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SubjectRe: [PATCH v6 04/11] LSM: syscalls for current process attributes
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On 22/02/2023 21:08, 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
> identifys 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@schaufler-ca.com>
> ---
> Documentation/userspace-api/lsm.rst | 15 ++++
> include/linux/lsm_hook_defs.h | 4 ++
> include/linux/lsm_hooks.h | 9 +++
> include/linux/security.h | 19 +++++
> include/linux/syscalls.h | 4 ++
> include/uapi/linux/lsm.h | 33 +++++++++
> kernel/sys_ni.c | 4 ++
> security/Makefile | 1 +
> security/lsm_syscalls.c | 104 ++++++++++++++++++++++++++++
> security/security.c | 82 ++++++++++++++++++++++
> 10 files changed, 275 insertions(+)
> create mode 100644 security/lsm_syscalls.c
>

[...]

> +/**
> + * security_setselfattr - Set an LSM attribute on the current process.
> + * @attr: which attribute to return
> + * @ctx: the user-space source for the information
> + * @size: the size of the data
> + *
> + * Set an LSM attribute for the current process. The LSM, attribute
> + * and new value are included in @ctx.
> + *
> + * Returns 0 on seccess, an LSM specific value on failure.
> + */
> +int security_setselfattr(u64 __user attr, struct lsm_ctx __user *ctx,
> + size_t __user size)
> +{
> + struct security_hook_list *hp;
> + struct lsm_ctx lctx;
> +
> + if (size < sizeof(*ctx))

If the lsm_ctx struct could grow in the future, we should check the size
of the struct to the last field for compatibility reasons, see
Landlock's copy_min_struct_from_user().


> + return -EINVAL;
> + if (copy_from_user(&lctx, ctx, sizeof(*ctx)))
> + return -EFAULT;
> +
> + hlist_for_each_entry(hp, &security_hook_heads.setselfattr, list)
> + if ((hp->lsmid->id) == lctx.id)
> + return hp->hook.setselfattr(attr, ctx, size);
> +
> + return LSM_RET_DEFAULT(setselfattr);
> +}
> +
> int security_getprocattr(struct task_struct *p, int lsmid, const char *name,
> char **value)
> {

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