ext4: check to make sure the rename(2)'s destination is not freed

If the destination of the rename(2) system call exists, the inode's
link count (i_nlinks) must be non-zero.  If it is, the inode can end
up on the orphan list prematurely, leading to all sorts of hilarity,
including a use-after-free.

https://bugzilla.kernel.org/show_bug.cgi?id=200931

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reported-by: Wen Xu <wen.xu@gatech.edu>
Cc: stable@vger.kernel.org

diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
index 116ff68..377d516 100644 (file)
--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -3478,6 +3478,12 @@ static int ext4_rename(struct inode *old_dir, struct dentry *old_dentry,
        int credits;
        u8 old_file_type;
 
+       if (new.inode && new.inode->i_nlink == 0) {
+               EXT4_ERROR_INODE(new.inode,
+                                "target of rename is already freed");
+               return -EFSCORRUPTED;
+       }
+
        if ((ext4_test_inode_flag(new_dir, EXT4_INODE_PROJINHERIT)) &&
            (!projid_eq(EXT4_I(new_dir)->i_projid,
                        EXT4_I(old_dentry->d_inode)->i_projid)))