linux-kernel - Re: [PATCH 1/1] eCryptfs: check for eCryptfs cipher support at mount

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Message-ID: <20120711171152.GA16475@boyd>
Date:	Wed, 11 Jul 2012 10:11:53 -0700
From:	Tyler Hicks <tyhicks@...onical.com>
To:	Tim Sally <tsally@...micpeace.com>
Cc:	dustin.kirkland@...zang.com, ecryptfs@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] eCryptfs: check for eCryptfs cipher support at mount

On 2012-07-10 21:05:51, Tim Sally wrote:
> The issue occurs when eCryptfs is mounted with a cipher supported by
> the crypto subsystem but not by eCryptfs. The mount succeeds and an
> error does not occur until a write. This change checks for eCryptfs
> cipher support at mount time.
> 
> Resolves Launchpad issue #338914, reported by Tyler Hicks in 03/2009.
> https://bugs.launchpad.net/ecryptfs/+bug/338914

Hey Tim - Thanks for digging this one out of the bug tracker. :)

> 
> Signed-off-by: Tim Sally <tsally@...micpeace.com>
> ---
>  fs/ecryptfs/main.c |   24 ++++++++++++++++++++++++
>  1 file changed, 24 insertions(+)
> 
> diff --git a/fs/ecryptfs/main.c b/fs/ecryptfs/main.c
> index df217dc..4eb1fc6 100644
> --- a/fs/ecryptfs/main.c
> +++ b/fs/ecryptfs/main.c
> @@ -279,6 +279,8 @@ static int ecryptfs_parse_options(struct ecryptfs_sb_info *sbi, char *options,
>  	char *fnek_src;
>  	char *cipher_key_bytes_src;
>  	char *fn_cipher_key_bytes_src;
> +	struct ecryptfs_key_tfm *key_tfm = NULL;
> +	u8 cipher_code;
>  
>  	*check_ruid = 0;
>  
> @@ -456,6 +458,28 @@ static int ecryptfs_parse_options(struct ecryptfs_sb_info *sbi, char *options,
>  			goto out;
>  		}
>  	}
> +
> +	if (!ecryptfs_tfm_exists(mount_crypt_stat->global_default_cipher_name,
> +					&key_tfm)) {
> +		ecryptfs_printk(KERN_ERR,
> +				"Cipher %s was not initalized correctly.\n",
> +				mount_crypt_stat->global_default_cipher_name);
> +		rc = -EINVAL;
> +		mutex_unlock(&key_tfm_list_mutex);
> +		goto out;
> +	}

We already know that the tfm exists because we already checked for its
existence and added it if it didn't exist. We shouldn't need to do it
again here.

> +
> +	cipher_code = ecryptfs_code_for_cipher_string(key_tfm->cipher_name,
> +						key_tfm->key_size);
> +	if (!cipher_code) {
> +		ecryptfs_printk(KERN_ERR,
> +				"eCryptfs doesn't support: %s blocksize %zu.\n",
> +				key_tfm->cipher_name, key_tfm->key_size);
> +		rc = -EINVAL;
> +		mutex_unlock(&key_tfm_list_mutex);
> +		goto out;
> +	}

How about just calling

ecryptfs_code_for_cipher_string(mount_crypt_stat->global_default_cipher_name,
			mount_crypt_stat->global_default_cipher_key_size);

even before we lock the key_tfm_list_mutex a little above here? If that
fails, we don't even need to check for the tfm's existence or do
anything else besides error out.

Tyler

> +
>  	mutex_unlock(&key_tfm_list_mutex);
>  	rc = ecryptfs_init_global_auth_toks(mount_crypt_stat);
>  	if (rc)
> -- 
> 1.7.10.4
> 
> --
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