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[Joseph Salisbury <joseph.salisbury@xxxxxxxxxxxxx>]

This issue appears to be an upstream bug, since the code is the same in
the current v4.1-rc3 mainline kernel.

Would it be possible for you to open an upstream bug report[0]? That
will allow the upstream Developers to examine the issue, and may provide
a quicker resolution to the bug.

Please follow the instructions on the wiki page[0]. The first step is to
email the appropriate mailing list. If no response is received, then a
bug may be opened on bugzilla.kernel.org.

Once this bug is reported upstream, please add the tag: 'kernel-bug-
reported-upstream'.

[0] https://wiki.ubuntu.com/Bugs/Upstream/kernel

** Tags added: kernel-bug-exists-upstream kernel-da-key

** Changed in: linux (Ubuntu)
       Status: Incomplete => Triaged

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https://bugs.launchpad.net/bugs/1455364

Title:
  the wrong return value of function ubifs_fill_super()

Status in linux package in Ubuntu:
  Triaged

Bug description:
  In function ubifs_fill_super() at fs/ubifs/super.c: 1955, the call to d_alloc_root() in line 2058 may return a NULL pointer, and thus function ubifs_fill_super() will return the value of variable err. And, the function ubifs_fill_super() will return 0 at last when it runs well. However, when the call to d_alloc_root() in line 2058 return a NULL pointer, the value of err is 0. So the function ubifs_fill_super() will return 0 to its caller functions when it runs error because of the failing call to d_alloc_root(), leading to a wrong return value of function ubifs_fill_super().
  The related code snippets in ubifs_fill_super() is as following.
  ubifs_fill_super @@fs/ubifs/super.c: 1955
  1955 static int ubifs_fill_super(struct super_block *sb, void *data, int silent)
  1956 {
               ...
  2045         err = mount_ubifs(c);
  2046         if (err) {
  2047                 ubifs_assert(err < 0);
  2048                 goto out_unlock;
  2049         }
  2050 
  2051         /* Read the root inode */
  2052         root = ubifs_iget(sb, UBIFS_ROOT_INO);
  2053         if (IS_ERR(root)) {
  2054                 err = PTR_ERR(root);
  2055                 goto out_umount;
  2056         }
  2057 
  2058         sb->s_root = d_alloc_root(root);
  2059         if (!sb->s_root)
  2060                 goto out_iput;
  2061 
  2062         mutex_unlock(&c->umount_mutex);
  2063         return 0;
  2064 
  2065 out_iput:
  2066         iput(root);
  2067 out_umount:
  2068         ubifs_umount(c);
  2069 out_unlock:
  2070         mutex_unlock(&c->umount_mutex);
  2071 out_bdi:
  2072         bdi_destroy(&c->bdi);
  2073 out_close:
  2074         ubi_close_volume(c->ubi);
  2075 out_free:
  2076         kfree(c);
  2077         return err;
  2078 }

  Generally, the return value of caller functions which call function d_alloc_root() shall be set to a negative error code when the call to d_alloc_root() returns a NULL pointer, like the following codes in another file.
  bfs_fill_super @@fs/bfs/inode.c: 317
  317 static int bfs_fill_super(struct super_block *s, void *data, int silent)
  318 {
               ...
  371         s->s_root = d_alloc_root(inode);
  372         if (!s->s_root) {
  373                 iput(inode);
  374                 ret = -ENOMEM;
  375                 goto out2;
  376         }
               ...
  444         return 0;
  445 
  446 out3:
  447         dput(s->s_root);
  448         s->s_root = NULL;
  449 out2:
  450         kfree(info->si_imap);
  451 out1:
  452         brelse(sbh);
  453 out:
  454         mutex_destroy(&info->bfs_lock);
  455         kfree(info);
  456         s->s_fs_info = NULL;
  457         return ret;
  458 }

  Thank you

  RUC_Soft_Sec

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