Re: [PATCH v13 04/11] LSM: syscalls for current process attributes

[Mickaël Salaün]

On Wed, Aug 02, 2023 at 10:44:27AM -0700, Casey Schaufler wrote:
> Create a system call lsm_get_self_attr() to provide the security
> module maintained attributes of the current process.
> Create a system call lsm_set_self_attr() to set a security
> module maintained attribute of the current process.
> Historically these attributes have been exposed to user space via
> entries in procfs under /proc/self/attr.
> 
> The attribute value is provided in a lsm_ctx structure. The structure
> identifies the size of the attribute, and the attribute value. The format
> of the attribute value is defined by the security module. A flags field
> is included for LSM specific information. It is currently unused and must
> be 0. The total size of the data, including the lsm_ctx structure and any
> padding, is maintained as well.
> 
> struct lsm_ctx {
>         __u64 id;
>         __u64 flags;
>         __u64 len;
>         __u64 ctx_len;
>         __u8 ctx[];
> };
> 
> Two new LSM hooks are used to interface with the LSMs.
> security_getselfattr() collects the lsm_ctx values from the
> LSMs that support the hook, accounting for space requirements.
> security_setselfattr() identifies which LSM the attribute is
> intended for and passes it along.
> 
> Signed-off-by: Casey Schaufler <casey@xxxxxxxxxxxxxxxx>
> Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
> Reviewed-by: Serge Hallyn <serge@xxxxxxxxxx>
> ---
>  Documentation/userspace-api/lsm.rst |  70 ++++++++++++++++
>  include/linux/lsm_hook_defs.h       |   4 +
>  include/linux/lsm_hooks.h           |   1 +
>  include/linux/security.h            |  19 +++++
>  include/linux/syscalls.h            |   5 ++
>  include/uapi/linux/lsm.h            |  90 ++++++++++++++++++++
>  kernel/sys_ni.c                     |   2 +
>  security/Makefile                   |   1 +
>  security/lsm_syscalls.c             |  55 ++++++++++++
>  security/security.c                 | 125 ++++++++++++++++++++++++++++
>  10 files changed, 372 insertions(+)
>  create mode 100644 Documentation/userspace-api/lsm.rst
>  create mode 100644 include/uapi/linux/lsm.h
>  create mode 100644 security/lsm_syscalls.c

> +/**
> + * security_setselfattr - Set an LSM attribute on the current process.
> + * @attr: which attribute to set
> + * @ctx: the user-space source for the information
> + * @size: the size of the data
> + * @flags: reserved for future use, must be 0
> + *
> + * Set an LSM attribute for the current process. The LSM, attribute
> + * and new value are included in @ctx.
> + *
> + * Returns 0 on success, -EINVAL if the input is inconsistent, -EFAULT
> + * if the user buffer is inaccessible or an LSM specific failure.
> + */
> +int security_setselfattr(unsigned int attr, struct lsm_ctx __user *ctx,
> +			 size_t size, u32 flags)
> +{
> +	struct security_hook_list *hp;
> +	struct lsm_ctx *lctx;
> +	int rc = LSM_RET_DEFAULT(setselfattr);
> +
> +	if (flags)
> +		return -EINVAL;
> +	if (size < sizeof(*ctx))
> +		return -EINVAL;
> +
> +	lctx = kmalloc(size, GFP_KERNEL);
> +	if (lctx == NULL)
> +		return -ENOMEM;
> +
> +	if (copy_from_user(&lctx, ctx, size))

This should be copy_from_user(lctx, ctx, size)

> +		return -EFAULT;
> +
> +	if (size < lctx->len || size < lctx->ctx_len + sizeof(ctx) ||
> +	    lctx->len < lctx->ctx_len + sizeof(ctx))
> +		return -EINVAL;
> +
> +	hlist_for_each_entry(hp, &security_hook_heads.setselfattr, list)
> +		if ((hp->lsmid->id) == lctx->id) {
> +			rc = hp->hook.setselfattr(attr, lctx, size, flags);
> +			break;
> +		}
> +
> +	kfree(lctx);
> +	return rc;
> +}
> +
>  /**
>   * security_getprocattr() - Read an attribute for a task
>   * @p: the task
> -- 
> 2.41.0
>