linux-ext4 - Re: [PATCH] fscrypto: fix to null-terminate encrypted filename in fname

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Date:   Sun, 28 Aug 2016 01:13:30 -0400
From:   Theodore Ts'o <tytso@....edu>
To:     Chao Yu <chao@...nel.org>
Cc:     jaegeuk@...nel.org, linux-f2fs-devel@...ts.sourceforge.net,
        linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org,
        Chao Yu <yuchao0@...wei.com>
Subject: Re: [PATCH] fscrypto: fix to null-terminate encrypted filename in
 fname_encrypt

On Sun, Aug 28, 2016 at 09:13:28AM +0800, Chao Yu wrote:
> From: Chao Yu <yuchao0@...wei.com>
> 
> This patch fixes to add null character at the end of encrypted filename
> in fname_encrypt, in order to avoid incorrectly traversing random data
> located after target filename. The call stack is as below:
> 
> - f2fs_add_link
>  - __f2fs_add_link
>   - fscrypt_setup_filename
>    - fscrypt_fname_alloc_buffer		allocate buffer for @fname
>    - fname_encrypt			didn't set null character for @fname
>   - f2fs_add_regular_entry		init qstr with @fname
>    - init_inode_metadata
>     - f2fs_init_security
>      - security_inode_init_security
>       - selinux_inode_init_security
>        - selinux_determine_inode_label
>         - security_transition_sid
> 	 - security_compute_sid
> 	  - filename_compute_type
> 	   - hashtab_search
> 	    - filenametr_hash		traverse @fname as one which has null character

The problem is not in fname_encrypt(), but rather that
security_inode_init_security() should be given the _unencrypted_
filename.

In ext4 security_inode_init_security() is called with the qstr from
the dentry, not the encrypted qstr --- in fact we call
security_inode_init_security before we call fname_encrypt.

SELinux needs the unencrypted filename in order to decide which
SELinux rules / labels should apply.

					- Ted
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