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SubjectRe: [PATCH v5 next 1/5] modules:capabilities: add request_module_cap()
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Date
Hi,

Mostly typos/spellos...


On 11/27/2017 09:18 AM, Djalal Harouni wrote:
> Cc: Serge Hallyn <serge@hallyn.com>
> Cc: Andy Lutomirski <luto@kernel.org>
> Suggested-by: Rusty Russell <rusty@rustcorp.com.au>
> Suggested-by: Kees Cook <keescook@chromium.org>
> Signed-off-by: Djalal Harouni <tixxdz@gmail.com>
> ---
> include/linux/kmod.h | 65 ++++++++++++++++++++++++++++++++++++++++++-----
> include/linux/lsm_hooks.h | 6 ++++-
> include/linux/security.h | 7 +++--
> kernel/kmod.c | 29 ++++++++++++++++-----
> security/security.c | 6 +++--
> security/selinux/hooks.c | 3 ++-
> 6 files changed, 97 insertions(+), 19 deletions(-)
>
> diff --git a/include/linux/kmod.h b/include/linux/kmod.h
> index 40c89ad..ccd6a1c 100644
> --- a/include/linux/kmod.h
> +++ b/include/linux/kmod.h
> @@ -33,16 +33,67 @@

> +/**
> + * request_module Try to load a kernel module
> + *
> + * Automatically loads the request module.
> + *
> + * @mod...: The module name
> + */

what are the "..." for? what do they do here?

> +#define request_module(mod...) __request_module(true, -1, NULL, mod)
> +
> +#define request_module_nowait(mod...) __request_module(false, -1, NULL, mod)
> +
> +/**
> + * request_module_cap Load kernel module only if the required capability is set
> + *
> + * Automatically load a module if the required capability is set and it
> + * corresponds to the appropriate subsystem that is indicated by prefix.
> + *
> + * This allows to load aliased modules like 'netdev-%s' with CAP_NET_ADMIN.
> + *
> + * ex:
> + * request_module_cap(CAP_NET_ADMIN, "netdev", "%s", mod);
> + *
> + * @required_cap: Required capability to load the module
> + * @prefix: The module prefix if any, otherwise NULL
> + * @fmt: printf style format string for the name of the module with its
> + * arguments if any
> + *
> + * If '@required_cap' is positive, the security subsystem will check if
> + * '@prefix' is set and if caller has the required capability then the
> + * operation is allowed.
> + * The security subsystem can not make assumption about the boundaries
> + * of other subsystems, it is their responsability to make a call with

responsibility

> + * the right capability and module alias.
> + *
> + * If '@required_cap' is positive and '@prefix' is NULL then we assume
> + * that the '@required_cap' is CAP_SYS_MODULE.
> + *
> + * If '@required_cap' is negative then there are no permission checks, this
> + * is the equivalent to request_module() function.
> + *
> + * This function trust callers to pass the right capability with the

trusts

> + * appropriate prefix.
> + *
> + * Note: the permission checks may still fail, even if the required
> + * capability is negative, this is due to module loading restrictions

negative; this

> + * that are controlled by the enduser.
> + */
> +#define request_module_cap(required_cap, prefix, fmt...) \
> + __request_module(true, required_cap, prefix, fmt)
> +
> #endif /* __LINUX_KMOD_H__ */
> diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
> index 7161d8e..d898bd0 100644
> --- a/include/linux/lsm_hooks.h
> +++ b/include/linux/lsm_hooks.h
> @@ -571,6 +571,9 @@
> * Ability to trigger the kernel to automatically upcall to userspace for
> * userspace to load a kernel module with the given name.
> * @kmod_name name of the module requested by the kernel
> + * @required_cap If positive, the required capability to automatically load
> + * the correspondig kernel module.

corresponding

> + * @prefix The prefix of the module if any. Can be NULL.
> * Return 0 if successful.
> * @kernel_read_file:
> * Read a file specified by userspace.

> diff --git a/kernel/kmod.c b/kernel/kmod.c
> index bc6addd..679d401 100644
> --- a/kernel/kmod.c
> +++ b/kernel/kmod.c
> @@ -109,6 +109,8 @@ static int call_modprobe(char *module_name, int wait)
> /**
> * __request_module - try to load a kernel module
> * @wait: wait (or not) for the operation to complete
> + * @required_cap: required capability to load the module
> + * @prefix: module prefix if any otherwise NULL
> * @fmt: printf style format string for the name of the module
> * @...: arguments as specified in the format string
> *
> @@ -119,14 +121,20 @@ static int call_modprobe(char *module_name, int wait)
> * must check that the service they requested is now available not blindly
> * invoke it.
> *
> - * If module auto-loading support is disabled then this function
> - * becomes a no-operation.
> + * If "required_cap" is positive, The security subsystem will trust the caller

the

> + * that if it has "required_cap" then it may allow to load some modules that
> + * have a specific alias.
> + *
> + * If module auto-loading support is disabled by clearing the modprobe path
> + * then this function becomes a no-operation.
> */
> -int __request_module(bool wait, const char *fmt, ...)
> +int __request_module(bool wait, int required_cap,
> + const char *prefix, const char *fmt, ...)
> {
> va_list args;
> char module_name[MODULE_NAME_LEN];
> int ret;
> + int len = 0;
>
> /*
> * We don't allow synchronous module loading from async. Module
> @@ -139,13 +147,22 @@ int __request_module(bool wait, const char *fmt, ...)
> if (!modprobe_path[0])
> return 0;
>
> + /*
> + * Lets attach the prefix to the module name

Let's
but better:
* Attach the prefix to the module name

> + */
> + if (prefix != NULL && *prefix != '\0') {
> + len += snprintf(module_name, MODULE_NAME_LEN, "%s-", prefix);
> + if (len >= MODULE_NAME_LEN)
> + return -ENAMETOOLONG;
> + }
> +
> va_start(args, fmt);
> - ret = vsnprintf(module_name, MODULE_NAME_LEN, fmt, args);
> + ret = vsnprintf(module_name + len, MODULE_NAME_LEN - len, fmt, args);
> va_end(args);
> - if (ret >= MODULE_NAME_LEN)
> + if (ret >= MODULE_NAME_LEN - len)
> return -ENAMETOOLONG;
>
> - ret = security_kernel_module_request(module_name);
> + ret = security_kernel_module_request(module_name, required_cap, prefix);
> if (ret)
> return ret;
>


--
~Randy

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