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Date: Wed, 27 Feb 2013 17:11:54 -0800
From: Tyler Hicks <tyhicks@...onical.com>
To: Kees Cook <keescook@...omium.org>
Cc: linux-kernel@...r.kernel.org,
Dustin Kirkland <dustin.kirkland@...zang.com>,
ecryptfs@...r.kernel.org
Subject: Re: [PATCH] eCryptfs: allow userspace messaging to be disabled
On 2013-02-27 16:30:42, Kees Cook wrote:
> When the userspace messaging (for the less common case of userspace key
> wrap/unwrap via ecryptfsd) is not needed, allow eCryptfs to build with
> it removed. This saves on kernel code size and reduces potential attack
> surface by removing the /dev/ecryptfs node.
>
> Signed-off-by: Kees Cook <keescook@...omium.org>
> Cc: Tyler Hicks <tyhicks@...onical.com>
Thanks for the patch, Kees!
I took a glance over the code and noticed that ECRYPTFS_VERSIONING_MASK
needs some adjusting. Its value is what is used to populate the
/sys/fs/ecryptfs/version mask and ecryptfs-utils uses that to determine
what feature support is available in the kernel.
The ECRYPTFS_VERSIONING_PUBKEY and ECRYPTFS_VERSIONING_DEVMISC bits
should not be set if CONFIG_ECRYPTFS_FS_MESSAGING is not defined.
Also, I don't think it makes sense to expose ECRYPTFS_VERSIONING_MASK to
userspace through linux/ecryptfs.h. For starters, that's the purpose of
the sysfs entry but an #ifdef CONFIG_ECRYPTF_FS_MESSAGING isn't going to
make any sense there. So I suppose we'd want to move
ECRYPTFS_VERSIONING_MASK to fs/ecryptfs/ecryptfs_kernel.h at this time,
too.
Does that sound sane to you?
Tyler
> ---
> fs/ecryptfs/Kconfig | 8 ++++++++
> fs/ecryptfs/Makefile | 7 +++++--
> fs/ecryptfs/ecryptfs_kernel.h | 27 +++++++++++++++++++++++++--
> fs/ecryptfs/keystore.c | 4 ++--
> 4 files changed, 40 insertions(+), 6 deletions(-)
>
> diff --git a/fs/ecryptfs/Kconfig b/fs/ecryptfs/Kconfig
> index e15ef38..434aa31 100644
> --- a/fs/ecryptfs/Kconfig
> +++ b/fs/ecryptfs/Kconfig
> @@ -12,3 +12,11 @@ config ECRYPT_FS
>
> To compile this file system support as a module, choose M here: the
> module will be called ecryptfs.
> +
> +config ECRYPT_FS_MESSAGING
> + bool "Enable notifications for userspace key wrap/unwrap"
> + depends on ECRYPT_FS
> + help
> + Enables the /dev/ecryptfs entry for use by ecryptfsd. This allows
> + for userspace to wrap/unwrap file encryption keys by other
> + backends, like OpenSSL.
> diff --git a/fs/ecryptfs/Makefile b/fs/ecryptfs/Makefile
> index 2cc9ee4..49678a6 100644
> --- a/fs/ecryptfs/Makefile
> +++ b/fs/ecryptfs/Makefile
> @@ -1,7 +1,10 @@
> #
> -# Makefile for the Linux 2.6 eCryptfs
> +# Makefile for the Linux eCryptfs
> #
>
> obj-$(CONFIG_ECRYPT_FS) += ecryptfs.o
>
> -ecryptfs-objs := dentry.o file.o inode.o main.o super.o mmap.o read_write.o crypto.o keystore.o messaging.o miscdev.o kthread.o debug.o
> +ecryptfs-y := dentry.o file.o inode.o main.o super.o mmap.o read_write.o \
> + crypto.o keystore.o kthread.o debug.o
> +
> +ecryptfs-$(CONFIG_ECRYPT_FS_MESSAGING) += messaging.o miscdev.o
> diff --git a/fs/ecryptfs/ecryptfs_kernel.h b/fs/ecryptfs/ecryptfs_kernel.h
> index cfb4b9f..b33722c 100644
> --- a/fs/ecryptfs/ecryptfs_kernel.h
> +++ b/fs/ecryptfs/ecryptfs_kernel.h
> @@ -399,7 +399,9 @@ struct ecryptfs_daemon {
> struct hlist_node euid_chain;
> };
>
> +#ifdef CONFIG_ECRYPT_FS_MESSAGING
> extern struct mutex ecryptfs_daemon_hash_mux;
> +#endif
>
