Re: [PATCH] ecryptfs: Restore support for both encrypted and unencrypted file names

[Tyler Hicks]

Hello Guenter

On 02/13/2018 04:36 PM, Guenter Roeck wrote:
> Commit 88ae4ab9802e ("ecryptfs_lookup(): try either only encrypted or
> plaintext name") was supposed to fix a situation where two files with
> the same name and same inode could be created in ecryptfs. One of those
> files had an encrypted file name, the other file name was unencrypted.

That's correct. Al was concerned about possible deadlocks with aliased
dentries and I thought it would be best to only support encrypted and
unencrypted but not both.

> 
> After commit 88ae4ab9802e, having a mix of encrypted and unencrypted file
> names is no longer supposed to be possible. However, that is not the case.
> The only difference is that it is now even easier to create a situation
> where two files with the same name coexist (one encrypted and the other
> not encrypted). In practice, this looks like the following (files
> created with v4.14.12).
> 
> ecryptfs mounted with file name encryption enabled:
> 
> $ ls -li
> total 48
> 5252822 -rw-rw-r-- 1 groeck groeck 10 Jan 20 13:02 myfile
> 5252822 -rw-rw-r-- 1 groeck groeck 10 Jan 20 13:02 myfile
> 5252824 -rw-rw-r-- 1 groeck groeck 10 Jan 20 15:36 myfile2
> 5252824 -rw-rw-r-- 1 groeck groeck 10 Jan 20 15:36 myfile2
> $ grep . *
> myfile:encrypted
> myfile:encrypted
> myfile2:encrypted
> myfile2:encrypted
> 
> $ ls -li
> total 48
> 5252824 -rw-rw-r-- 1 groeck groeck 10 Jan 20 15:36
> ECRYPTFS_FNEK_ENCRYPTED.FWbF9U6H6L6ekEZYGWnkfR4wMiyeTVoCeVun.BU8Zu5-njbcIPoApxk7-E--
> 5252822 -rw-rw-r-- 1 groeck groeck 10 Jan 20 13:02
> ECRYPTFS_FNEK_ENCRYPTED.FWbF9U6H6L6ekEZYGWnkfR4wMiyeTVoCeVunt0fda7t9YCtJ70cm911yZ---
> 5252817 -rw-rw-r-- 1 groeck groeck 12 Jan 20 12:52 myfile
> 5252827 -rw-rw-r-- 1 groeck groeck 12 Jan 20 15:37 myfile2
> 
> $ grep . *
> ECRYPTFS_FNEK_ENCRYPTED.FWbF9U6H6L6ekEZYGWnkfR4wMiyeTVoCeVun.BU8Zu5-njbcIPoApxk7-E--:encrypted
> ECRYPTFS_FNEK_ENCRYPTED.FWbF9U6H6L6ekEZYGWnkfR4wMiyeTVoCeVunt0fda7t9YCtJ70cm911yZ---:encrypted
> myfile:unencrypted
> myfile2:unencrypted
> 
> Creating a file with file name encryption disabled and remounting with
> file name encryption enabled results in the following.
> 
> $ ls -li
> ls: cannot access 'myfile3': No such file or directory
> total 48
> 5252822 -rw-rw-r-- 1 groeck groeck 10 Jan 20 13:02 myfile
> 5252822 -rw-rw-r-- 1 groeck groeck 10 Jan 20 13:02 myfile
> 5252824 -rw-rw-r-- 1 groeck groeck 10 Jan 20 15:36 myfile2
> 5252824 -rw-rw-r-- 1 groeck groeck 10 Jan 20 15:36 myfile2
>       ? -????????? ? ?      ?       ?            ? myfile3
> 
> Prior to commit 88ae4ab9802e, the file system had to be mounted with
> encrypted file names first to create a file, then the same had to be
> repeated after mounting with unencrypted file names. Now the duplicate
> files can be created both ways (unencrypted _or_ encrypted first).
> 
> The only real difference is that it is no longer possible to have a
> _working_ combination of encrypted and unencrypted file names. In other
> words, commit 88ae4ab9802e results in reduced functionality with no
> benefit whatsoever.
> 
> Restore ability to have a mix of unencrypted and encrypted files.
> This effectively reverts commit 88ae4ab9802e, but the code is now
> better readable since it avoids a number of goto statements.

I'd like for us to correctly fix 88ae4ab9802e rather than try to support
both filename types under a single mount since that's complex and there
are unknown corner cases to consider. I think this can be done by not
copying up the lower filename when an error is encountered in
ecryptfs_decode_and_decrypt_filename(). If filename encryption is
enabled, it should only return decrypted filenames or an error if it
isn't possible to decrypt the lower filename.

Tyler

> 
> Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
> Signed-off-by: Guenter Roeck <linux@xxxxxxxxxxxx>
> ---
>  fs/ecryptfs/inode.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/ecryptfs/inode.c b/fs/ecryptfs/inode.c
> index 847904aa63a9..14a5c096ead6 100644
> --- a/fs/ecryptfs/inode.c
> +++ b/fs/ecryptfs/inode.c
> @@ -392,11 +392,11 @@ static struct dentry *ecryptfs_lookup(struct inode *ecryptfs_dir_inode,
>  	int rc = 0;
>  
>  	lower_dir_dentry = ecryptfs_dentry_to_lower(ecryptfs_dentry->d_parent);
> -
> +	lower_dentry = lookup_one_len_unlocked(name, lower_dir_dentry, len);
>  	mount_crypt_stat = &ecryptfs_superblock_to_private(
>  				ecryptfs_dentry->d_sb)->mount_crypt_stat;
> -	if (mount_crypt_stat
> -	    && (mount_crypt_stat->flags & ECRYPTFS_GLOBAL_ENCRYPT_FILENAMES)) {
> +	if (IS_ERR(lower_dentry) &&
> +	    (mount_crypt_stat->flags & ECRYPTFS_GLOBAL_ENCRYPT_FILENAMES)) {
>  		rc = ecryptfs_encrypt_and_encode_filename(
>  			&encrypted_and_encoded_name, &len,
>  			mount_crypt_stat, name, len);
> @@ -405,10 +405,10 @@ static struct dentry *ecryptfs_lookup(struct inode *ecryptfs_dir_inode,
>  			       "filename; rc = [%d]\n", __func__, rc);
>  			return ERR_PTR(rc);
>  		}
> -		name = encrypted_and_encoded_name;
> +		lower_dentry = lookup_one_len_unlocked(
> +			encrypted_and_encoded_name, lower_dir_dentry, len);
>  	}
>  
> -	lower_dentry = lookup_one_len_unlocked(name, lower_dir_dentry, len);
>  	if (IS_ERR(lower_dentry)) {
>  		ecryptfs_printk(KERN_DEBUG, "%s: lookup_one_len() returned "
>  				"[%ld] on lower_dentry = [%s]\n", __func__,
>

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