Re: [PATCH 3/7] security: introduce kernel_fw_from_file hook

Mimi Zohar
2014-07-18T17:11:51Z

On Mon, 2014-07-14 at 14:38 -0700, Kees Cook wrote:
> In order to validate the contents of firmware being loaded, there must be
> a hook to evaluate any loaded firmware that wasn't built into the kernel
> itself. Without this, there is a risk that a root user could load malicious
> firmware designed to mount an attack against kernel memory (e.g. via DMA).
>
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
> include/linux/security.h | 16 ++++++++++++++++
> security/capability.c | 6 ++++++
> security/security.c | 6 ++++++
> 3 files changed, 28 insertions(+)
>
> diff --git a/include/linux/security.h b/include/linux/security.h
> index 9c6b9722ff48..dbb80b3e99d7 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -702,6 +702,14 @@ static inline void security_free_mnt_opts(struct security_mnt_opts *opts)
> * @inode points to the inode to use as a reference.
> * The current task must be the one that nominated @inode.
> * Return 0 if successful.
> + * @kernel_fw_from_file:
> + * Load firmware from userspace.
> + * @file contains the file structure pointing to the file containing
> + * the firmware to load. If the module is being loaded from a blob,
> + * this argument will be NULL.
> + * @buf pointer to buffer containing firmware contents.
> + * @size length of the firmware contents.
> + * Return 0 if permission is granted.
> * @kernel_module_request:
> * Ability to trigger the kernel to automatically upcall to userspace for
> * userspace to load a kernel module with the given name.
> @@ -1565,6 +1573,7 @@ struct security_operations {
> void (*cred_transfer)(struct cred *new, const struct cred *old);
> int (*kernel_act_as)(struct cred *new, u32 secid);
> int (*kernel_create_files_as)(struct cred *new, struct inode *inode);
> + int (*kernel_fw_from_file)(struct file *file, char *buf, size_t size);
> int (*kernel_module_request)(char *kmod_name);
> int (*kernel_module_from_file)(struct file *file);
> int (*task_fix_setuid) (struct cred *new, const struct cred *old,
> @@ -1837,6 +1846,7 @@ int security_prepare_creds(struct cred *new, const struct cred *old, gfp_t gfp);
> void security_transfer_creds(struct cred *new, const struct cred *old);
> int security_kernel_act_as(struct cred *new, u32 secid);
> int security_kernel_create_files_as(struct cred *new, struct inode *inode);
> +int security_kernel_fw_from_file(struct file *file, char *buf, size_t size);
> int security_kernel_module_request(char *kmod_name);
> int security_kernel_module_from_file(struct file *file);
> int security_task_fix_setuid(struct cred *new, const struct cred *old,
> @@ -2363,6 +2373,12 @@ static inline int security_kernel_create_files_as(struct cred *cred,
> return 0;
> }
>
> +static inline int security_kernel_fw_from_file(struct file *file,
> + char *buf, size_t size)
> +{
> + return 0;
> +}
> +
> static inline int security_kernel_module_request(char *kmod_name)
> {
> return 0;
> diff --git a/security/capability.c b/security/capability.c
> index e76373de3129..a74fde6a7468 100644
> --- a/security/capability.c
> +++ b/security/capability.c
> @@ -401,6 +401,11 @@ static int cap_kernel_create_files_as(struct cred *new, struct inode *inode)
> return 0;
> }
>
> +static int cap_kernel_fw_from_file(struct file *file, char *buf, size_t size)
> +{
> + return 0;
> +}
> +
> static int cap_kernel_module_request(char *kmod_name)
> {
> return 0;
> @@ -1015,6 +1020,7 @@ void __init security_fixup_ops(struct security_operations *ops)
> set_to_cap_if_null(ops, cred_transfer);
> set_to_cap_if_null(ops, kernel_act_as);
> set_to_cap_if_null(ops, kernel_create_files_as);
> + set_to_cap_if_null(ops, kernel_fw_from_file);
> set_to_cap_if_null(ops, kernel_module_request);
> set_to_cap_if_null(ops, kernel_module_from_file);
> set_to_cap_if_null(ops, task_fix_setuid);
> diff --git a/security/security.c b/security/security.c
> index 31614e9e96e5..35d37d0f0d49 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -845,6 +845,12 @@ int security_kernel_create_files_as(struct cred *new, struct inode *inode)
> return security_ops->kernel_create_files_as(new, inode);
> }
>
> +int security_kernel_fw_from_file(struct file *file, char *buf, size_t size)
> +{
> + return security_ops->kernel_fw_from_file(file, buf, size);
> +}
> +EXPORT_SYMBOL_GPL(security_kernel_fw_from_file);
> +

Nice set of patches! I'll need to send you a patch to call IMA.

Mimi

> int security_kernel_module_request(char *kmod_name)
> {
> return security_ops->kernel_module_request(kmod_name);