Add xfuse_path_in_xfuse_fs()

2 files changed, 137 insertions, 2 deletions

diff --git a/sesman/chansrv/chansrv_fuse.c b/sesman/chansrv/chansrv_fuse.c
index 1b3a0f9e..a2ea8d23 100644
--- a/sesman/chansrv/chansrv_fuse.c
+++ b/sesman/chansrv/chansrv_fuse.c
@@ -18,6 +18,11 @@
 
 /* FUSE mount point */
 char g_fuse_root_path[256] = "";
+#ifdef XRDP_FUSE
+static const char *g_fuse_root_path_basename; /* See xfuse_path_in_xfuse_fs() */
+static int g_fuse_root_parent_dev;   /* Ditto */
+static int g_fuse_root_parent_ino;   /* Ditto */
+#endif
 char g_fuse_clipboard_path[256] = ""; /* for clipboard use */
 
 #if defined(HAVE_CONFIG_H)
@@ -122,6 +127,11 @@ void xfuse_devredir_cb_rename_file(struct state_rename *fip,
 void xfuse_devredir_cb_file_close(struct state_close *fip)
 {}
 
+int xfuse_path_in_xfuse_fs(const char *path)
+{
+    return 0;
+}
+
 #else
 
 /******************************************************************************
@@ -324,6 +334,7 @@ static char *g_buffer = 0;
 static int g_fd = 0;
 static tintptr g_bufsize = 0;
 
+
 /* forward declarations for internal access */
 static int xfuse_init_xrdp_fs(void);
 static int xfuse_deinit_xrdp_fs(void);
@@ -461,6 +472,7 @@ int
 xfuse_init(void)
 {
     struct fuse_args args = FUSE_ARGS_INIT(0, NULL);
+    char *p;
 
     /* if already inited, just return */
     if (g_xfuse_inited)
@@ -507,16 +519,59 @@ xfuse_init(void)
         g_snprintf(g_fuse_root_path, sizeof(g_fuse_root_path), "%s/%s",
                    g_getenv("HOME"), g_cfg->fuse_mount_name);
     }
+
+    /* Remove all trailing '/' from the root path */
+    p = g_fuse_root_path + g_strlen(g_fuse_root_path);
+    while ( p > g_fuse_root_path && *(p - 1) == '/')
+    {
+        --p;
+        *p = '\0';
+    }
+
+    /* This shouldn't happen */
+    if (g_strlen(g_fuse_root_path) == 0)
+    {
+        LOG(LOG_LEVEL_ERROR,
+            "Fuse root path is empty after removing trailing '/'");
+        return -1;
+    }
+
     g_snprintf(g_fuse_clipboard_path, 255, "%s/.clipboard", g_fuse_root_path);
 
+    /* Get the characteristics of the parent directory of the FUSE mount
+     * point. Used by xfuse_path_in_xfuse_fs() */
+    p = (char *)g_strrchr(g_fuse_root_path, '/');
+    if (p != NULL)
+    {
+        /* Temporarily finish the root path at this point */
+        *p = '\0';
+        g_fuse_root_path_basename = p + 1;
+        g_fuse_root_parent_dev = g_file_get_device_number(g_fuse_root_path);
+        g_fuse_root_parent_ino = g_file_get_inode_num(g_fuse_root_path);
+        *p = '/';
+    }
+    else
+    {
+        g_fuse_root_parent_dev = -1;
+        g_fuse_root_parent_ino = -1;
+    }
+
+    if (g_fuse_root_parent_dev == -1 || g_fuse_root_parent_ino == -1)
+    {
+        LOG(LOG_LEVEL_ERROR,
+            "Unable to obtain characteristics of directory containing %s",
+            g_fuse_root_path);
+        return -1;
+    }
+
     /* if FUSE mount point does not exist, create it */
     if (!g_directory_exist(g_fuse_root_path))
     {
         (void)g_create_path(g_fuse_root_path);
         if (!g_create_dir(g_fuse_root_path))
         {
-            LOG_DEVEL(LOG_LEVEL_ERROR, "mkdir %s failed. If %s is already mounted, you must "
-                      "first unmount it", g_fuse_root_path, g_fuse_root_path);
+            LOG(LOG_LEVEL_ERROR, "mkdir %s failed. If %s is already mounted, you must "
+                "first unmount it", g_fuse_root_path, g_fuse_root_path);
             return -1;
         }
     }
@@ -1491,6 +1546,77 @@ void xfuse_devredir_cb_file_close(struct state_close *fip)
     free(fip);
 }
 
