Changeset 40feeac in mainline

Timestamp:

2017-12-03T22:14:40Z (7 years ago)

Author:

Jiří Zárevúcky <zarevucky.jiri@…>

Branches:

lfn, master, serial, ticket/834-toolchain-update, topic/msim-upgrade, topic/simplify-dev-export

Children:

8e3498b

Parents:

38d150e

Message:

Avoid race condition in vfs_clone().

The file descriptor could have been reallocated between the freeing
and the assigning, which would make it fail spuriously. Avoid
the error by moving deallocation inside the critical section.

Location:

uspace/srv/vfs

Files:

• vfs_file.c (modified) (3 diffs)
• vfs_ops.c (modified) (1 diff)

uspace/srv/vfs/vfs_file.c

@@ -257 +257 @@
 }
 
+static int _vfs_fd_free_locked(vfs_client_data_t *vfs_data, int fd)
+{
+        if ((fd < 0) || (fd >= MAX_OPEN_FILES) || !vfs_data->files[fd]) {
+                return EBADF;
+        }
+
+        int rc = vfs_file_delref(vfs_data, vfs_data->files[fd]);
+        vfs_data->files[fd] = NULL;
+        return rc;
+}
+
 static int _vfs_fd_free(vfs_client_data_t *vfs_data, int fd)
 {
@@ -265 +276 @@
 
         fibril_mutex_lock(&vfs_data->lock);     
-        if ((fd < 0) || (fd >= MAX_OPEN_FILES) || !vfs_data->files[fd]) {
-                fibril_mutex_unlock(&vfs_data->lock);
-                return EBADF;
-        }
-        
-        rc = vfs_file_delref(vfs_data, vfs_data->files[fd]);
-        vfs_data->files[fd] = NULL;
+        rc = _vfs_fd_free_locked(vfs_data, fd);
         fibril_mutex_unlock(&vfs_data->lock);
         
@@ -308 +313 @@
                 return EBADF;
         }
-        if (FILES[fd] != NULL) {
-                fibril_mutex_unlock(&VFS_DATA->lock);
-                return EEXIST;
-        }
+
+        /* Make sure fd is closed. */
+        (void) _vfs_fd_free_locked(VFS_DATA, fd);
+        assert(FILES[fd] == NULL);
         
         FILES[fd] = file;

uspace/srv/vfs/vfs_ops.c

@@ -102 +102 @@
 
         if (newfd != -1) {
-                /* Make sure newfd is closed. */
-                (void) vfs_fd_free(newfd);
                 /* Assign the old file to newfd. */
                 rc = vfs_fd_assign(oldfile, newfd);