linux-kernel - Re: [PATCH v1 6/8] LSM: lsm_self_attr syscall for LSM self attributes

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Date:   Wed, 26 Oct 2022 08:03:29 +0200
From:   Greg KH <greg@...ah.com>
To:     Casey Schaufler <casey@...aufler-ca.com>
Cc:     casey.schaufler@...el.com, paul@...l-moore.com,
        linux-security-module@...r.kernel.org, jmorris@...ei.org,
        keescook@...omium.org, john.johansen@...onical.com,
        penguin-kernel@...ove.sakura.ne.jp, stephen.smalley.work@...il.com,
        linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
        mic@...ikod.net
Subject: Re: [PATCH v1 6/8] LSM: lsm_self_attr syscall for LSM self attributes

On Tue, Oct 25, 2022 at 11:45:17AM -0700, Casey Schaufler wrote:
> Create a system call lsm_self_attr() to provide the security
> module maintained attributes of the current process. Historically
> these attributes have been exposed to user space via entries in
> procfs under /proc/self/attr.
> 
> Attributes are provided as a collection of lsm_ctx structures
> which are placed into a user supplied buffer. Each structure
> identifys the security module providing the attribute, which
> of the possible attributes is provided, the size of the
> attribute, and finally the attribute value. The format of the
> attribute value is defined by the security module, but will
> always be \0 terminated. The ctx_len value will be larger than
> strlen(ctx).
> 
>         ------------------------------
>         | unsigned int id            |
>         ------------------------------
>         | unsigned int flags         |
>         ------------------------------
>         | __kernel_size_t ctx_len    |
>         ------------------------------
>         | unsigned char ctx[ctx_len] |
>         ------------------------------
>         | unsigned int id            |
>         ------------------------------
>         | unsigned int flags         |
>         ------------------------------
>         | __kernel_size_t ctx_len    |
>         ------------------------------
>         | unsigned char ctx[ctx_len] |
>         ------------------------------
> 
> Signed-off-by: Casey Schaufler <casey@...aufler-ca.com>
> ---
>  include/linux/syscalls.h |   2 +
>  include/uapi/linux/lsm.h |  21 ++++++
>  kernel/sys_ni.c          |   3 +
>  security/Makefile        |   1 +
>  security/lsm_syscalls.c  | 156 +++++++++++++++++++++++++++++++++++++++
>  5 files changed, 183 insertions(+)
>  create mode 100644 security/lsm_syscalls.c
> 
> diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
> index a34b0f9a9972..2d9033e9e5a0 100644
> --- a/include/linux/syscalls.h
> +++ b/include/linux/syscalls.h
> @@ -71,6 +71,7 @@ struct clone_args;
>  struct open_how;
>  struct mount_attr;
>  struct landlock_ruleset_attr;
> +struct lsm_cxt;
>  enum landlock_rule_type;
>  
>  #include <linux/types.h>
> @@ -1056,6 +1057,7 @@ asmlinkage long sys_memfd_secret(unsigned int flags);
>  asmlinkage long sys_set_mempolicy_home_node(unsigned long start, unsigned long len,
>  					    unsigned long home_node,
>  					    unsigned long flags);
> +asmlinkage long sys_lsm_self_attr(struct lsm_ctx *ctx, size_t *size, int flags);
>  
>  /*
>   * Architecture-specific system calls
> diff --git a/include/uapi/linux/lsm.h b/include/uapi/linux/lsm.h
> index 61e13b1b9ece..1d27fb5b7746 100644
> --- a/include/uapi/linux/lsm.h
> +++ b/include/uapi/linux/lsm.h
> @@ -9,6 +9,27 @@
>  #ifndef _UAPI_LINUX_LSM_H
>  #define _UAPI_LINUX_LSM_H
>  
> +#include <linux/types.h>
> +#include <linux/unistd.h>
> +
> +/**
> + * struct lsm_ctx - LSM context
> + * @id: the LSM id number, see LSM_ID_XXX
> + * @flags: context specifier and LSM specific flags
> + * @ctx_len: the size of @ctx
> + * @ctx: the LSM context, a nul terminated string
> + *
> + * @ctx in a nul terminated string.
> + *	(strlen(@ctx) < @ctx_len) is always true.
> + *	(strlen(@ctx) == @ctx_len + 1) is not guaranteed.
> + */
> +struct lsm_ctx {
> +	unsigned int		id;
> +	unsigned int		flags;
> +	__kernel_size_t		ctx_len;
> +	unsigned char		ctx[];

Please use data types that are allowed to cross the user/kernel boundry
in a safe way.  That would mean this would use __u64 instead of unsigned
int, and __u8 instead of unsigned char.

thanks,

greg k-h