *cfg;
-	size_t bufsize;
+	bool result = false;
 
 	fp = fopen(fname, "r");
 
 	if(!fp) {
-		logger(LOG_ERR, "Cannot open config file %s: %s", fname,
-			   strerror(errno));
-		return -3;
+		logger(LOG_ERR, "Cannot open config file %s: %s", fname, strerror(errno));
+		return false;
 	}
 
-	bufsize = 100;
-	buffer = xmalloc(bufsize);
-
 	for(;;) {
-		if(feof(fp)) {
-			err = 0;
-			break;
-		}
-
-		line = readline(fp, &buffer, &bufsize);
+		line = readline(fp, buffer, sizeof buffer);
 
 		if(!line) {
-			err = -1;
+			if(feof(fp))
+				result = true;
 			break;
 		}
 
@@ -361,46 +311,46 @@ int read_config_file(avl_tree_t *config_tree, const char *fname) {
 		config_add(config_tree, cfg);
 	}
 
-	free(buffer);
 	fclose(fp);
 
-	return err;
+	return result;
 }
 
 bool read_server_config() {
 	char *fname;
-	int x;
+	bool x;
 
 	xasprintf(&fname, "%s/tinc.conf", confbase);
 	x = read_config_file(config_tree, fname);
 
-	if(x == -1) {				/* System error: complain */
+	if(!x) {				/* System error: complain */
 		logger(LOG_ERR, "Failed to read `%s': %s", fname, strerror(errno));
 	}
 
 	free(fname);
 
-	return x == 0;
+	return x;
 }
 
 FILE *ask_and_open(const char *filename, const char *what) {
 	FILE *r;
 	char *directory;
-	char *fn;
+	char line[PATH_MAX];
+	const char *fn;
 
 	/* Check stdin and stdout */
 	if(!isatty(0) || !isatty(1)) {
 		/* Argh, they are running us from a script or something.  Write
 		   the files to the current directory and let them burn in hell
 		   for ever. */
-		fn = xstrdup(filename);
+		fn = filename;
 	} else {
 		/* Ask for a file and/or directory name. */
 		fprintf(stdout, "Please enter a file to save %s to [%s]: ",
 				what, filename);
 		fflush(stdout);
 
-		fn = readline(stdin, NULL, NULL);
+		fn = readline(stdin, line, sizeof line);
 
 		if(!fn) {
 			fprintf(stderr, "Error while reading stdin: %s\n",
@@ -410,7 +360,7 @@ FILE *ask_and_open(const char *filename, const char *what) {
 
 		if(!strlen(fn))
 			/* User just pressed enter. */
-			fn = xstrdup(filename);
+			fn = filename;
 	}
 
 #ifdef HAVE_MINGW
@@ -423,7 +373,6 @@ FILE *ask_and_open(const char *filename, const char *what) {
 
 		directory = get_current_dir_name();
 		xasprintf(&p, "%s/%s", directory, fn);
-		free(fn);
 		free(directory);
 		fn = p;
 	}
@@ -437,12 +386,9 @@ FILE *ask_and_open(const char *filename, const char *what) {
 	if(!r) {
 		fprintf(stderr, "Error opening file `%s': %s\n",
 				fn, strerror(errno));
-		free(fn);
 		return NULL;
 	}
 
-	free(fn);
-
 	return r;
 }
 

src/conf.h

@@ -54,7 +54,7 @@ extern bool get_config_string(const config_t *, char **);
 extern bool get_config_address(const config_t *, struct addrinfo **);
 extern bool get_config_subnet(const config_t *, struct subnet_t **);
 
-extern int read_config_file(avl_tree_t *, const char *);
+extern bool read_config_file(avl_tree_t *, const char *);
 extern bool read_server_config(void);
 extern FILE *ask_and_open(const char *, const char *);
 extern bool is_safe_path(const char *);