linux/security/commoncap.c

/* Common capabilities, needed by capability.o.
 *
 *	This program is free software; you can redistribute it and/or modify
 *	it under the terms of the GNU General Public License as published by
 *	the Free Software Foundation; either version 2 of the License, or
 *	(at your option) any later version.
 *
 */

#include <linux/capability.h>
#include <linux/audit.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/lsm_hooks.h>
#include <linux/file.h>
#include <linux/mm.h>
#include <linux/mman.h>
#include <linux/pagemap.h>
#include <linux/swap.h>
#include <linux/skbuff.h>
#include <linux/netlink.h>
#include <linux/ptrace.h>
#include <linux/xattr.h>
#include <linux/hugetlb.h>
#include <linux/mount.h>
#include <linux/sched.h>
#include <linux/prctl.h>
#include <linux/securebits.h>
#include <linux/user_namespace.h>
#include <linux/binfmts.h>
#include <linux/personality.h>

/*
 * If a non-root user executes a setuid-root binary in
 * !secure(SECURE_NOROOT) mode, then we raise capabilities.
 * However if fE is also set, then the intent is for only
 * the file capabilities to be applied, and the setuid-root
 * bit is left on either to change the uid (plausible) or
 * to get full privilege on a kernel without file capabilities
 * support.  So in that case we do not raise capabilities.
 *
 * Warn if that happens, once per boot.
 */
static void warn_setuid_and_fcaps_mixed(const char *fname)
{
	static int warned;
	if (!warned) {
		printk(KERN_INFO "warning: `%s' has both setuid-root and"
			" effective capabilities. Therefore not raising all"
			" capabilities.\n", fname);
		warned = 1;
	}
}

/**
 * cap_capable - Determine whether a task has a particular effective capability
 * @cred: The credentials to use
 * @ns:  The user namespace in which we need the capability
 * @cap: The capability to check for
 * @audit: Whether to write an audit message or not
 *
 * Determine whether the nominated task has the specified capability amongst
 * its effective set, returning 0 if it does, -ve if it does not.
 *
 * NOTE WELL: cap_has_capability() cannot be used like the kernel's capable()
 * and has_capability() functions.  That is, it has the reverse semantics:
 * cap_has_capability() returns 0 when a task has a capability, but the
 * kernel's capable() and has_capability() returns 1 for this case.
 */
int cap_capable(const struct cred *cred, struct user_namespace *targ_ns,
		int cap, int audit)
{
	struct user_namespace *ns = targ_ns;

	/* See if cred has the capability in the target user namespace
	 * by examining the target user namespace and all of the target
	 * user namespace's parents.
	 */
	for (;;) {
		/* Do we have the necessary capabilities? */
		if (ns == cred->user_ns)
			return cap_raised(cred->cap_effective, cap) ? 0 : -EPERM;

		/*
		 * If we're already at a lower level than we're looking for,
		 * we're done searching.
		 */
		if (ns->level <= cred->user_ns->level)
			return -EPERM;

		/* 
		 * The owner of the user namespace in the parent of the
		 * user namespace has all caps.
		 */
		if ((ns->parent == cred->user_ns) && uid_eq(ns->owner, cred->euid))
			return 0;

		/*
		 * If you have a capability in a parent user ns, then you have
		 * it over all children user namespaces as well.
		 */
		ns = ns->parent;
	}

	/* We never get here */
}

/**
 * cap_settime - Determine whether the current process may set the system clock
 * @ts: The time to set
 * @tz: The timezone to set
 *
 * Determine whether the current process may set the system clock and timezone
 * information, returning 0 if permission granted, -ve if denied.
 */
int cap_settime(const struct timespec64 *ts, const struct timezone *tz)
{
	if (!capable(CAP_SYS_TIME))
		return -EPERM;
	return 0;
}

