Re: [PATCH 2/2] security: introduce kernel_module_from_file hook

[Mimi Zohar]

On Fri, 2012-09-07 at 11:38 -0700, Kees Cook wrote:
> Now that kernel module origins can be reasoned about, provide a hook to
> the LSMs to make policy decisions about the module file.
> 
> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
> Acked-by: Serge E. Hallyn <serge.hallyn@xxxxxxxxxxxxx>
> ---
>  include/linux/security.h |   13 +++++++++++++
>  kernel/module.c          |    9 +++++++++
>  security/capability.c    |    6 ++++++
>  security/security.c      |    5 +++++
>  4 files changed, 33 insertions(+), 0 deletions(-)
> 
> diff --git a/include/linux/security.h b/include/linux/security.h
> index 3dea6a9..368e539 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -693,6 +693,12 @@ static inline void security_free_mnt_opts(struct security_mnt_opts *opts)
>   *	userspace to load a kernel module with the given name.
>   *	@kmod_name name of the module requested by the kernel
>   *	Return 0 if successful.
> + * @kernel_module_from_file:
> + *	Load a kernel module from userspace.
> + *	@file contains the file structure pointing to the file containing
> + *	the kernel module to load. If the module is being loaded from a blob,
> + *	this argument will be NULL.
> + *	Return 0 if permission is granted.
>   * @task_fix_setuid:
>   *	Update the module's state after setting one or more of the user
>   *	identity attributes of the current process.  The @flags parameter
> @@ -1507,6 +1513,7 @@ struct security_operations {
>  	int (*kernel_act_as)(struct cred *new, u32 secid);
>  	int (*kernel_create_files_as)(struct cred *new, struct inode *inode);
>  	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,
>  				int flags);
>  	int (*task_setpgid) (struct task_struct *p, pid_t pgid);
> @@ -1764,6 +1771,7 @@ 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_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,
>  			     int flags);
>  int security_task_setpgid(struct task_struct *p, pid_t pgid);
> @@ -2277,6 +2285,11 @@ static inline int security_kernel_module_request(char *kmod_name)
>  	return 0;
>  }
> 
> +static inline int security_kernel_module_from_file(struct file *file)
> +{
> +	return 0;
> +}
> +
>  static inline int security_task_fix_setuid(struct cred *new,
>  					   const struct cred *old,
>  					   int flags)
> diff --git a/kernel/module.c b/kernel/module.c
> index c1e446e..0ad03c4 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -29,6 +29,7 @@
>  #include <linux/vmalloc.h>
>  #include <linux/elf.h>
>  #include <linux/proc_fs.h>
> +#include <linux/security.h>
>  #include <linux/seq_file.h>
>  #include <linux/syscalls.h>
>  #include <linux/fcntl.h>
> @@ -2430,6 +2431,10 @@ int copy_module_from_user(const void __user *umod, unsigned long len,
>  	if (info->len < sizeof(*(info->hdr)))
>  		return -ENOEXEC;
> 
> +	err = security_kernel_module_from_file(NULL);
> +	if (err)
> +		return err;
> +

For appraisal, having the security hook here is too early.  We need to
pass both the data and the signature.

>  	/* Suck in entire file: we'll want most of it. */
>  	info->hdr = vmalloc(info->len);
>  	if (!info->hdr)
> @@ -2468,6 +2473,10 @@ int copy_module_from_fd(int fd, struct load_info *info)
>  	if (err)
>  		goto out;
> 
> +	err = security_kernel_module_from_file(file);
> +	if (err)
> +		goto out;
> +

We probably want to pass the signature here as well, for those
filesystems that don't support extended attributes.

Mimi

>  	size = stat.size;
>  	info->hdr = vmalloc(size);
>  	if (!info->hdr) {
> diff --git a/security/capability.c b/security/capability.c
> index 61095df..8acb304 100644
> --- a/security/capability.c
> +++ b/security/capability.c
> @@ -395,6 +395,11 @@ static int cap_kernel_module_request(char *kmod_name)
>  	return 0;
>  }
> 
> +static int cap_kernel_module_from_file(struct file *file)
> +{
> +	return 0;
> +}
> +
>  static int cap_task_setpgid(struct task_struct *p, pid_t pgid)
>  {
>  	return 0;
> @@ -967,6 +972,7 @@ void __init security_fixup_ops(struct security_operations *ops)
>  	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_module_request);
> +	set_to_cap_if_null(ops, kernel_module_from_file);
>  	set_to_cap_if_null(ops, task_fix_setuid);
>  	set_to_cap_if_null(ops, task_setpgid);
>  	set_to_cap_if_null(ops, task_getpgid);
> diff --git a/security/security.c b/security/security.c
> index 860aeb3..f7f8695 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -799,6 +799,11 @@ int security_kernel_module_request(char *kmod_name)
>  	return security_ops->kernel_module_request(kmod_name);
>  }
> 
> +int security_kernel_module_from_file(struct file *file)
> +{
> +	return security_ops->kernel_module_from_file(file);
> +}
> +
>  int security_task_fix_setuid(struct cred *new, const struct cred *old,
>  			     int flags)
>  {


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