check-rename-destination-is-not-freed

   1 ext4: check to make sure the rename(2)'s destination is not freed
   2
   3 If the destination of the rename(2) system call exists, the inode's
   4 link count (i_nlinks) must be non-zero.  If it is, the inode can end
   5 up on the orphan list prematurely, leading to all sorts of hilarity,
   6 including a use-after-free.
   7
   8 https://bugzilla.kernel.org/show_bug.cgi?id=200931
   9
  10 Signed-off-by: Theodore Ts'o <tytso@mit.edu>
  11 Reported-by: Wen Xu <wen.xu@gatech.edu>
  12 Cc: stable@vger.kernel.org
  13 ---
  14  fs/ext4/namei.c | 6 ++++++
  15  1 file changed, 6 insertions(+)
  16
  17 diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
  18 index 116ff68c5bd4..377d516c475f 100644
  19 --- a/fs/ext4/namei.c
  20 +++ b/fs/ext4/namei.c
  21 @@ -3478,6 +3478,12 @@ static int ext4_rename(struct inode *old_dir, struct dentry *old_dentry,
  22         int credits;
  23         u8 old_file_type;
  24
  25 +       if (new.inode && new.inode->i_nlink == 0) {
  26 +               EXT4_ERROR_INODE(new.inode,
  27 +                                "target of rename is already freed");
  28 +               return -EFSCORRUPTED;
  29 +       }
  30 +
  31         if ((ext4_test_inode_flag(new_dir, EXT4_INODE_PROJINHERIT)) &&
  32             (!projid_eq(EXT4_I(new_dir)->i_projid,
  33                         EXT4_I(old_dentry->d_inode)->i_projid)))