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ovl: fix missing negative dentry check in ovl_rename()

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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: e9be9d5e76 ("overlay filesystem")
Cc: <stable@vger.kernel.org> # v3.18
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
This commit is contained in:
Zheng Liang 2021-09-24 09:16:27 +08:00 committed by Miklos Szeredi
parent 6880fa6c56
commit a295aef603
1 changed files with 7 additions and 3 deletions
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10
fs/overlayfs/dir.c
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@ -1219,9 +1219,13 @@ static int ovl_rename(struct user_namespace *mnt_userns, struct inode *olddir,
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)