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authorTodd Kjos <tkjos@android.com>2018-12-14 15:58:21 -0800
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2018-12-19 09:40:13 +0100
commit80cd795630d6526ba729a089a435bf74a57af927 (patch)
treebc1d2b779bf5e506c66f96ee2210101c17652b59 /fs/file.c
parent2701e804f00f79823f69f37c87fef171ac345484 (diff)
binder: fix use-after-free due to ksys_close() during fdget()
44d8047f1d8 ("binder: use standard functions to allocate fds") exposed a pre-existing issue in the binder driver. fdget() is used in ksys_ioctl() as a performance optimization. One of the rules associated with fdget() is that ksys_close() must not be called between the fdget() and the fdput(). There is a case where this requirement is not met in the binder driver which results in the reference count dropping to 0 when the device is still in use. This can result in use-after-free or other issues. If userpace has passed a file-descriptor for the binder driver using a BINDER_TYPE_FDA object, then kys_close() is called on it when handling a binder_ioctl(BC_FREE_BUFFER) command. This violates the assumptions for using fdget(). The problem is fixed by deferring the close using task_work_add(). A new variant of __close_fd() was created that returns a struct file with a reference. The fput() is deferred instead of using ksys_close(). Fixes: 44d8047f1d87a ("binder: use standard functions to allocate fds") Suggested-by: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Todd Kjos <tkjos@google.com> Cc: stable <stable@vger.kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'fs/file.c')
-rw-r--r--fs/file.c29
1 files changed, 29 insertions, 0 deletions
diff --git a/fs/file.c b/fs/file.c
index 7ffd6e9d103d..8d059d8973e9 100644
--- a/fs/file.c
+++ b/fs/file.c
@@ -640,6 +640,35 @@ out_unlock:
}
EXPORT_SYMBOL(__close_fd); /* for ksys_close() */
+/*
+ * variant of __close_fd that gets a ref on the file for later fput
+ */
+int __close_fd_get_file(unsigned int fd, struct file **res)
+{
+ struct files_struct *files = current->files;
+ struct file *file;
+ struct fdtable *fdt;
+
+ spin_lock(&files->file_lock);
+ fdt = files_fdtable(files);
+ if (fd >= fdt->max_fds)
+ goto out_unlock;
+ file = fdt->fd[fd];
+ if (!file)
+ goto out_unlock;
+ rcu_assign_pointer(fdt->fd[fd], NULL);
+ __put_unused_fd(files, fd);
+ spin_unlock(&files->file_lock);
+ get_file(file);
+ *res = file;
+ return filp_close(file, files);
+
+out_unlock:
+ spin_unlock(&files->file_lock);
+ *res = NULL;
+ return -ENOENT;
+}
+
void do_close_on_exec(struct files_struct *files)
{
unsigned i;