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.

diff --git a/src/conf.c b/src/conf.c
index e67c7ac1ff934bd6f61cff2109861622e8e236e7..f64fb22127ac018c5a54459b5b64bd8a70599238 100644 (file)
--- a/src/conf.c
+++ b/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);
-       }
-
-       maxlen = size;
-       idx = line;
-       *idx = 0;
-
-       for(;;) {
-               errno = 0;
-               p = fgets(idx, maxlen, fp);
+       p = fgets(buf, buflen, fp);
 
-               if(!p) {                                /* EOF or error */
-                       if(feof(fp))
-                               break;
+       if(!p)
+               return NULL;
 
-                       /* otherwise: error; let the calling function print an error message if applicable */
-                       free(line);
-                       return NULL;
-               }
+       newline = strchr(p, '\n');
 
-               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(!newline)
+               return NULL;
 
-       if(buf && buflen) {
-               *buflen = size;
-               *buf = line;
-       }
+       *newline = '\0';        /* kill newline */
+       if(newline > p && newline[-1] == '\r')  /* and carriage return if necessary */
+               newline[-1] = '\0';
 
-       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;
 }
 

diff --git a/src/conf.h b/src/conf.h
index be49733698a6df5a788b44a80b18275c369a95f1..dae4eab8ecdeb49af26873f30576b945a475a89c 100644 (file)
--- a/src/conf.h
+++ b/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 *);