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ovl: fix missing negative dentry check in ovl_rename()

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commit a295aef603e109a47af355477326bd41151765b6 upstream.

The following reproducer

  mkdir lower upper work merge
  touch lower/old
  touch lower/new
  mount -t overlay overlay -olowerdir=lower,upperdir=upper,workdir=work merge
  rm merge/new
  mv merge/old merge/new & unlink upper/new

may result in this race:

PROCESS A:
  rename("merge/old", "merge/new");
  overwrite=true,ovl_lower_positive(old)=true,
  ovl_dentry_is_whiteout(new)=true -> flags |= RENAME_EXCHANGE

PROCESS B:
  unlink("upper/new");

PROCESS A:
  lookup newdentry in new_upperdir
  call vfs_rename() with negative newdentry and RENAME_EXCHANGE

Fix by adding the missing check for negative newdentry.

Signed-off-by: Zheng Liang <zhengliang6@huawei.com>
Fixes: e9be9d5e76e3 ("overlay filesystem")
Cc: <stable@vger.kernel.org> # v3.18
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Zheng Liang 2021-09-24 09:16:27 +08:00 committed by Greg Kroah-Hartman
parent 29e0a6c4d9
commit 286f94453f
1 changed files with 7 additions and 3 deletions

10
fs/overlayfs/dir.c

@ -926,9 +926,13 @@ static int ovl_rename2(struct inode *olddir, struct dentry *old,
goto out_dput;
}
} else {
if (!d_is_negative(newdentry) &&
(!new_opaque || !ovl_is_whiteout(newdentry)))
goto out_dput;
if (!d_is_negative(newdentry)) {
if (!new_opaque || !ovl_is_whiteout(newdentry))
goto out_dput;
} else {
if (flags & RENAME_EXCHANGE)
goto out_dput;
}
}
if (olddentry == trap)