+/*
+ * Determine is a file is in the FUSE filesystem
+ *
+ * The whole purpose of this function is to avoid deadlocks. If we try
+ * to determine the size (or any other attribute) of a file in the FUSE
+ * filesystem, the kernel will block the calling thread and send a message
+ * to libfuse. Since we're single-threaded, this will result in deadlock.
+ *
+ * Ideally we'd use a stat() of the file to compare with a stat() of
+ * the mountpoint. This won't work however, for the reasons outline above.
+ *
+ * A simple implementation might be to compare the start of the filename
+ * with the FUSE mount point. This will work, but can easily be defeated,
+ * (perhaps unintentionally) by symlinks in the path.
+ *
+ * The approach taken here is to record the basename of the FUSE mount
+ * point directory (e.g. 'thinclient_drives') and look for that in the
+ * passed-in filename as a directory element. If we find it, we look
+ * at the device name and inode number of the parent directory of the
+ * FUSE mount point. If these match we consider the filename to be in
+ * the FUSE filesystem.
+ */
+int xfuse_path_in_xfuse_fs(const char *path)
+{
+    char *wpath = NULL; /* Writeable copy of path */
+    char *p;
+    int blen = g_strlen(g_fuse_root_path_basename);
+    int rv = 0;
+
+    if ((wpath = g_strdup(path)) == NULL)
+    {
+        LOG(LOG_LEVEL_ERROR, "system out of memory");
+    }
+    else
+    {
+        /* Look ahead in the string for the basename of the FUSE mount point */
+        for (p = wpath;
+                (p = g_strstr(p, g_fuse_root_path_basename)) != NULL ;
+                p = p + 1)
+        {
+            /* Is this string preceded by a '/' ? */
+            if (p == wpath || *(p - 1) != '/')
+            {
+                continue;
+            }
+
+            /* Is the string followed by a '/' or '\0' ? We know it's
+             * valid to look ahead this far in the string, as g_strstr()
+             * tells us it is */
+            if (*(p + blen) != '/' && *(p + blen) != '\0')
+            {
+                continue;
+            }
+
+            /* Temporarily terminate the string early, and check the
+             * file system characteristics of the preceding directory */
+            *(p - 1) = '\0';
+
+            if (g_file_get_device_number(wpath) == g_fuse_root_parent_dev &&
+                    g_file_get_inode_num(wpath) == g_fuse_root_parent_ino)
+            {
+                rv = 1;
+                break;
+            }
+            *(p - 1) = '/';
+        }
+        g_free(wpath);
+    }
+    return rv;
+}
+
 /******************************************************************************
 **                                                                           **
 **                           callbacks for fuse                              **
diff --git a/sesman/chansrv/chansrv_fuse.h b/sesman/chansrv/chansrv_fuse.h
index 5a125d11..a456bc90 100644
--- a/sesman/chansrv/chansrv_fuse.h
+++ b/sesman/chansrv/chansrv_fuse.h
@@ -114,4 +114,13 @@ void xfuse_devredir_cb_rename_file(struct state_rename *fip,
 
 void xfuse_devredir_cb_file_close(struct state_close *fip);
 
+/*
+ * Returns true if a filesystem path lies in the FUSE filesystem
+ *
+ * Use to prevent deadlocks. For example, if chansrv tries to open
+ * a file in the FUSE filesystem it will fail, as it will call back
+ * into itself to handle the I/O
+ */
+int xfuse_path_in_xfuse_fs(const char *path);
+
 #endif