[PATCH v15 05/11] LSM: Create lsm_list_modules system call

[Mickaël Salaün]

On Tue, Sep 12, 2023 at 01:56:50PM -0700, Casey Schaufler wrote:
> Create a system call to report the list of Linux Security Modules
> that are active on the system. The list is provided as an array
> of LSM ID numbers.
> 
> The calling application can use this list determine what LSM
> specific actions it might take. That might include choosing an
> output format, determining required privilege or bypassing
> security module specific behavior.
> 
> Signed-off-by: Casey Schaufler <casey at schaufler-ca.com>
> Reviewed-by: Kees Cook <keescook at chromium.org>
> Reviewed-by: Serge Hallyn <serge at hallyn.com>
> Reviewed-by: John Johansen <john.johansen at canonical.com>

Reviewed-by: Mickaël Salaün <mic at digikod.net>

> ---
>  Documentation/userspace-api/lsm.rst |  3 +++
>  include/linux/syscalls.h            |  1 +
>  kernel/sys_ni.c                     |  1 +
>  security/lsm_syscalls.c             | 39 +++++++++++++++++++++++++++++
>  4 files changed, 44 insertions(+)
> 
> diff --git a/Documentation/userspace-api/lsm.rst b/Documentation/userspace-api/lsm.rst
> index f8499f3e2826..a76da373841b 100644
> --- a/Documentation/userspace-api/lsm.rst
> +++ b/Documentation/userspace-api/lsm.rst
> @@ -63,6 +63,9 @@ Get the specified security attributes of the current process
>  .. kernel-doc:: security/lsm_syscalls.c
>      :identifiers: sys_lsm_get_self_attr
>  
> +.. kernel-doc:: security/lsm_syscalls.c
> +    :identifiers: sys_lsm_list_modules
> +
>  Additional documentation
>  ========================
>  
> diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
> index 8637287bd39d..323ef5e2667d 100644
> --- a/include/linux/syscalls.h
> +++ b/include/linux/syscalls.h
> @@ -945,6 +945,7 @@ asmlinkage long sys_lsm_get_self_attr(unsigned int attr, struct lsm_ctx *ctx,
>  				      size_t *size, __u32 flags);
>  asmlinkage long sys_lsm_set_self_attr(unsigned int attr, struct lsm_ctx *ctx,
>  				      size_t size, __u32 flags);
> +asmlinkage long sys_lsm_list_modules(u64 *ids, size_t *size, u32 flags);
>  
>  /*
>   * Architecture-specific system calls
> diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
> index f81f2468c0ce..738ca470fcce 100644
> --- a/kernel/sys_ni.c
> +++ b/kernel/sys_ni.c
> @@ -172,6 +172,7 @@ COND_SYSCALL(fadvise64_64);
>  COND_SYSCALL_COMPAT(fadvise64_64);
>  COND_SYSCALL(lsm_get_self_attr);
>  COND_SYSCALL(lsm_set_self_attr);
> +COND_SYSCALL(lsm_list_modules);
>  
>  /* CONFIG_MMU only */
>  COND_SYSCALL(swapon);
> diff --git a/security/lsm_syscalls.c b/security/lsm_syscalls.c
> index 226ae80d9683..329aaca5efc0 100644
> --- a/security/lsm_syscalls.c
> +++ b/security/lsm_syscalls.c
> @@ -55,3 +55,42 @@ SYSCALL_DEFINE4(lsm_get_self_attr, unsigned int, attr, struct lsm_ctx __user *,
>  {
>  	return security_getselfattr(attr, ctx, size, flags);
>  }
> +
> +/**
> + * sys_lsm_list_modules - Return a list of the active security modules
> + * @ids: the LSM module ids
> + * @size: pointer to size of @ids, updated on return
> + * @flags: reserved for future use, must be zero
> + *
> + * Returns a list of the active LSM ids. On success this function
> + * returns the number of @ids array elements. This value may be zero
> + * if there are no LSMs active. If @size is insufficient to contain
> + * the return data -E2BIG is returned and @size is set to the minimum
> + * required size. In all other cases a negative value indicating the
> + * error is returned.
> + */
> +SYSCALL_DEFINE3(lsm_list_modules, u64 __user *, ids, size_t __user *, size,
> +		u32, flags)
> +{
> +	size_t total_size = lsm_active_cnt * sizeof(*ids);
> +	size_t usize;
> +	int i;
> +
> +	if (flags)
> +		return -EINVAL;
> +
> +	if (get_user(usize, size))
> +		return -EFAULT;
> +
> +	if (put_user(total_size, size) != 0)
> +		return -EFAULT;
> +
> +	if (usize < total_size)
> +		return -E2BIG;
> +
> +	for (i = 0; i < lsm_active_cnt; i++)
> +		if (put_user(lsm_idlist[i]->id, ids++))
> +			return -EFAULT;
> +
> +	return lsm_active_cnt;
> +}
> -- 
> 2.41.0
>