Fix a TOCTOU and symlink attack in netd.

Bug: 7530471
Change-Id: I3b0a38a203bdeba6c492a54fded056a16992e34e

diff --git a/SoftapController.cpp b/SoftapController.cpp
index ce41544..3d69142 100644 (file)
--- a/SoftapController.cpp
+++ b/SoftapController.cpp
@@ -310,7 +310,7 @@ int SoftapController::setSoftap(int argc, char *argv[]) {
         asprintf(&fbuf, "%s", wbuf);
     }
 
-    fd = open(HOSTAPD_CONF_FILE, O_CREAT | O_TRUNC | O_WRONLY, 0660);
+    fd = open(HOSTAPD_CONF_FILE, O_CREAT | O_TRUNC | O_WRONLY | O_NOFOLLOW, 0660);
     if (fd < 0) {
         ALOGE("Cannot update \"%s\": %s", HOSTAPD_CONF_FILE, strerror(errno));
         free(wbuf);
@@ -321,25 +321,27 @@ int SoftapController::setSoftap(int argc, char *argv[]) {
         ALOGE("Cannot write to \"%s\": %s", HOSTAPD_CONF_FILE, strerror(errno));
         ret = -1;
     }
-    close(fd);
     free(wbuf);
     free(fbuf);
 
     /* Note: apparently open can fail to set permissions correctly at times */
-    if (chmod(HOSTAPD_CONF_FILE, 0660) < 0) {
+    if (fchmod(fd, 0660) < 0) {
         ALOGE("Error changing permissions of %s to 0660: %s",
                 HOSTAPD_CONF_FILE, strerror(errno));
+        close(fd);
         unlink(HOSTAPD_CONF_FILE);
         return -1;
     }
 
-    if (chown(HOSTAPD_CONF_FILE, AID_SYSTEM, AID_WIFI) < 0) {
+    if (fchown(fd, AID_SYSTEM, AID_WIFI) < 0) {
         ALOGE("Error changing group ownership of %s to %d: %s",
                 HOSTAPD_CONF_FILE, AID_WIFI, strerror(errno));
+        close(fd);
         unlink(HOSTAPD_CONF_FILE);
         return -1;
     }
 
+    close(fd);
 #else
     /* Create command line */
     i = addParam(i, "ASCII_CMD", "AP_CFG");