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SubjectRe: [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@atomicpeace.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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