/**
 * cap_ptrace_access_check - Determine whether the current process may access
 *			   another
 * @child: The process to be accessed
 * @mode: The mode of attachment.
 *
 * If we are in the same or an ancestor user_ns and have all the target
 * task's capabilities, then ptrace access is allowed.
 * If we have the ptrace capability to the target user_ns, then ptrace
 * access is allowed.
 * Else denied.
 *
 * Determine whether a process may access another, returning 0 if permission
 * granted, -ve if denied.
 */
int cap_ptrace_access_check(struct task_struct *child, unsigned int mode)
{
	int ret = 0;
	const struct cred *cred, *child_cred;
	const kernel_cap_t *caller_caps;

	rcu_read_lock();
	cred = current_cred();
	child_cred = __task_cred(child);
	if (mode & PTRACE_MODE_FSCREDS)
		caller_caps = &cred->cap_effective;
	else
		caller_caps = &cred->cap_permitted;
	if (cred->user_ns == child_cred->user_ns &&
	    cap_issubset(child_cred->cap_permitted, *caller_caps))
		goto out;
	if (ns_capable(child_cred->user_ns, CAP_SYS_PTRACE))
		goto out;
	ret = -EPERM;
out:
	rcu_read_unlock();
	return ret;
}

/**
 * cap_ptrace_traceme - Determine whether another process may trace the current
 * @parent: The task proposed to be the tracer
 *
 * If parent is in the same or an ancestor user_ns and has all current's
 * capabilities, then ptrace access is allowed.
 * If parent has the ptrace capability to current's user_ns, then ptrace
 * access is allowed.
 * Else denied.
 *
 * Determine whether the nominated task is permitted to trace the current
 * process, returning 0 if permission is granted, -ve if denied.
 */
int cap_ptrace_traceme(struct task_struct *parent)
{
	int ret = 0;
	const struct cred *cred, *child_cred;

	rcu_read_lock();
	cred = __task_cred(parent);
	child_cred = current_cred();
	if (cred->user_ns == child_cred->user_ns &&
	    cap_issubset(child_cred->cap_permitted, cred->cap_permitted))
		goto out;
	if (has_ns_capability(parent, child_cred->user_ns, CAP_SYS_PTRACE))
		goto out;
	ret = -EPERM;
out:
	rcu_read_unlock();
	return ret;
}

/**
 * cap_capget - Retrieve a task's capability sets
 * @target: The task from which to retrieve the capability sets
 * @effective: The place to record the effective set
 * @inheritable: The place to record the inheritable set
 * @permitted: The place to record the permitted set
 *
 * This function retrieves the capabilities of the nominated task and returns
 * them to the caller.
 */
int cap_capget(struct task_struct *target, kernel_cap_t *effective,
	       kernel_cap_t *inheritable, kernel_cap_t *permitted)
{
	const struct cred *cred;

	/* Derived from kernel/capability.c:sys_capget. */
	rcu_read_lock();
	cred = __task_cred(target);
	*effective   = cred->cap_effective;
	*inheritable = cred->cap_inheritable;
	*permitted   = cred->cap_permitted;
	rcu_read_unlock();
	return 0;
}

/*
 * Determine whether the inheritable capabilities are limited to the old
 * permitted set.  Returns 1 if they are limited, 0 if they are not.
 */
static inline int cap_inh_is_capped(void)
{

	/* they are so limited unless the current task has the CAP_SETPCAP
	 * capability
	 */
	if (cap_capable(current_cred(), current_cred()->user_ns,
			CAP_SETPCAP, SECURITY_CAP_AUDIT) == 0)
		return 0;
	return 1;
}

/**
 * cap_capset - Validate and apply proposed changes to current's capabilities
 * @new: The proposed new credentials; alterations should be made here
 * @old: The current task's current credentials
 * @effective: A pointer to the proposed new effective capabilities set
 * @inheritable: A pointer to the proposed new inheritable capabilities set
 * @permitted: A pointer to the proposed new permitted capabilities set
 *
 * This function validates and applies a proposed mass change to the current
 * process's capability sets.  The changes are made to the proposed new
 * credentials, and assuming no error, will be committed by the caller of LSM.
 */
int cap_capset(struct cred *new,
	       const struct cred *old,
	       const kernel_cap_t *effective,
	       const kernel_cap_t *inheritable,
	       const kernel_cap_t *permitted)
{
	if (cap_inh_is_capped() &&
	    !cap_issubset(*inheritable,
			  cap_combine(old->cap_inheritable,
				      old->cap_permitted)))