linux-kernel - Re: [PATCH v14 4/11] LSM: syscalls for current process attributes

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Message-ID: <20230907.eFie4boo3sei@digikod.net>
Date:   Thu, 7 Sep 2023 17:37:09 +0200
From:   Mickaël Salaün <mic@...ikod.net>
To:     Casey Schaufler <casey@...aufler-ca.com>
Cc:     Paul Moore <paul@...l-moore.com>,
        linux-security-module@...r.kernel.org, jmorris@...ei.org,
        serge@...lyn.com, 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
Subject: Re: [PATCH v14 4/11] LSM: syscalls for current process attributes

On Wed, Sep 06, 2023 at 04:48:04PM -0700, Casey Schaufler wrote:
> On 9/6/2023 4:22 PM, Paul Moore wrote:
> > On Aug 28, 2023 Casey Schaufler <casey@...aufler-ca.com> 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@...aufler-ca.com>
> >> Reviewed-by: Kees Cook <keescook@...omium.org>
> >> Reviewed-by: Serge Hallyn <serge@...lyn.com>
> >> Reviewed-by: John Johansen <john.johansen@...onical.com>
> >> ---

> >> +int security_getselfattr(unsigned int attr, struct lsm_ctx __user *uctx,
> >> +			 size_t __user *size, u32 flags)
> >> +{
> >> +	struct security_hook_list *hp;
> >> +	struct lsm_ctx lctx = { .id = LSM_ID_UNDEF, };
> >> +	u8 __user *base = (u8 __user *)uctx;
> >> +	size_t total = 0;
> >> +	size_t entrysize;
> >> +	size_t left;
> >> +	bool toobig = false;
> >> +	bool single = false;
> >> +	int count = 0;
> >> +	int rc;
> >> +
> >> +	if (attr == LSM_ATTR_UNDEF)
> >> +		return -EINVAL;
> >> +	if (size == NULL)
> >> +		return -EINVAL;
> >> +	if (get_user(left, size))
> >> +		return -EFAULT;
> >> +
> >> +	if (flags) {
> >> +		/*
> >> +		 * Only flag supported is LSM_FLAG_SINGLE
> >> +		 */
> >> +		if (flags & LSM_FLAG_SINGLE)
> >> +			return -EINVAL;
> > Should this be something like the following?
> >
> >   if (flags & ~LSM_FLAG_SINGLE)
> >     return -EINVAL;
> 
> Yes. I have a fix ready. There are a couple other touch-ups, too.

This is already part of patch 11. It should be squashed here.