[PATCH] To add NULL pointer check

[P J P <ppandit@redhat.com>]

    Hello,

Commit - fa9150a84c - replaces a call to generic_writepages() in 
f2fs_write_data_pages() with write_cache_pages(), with a function pointer 
argument pointing to routine: __f2fs_writepage.

  -> https://git.kernel.org/linus/fa9150a84ca333f68127097c4fa1eda4b3913a22

The patch below adds a NULL pointer check, from generic_writepages(), to avoid 
a possible NULL pointer dereference, in case if - mapping->a_ops->writepage - 
is NULL.

===
$ git diff
diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index 7bd22a2..9841372 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -550,9 +550,16 @@ redirty_out:
  static int __f2fs_writepage(struct page *page, struct writeback_control *wbc,
                         void *data)
  {
+       int ret = 0;
         struct address_space *mapping = data;
-       int ret = mapping->a_ops->writepage(page, wbc);
+
+       /* deal with chardevs and other special file */
+       if (!mapping->a_ops->writepage)
+               return ret;
+
+       ret = mapping->a_ops->writepage(page, wbc);
         mapping_set_error(mapping, ret);
+
         return ret;
  }
===


Thank you.
--
Prasad J Pandit / Red Hat Security Response Team
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