linux-kernel - Re: [f2fs-dev] [PATCH] f2fs: don't allow rename unencrypted file to encrypted directory

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Date:   Wed, 8 Mar 2017 21:35:25 +0800
From:   Kinglong Mee <kinglongmee@...il.com>
To:     Chao Yu <yuchao0@...wei.com>, jaegeuk@...nel.org
Cc:     chao@...nel.org, linux-kernel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net,
        Kinglong Mee <kinglongmee@...il.com>
Subject: Re: [f2fs-dev] [PATCH] f2fs: don't allow rename unencrypted file to
 encrypted directory

On 3/8/2017 20:08, Chao Yu wrote:
> In commit d9cdc9033181 ("ext4 crypto: enforce context consistency") we
> declared that:
> 
> 2) All files or directories in a directory must be protected using the
>     same key as their containing directory.
> 
> But in f2fs_cross_rename there is a vulnerability that allow to cross
> rename unencrypted file into encrypted directory, it needs to be refused.

fscrypt_has_permitted_context has do the checking as this patch,

168         /* no restrictions if the parent directory is not encrypted */
169         if (!parent->i_sb->s_cop->is_encrypted(parent))
170                 return 1;
171         /* if the child directory is not encrypted, this is always a problem */
172         if (!parent->i_sb->s_cop->is_encrypted(child))
173                 return 0;

So, the cross rename unencrypted file into encrypted directory is permitted right now. 

I have a encrypted directory "ncry",  "new" is unencrypted file.

[root@...testnic f2fs]# renameat2 -x encry/hello new
Operation not permitted
[root@...testnic f2fs]# renameat2 -x encry/hello new
Operation not permitted

How do you test it? 

thanks,
Kinglong Mee
> 
> Signed-off-by: Chao Yu <yuchao0@...wei.com>
> ---
>  fs/f2fs/namei.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/fs/f2fs/namei.c b/fs/f2fs/namei.c
> index 25c073f6c7d4..8de684b84cb9 100644
> --- a/fs/f2fs/namei.c
> +++ b/fs/f2fs/namei.c
> @@ -855,6 +855,10 @@ static int f2fs_cross_rename(struct inode *old_dir, struct dentry *old_dentry,
>  			!fscrypt_has_encryption_key(new_dir)))
>  		return -ENOKEY;
>  
> +	if (f2fs_encrypted_inode(old_dir) && !f2fs_encrypted_inode(new_inode) ||
> +		f2fs_encrypted_inode(new_dir) && !f2fs_encrypted_inode(old_inode))
> +		return -EPERM;
> +
>  	if ((f2fs_encrypted_inode(old_dir) || f2fs_encrypted_inode(new_dir)) &&
>  			(old_dir != new_dir) &&
>  			(!fscrypt_has_permitted_context(new_dir, old_inode) ||
>