> static inline size_t
> ecryptfs_lower_header_size(struct ecryptfs_crypt_stat *crypt_stat)
> @@ -604,6 +606,7 @@ int
> ecryptfs_setxattr(struct dentry *dentry, const char *name, const void *value,
> size_t size, int flags);
> int ecryptfs_read_xattr_region(char *page_virt, struct inode *ecryptfs_inode);
> +#ifdef CONFIG_ECRYPT_FS_MESSAGING
> int ecryptfs_process_response(struct ecryptfs_daemon *daemon,
> struct ecryptfs_message *msg, u32 seq);
> int ecryptfs_send_message(char *data, int data_len,
> @@ -612,6 +615,24 @@ int ecryptfs_wait_for_response(struct ecryptfs_msg_ctx *msg_ctx,
> struct ecryptfs_message **emsg);
> int ecryptfs_init_messaging(void);
> void ecryptfs_release_messaging(void);
> +#else
> +static inline int ecryptfs_init_messaging(void)
> +{
> + return 0;
> +}
> +static inline void ecryptfs_release_messaging(void)
> +{ }
> +static inline int ecryptfs_send_message(char *data, int data_len,
> + struct ecryptfs_msg_ctx **msg_ctx)
> +{
> + return -ENOTCONN;
> +}
> +static inline int ecryptfs_wait_for_response(struct ecryptfs_msg_ctx *msg_ctx,
> + struct ecryptfs_message **emsg)
> +{
> + return -ENOMSG;
> +}
> +#endif
>
> void
> ecryptfs_write_header_metadata(char *virt,
> @@ -649,12 +670,11 @@ int ecryptfs_read_lower_page_segment(struct page *page_for_ecryptfs,
> size_t offset_in_page, size_t size,
> struct inode *ecryptfs_inode);
> struct page *ecryptfs_get_locked_page(struct inode *inode, loff_t index);
> -int ecryptfs_exorcise_daemon(struct ecryptfs_daemon *daemon);
> -int ecryptfs_find_daemon_by_euid(struct ecryptfs_daemon **daemon);
> int ecryptfs_parse_packet_length(unsigned char *data, size_t *size,
> size_t *length_size);
> int ecryptfs_write_packet_length(char *dest, size_t size,
> size_t *packet_size_length);
> +#ifdef CONFIG_ECRYPT_FS_MESSAGING
> int ecryptfs_init_ecryptfs_miscdev(void);
> void ecryptfs_destroy_ecryptfs_miscdev(void);
> int ecryptfs_send_miscdev(char *data, size_t data_size,
> @@ -663,6 +683,9 @@ int ecryptfs_send_miscdev(char *data, size_t data_size,
> void ecryptfs_msg_ctx_alloc_to_free(struct ecryptfs_msg_ctx *msg_ctx);
> int
> ecryptfs_spawn_daemon(struct ecryptfs_daemon **daemon, struct file *file);
> +int ecryptfs_exorcise_daemon(struct ecryptfs_daemon *daemon);
> +int ecryptfs_find_daemon_by_euid(struct ecryptfs_daemon **daemon);
> +#endif
> int ecryptfs_init_kthread(void);
> void ecryptfs_destroy_kthread(void);
> int ecryptfs_privileged_open(struct file **lower_file,
> diff --git a/fs/ecryptfs/keystore.c b/fs/ecryptfs/keystore.c
> index 2333203..32bd806 100644
> --- a/fs/ecryptfs/keystore.c
> +++ b/fs/ecryptfs/keystore.c
> @@ -1168,7 +1168,7 @@ decrypt_pki_encrypted_session_key(struct ecryptfs_auth_tok *auth_tok,
> rc = ecryptfs_send_message(payload, payload_len, &msg_ctx);
> if (rc) {
> ecryptfs_printk(KERN_ERR, "Error sending message to "
> - "ecryptfsd\n");
> + "ecryptfsd: %d\n", rc);
> goto out;
> }
> rc = ecryptfs_wait_for_response(msg_ctx, &msg);
> @@ -1989,7 +1989,7 @@ pki_encrypt_session_key(struct key *auth_tok_key,
> rc = ecryptfs_send_message(payload, payload_len, &msg_ctx);
> if (rc) {
> ecryptfs_printk(KERN_ERR, "Error sending message to "
> - "ecryptfsd\n");
> + "ecryptfsd: %d\n", rc);
> goto out;
> }
> rc = ecryptfs_wait_for_response(msg_ctx, &msg);
> --
> 1.7.9.5
>
>
> --
> Kees Cook
> Chrome OS Security
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