Fix buffer overflow in mount path parsing

In the mount monitor we parse mount points from /proc/self/mountinfo and
/proc/swaps. Ensure that we don't overflow the buffers on platforms where mount
paths could be longer than PATH_MAX (unknown if that can actually happen), as
at least the mount paths for hotpluggable devices are somewhat user-controlled.

Thanks to Florian Weimer for discovering this bug, and to David Zeuthen
for his initial patch!

CVE-2014-0004

1 files changed, 18 insertions, 8 deletions

diff --git a/src/udisksmountmonitor.c b/src/udisksmountmonitor.c
index 8af1028..e7097fa 100644
--- a/src/udisksmountmonitor.c
+++ b/src/udisksmountmonitor.c
@@ -38,6 +38,11 @@
 #include "udisksmount.h"
 #include "udisksprivate.h"
 
+/* build a %Ns format string macro with N == PATH_MAX */
+#define xstr(s) str(s)
+#define str(s) #s
+#define PATH_MAX_FMT "%" xstr(PATH_MAX) "s"
+
 /**
  * SECTION:udisksmountmonitor
  * @title: UDisksMountMonitor
@@ -416,8 +421,8 @@ udisks_mount_monitor_get_mountinfo (UDisksMountMonitor  *monitor,
       guint mount_id;
       guint parent_id;
       guint major, minor;
-      gchar encoded_root[PATH_MAX];
-      gchar encoded_mount_point[PATH_MAX];
+      gchar encoded_root[PATH_MAX + 1];
+      gchar encoded_mount_point[PATH_MAX + 1];
       gchar *mount_point;
       dev_t dev;
 
@@ -425,7 +430,7 @@ udisks_mount_monitor_get_mountinfo (UDisksMountMonitor  *monitor,
         continue;
 
       if (sscanf (lines[n],
-                  "%d %d %d:%d %s %s",
+                  "%d %d %d:%d " PATH_MAX_FMT " " PATH_MAX_FMT,
                   &mount_id,
                   &parent_id,
                   &major,
@@ -436,6 +441,8 @@ udisks_mount_monitor_get_mountinfo (UDisksMountMonitor  *monitor,
           udisks_warning ("Error parsing line '%s'", lines[n]);
           continue;
         }
+      encoded_root[sizeof encoded_root - 1] = '\0';
+      encoded_mount_point[sizeof encoded_mount_point - 1] = '\0';
 
       /* Temporary work-around for btrfs, see
        *
@@ -450,15 +457,17 @@ udisks_mount_monitor_get_mountinfo (UDisksMountMonitor  *monitor,
           sep = strstr (lines[n], " - ");
           if (sep != NULL)
             {
-              gchar fstype[PATH_MAX];
-              gchar mount_source[PATH_MAX];
+              gchar fstype[PATH_MAX + 1];
+              gchar mount_source[PATH_MAX + 1];
               struct stat statbuf;
 
-              if (sscanf (sep + 3, "%s %s", fstype, mount_source) != 2)
+              if (sscanf (sep + 3, PATH_MAX_FMT " " PATH_MAX_FMT, fstype, mount_source) != 2)
                 {
                   udisks_warning ("Error parsing things past - for '%s'", lines[n]);
                   continue;
                 }
+              fstype[sizeof fstype - 1] = '\0';
+              mount_source[sizeof mount_source - 1] = '\0';
 
               if (g_strcmp0 (fstype, "btrfs") != 0)
                 continue;
@@ -546,7 +555,7 @@ udisks_mount_monitor_get_swaps (UDisksMountMonitor  *monitor,
   lines = g_strsplit (contents, "\n", 0);
   for (n = 0; lines[n] != NULL; n++)
     {
-      gchar filename[PATH_MAX];
+      gchar filename[PATH_MAX + 1];
       struct stat statbuf;
       dev_t dev;
 
@@ -557,11 +566,12 @@ udisks_mount_monitor_get_swaps (UDisksMountMonitor  *monitor,
       if (strlen (lines[n]) == 0)
         continue;
 
-      if (sscanf (lines[n], "%s", filename) != 1)
+      if (sscanf (lines[n], PATH_MAX_FMT, filename) != 1)
         {
           udisks_warning ("Error parsing line '%s'", lines[n]);
           continue;
         }
+      filename[sizeof filename - 1] = '\0';
 
       if (stat (filename, &statbuf) != 0)
         {