userns: security: make capabilities relative to the user namespace

[GitHub/LineageOS/android_kernel_motorola_exynos9610.git] / 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/security.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>

/*
 * 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;
        }
}

int cap_netlink_send(struct sock *sk, struct sk_buff *skb)
{
        return 0;
}

int cap_netlink_recv(struct sk_buff *skb, int cap)
{
        if (!cap_raised(current_cap(), cap))
                return -EPERM;
        return 0;
}
EXPORT_SYMBOL(cap_netlink_recv);

/**
 * cap_capable - Determine whether a task has a particular effective capability
 * @tsk: The task to query
 * @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(struct task_struct *tsk, const struct cred *cred,
                struct user_namespace *targ_ns, int cap, int audit)
{
        for (;;) {
                /* The creator of the user namespace has all caps. */
                if (targ_ns != &init_user_ns && targ_ns->creator == cred->user)
                        return 0;

                /* Do we have the necessary capabilities? */
                if (targ_ns == cred->user->user_ns)
                        return cap_raised(cred->cap_effective, cap) ? 0 : -EPERM;

                /* Have we tried all of the parent namespaces? */
                if (targ_ns == &init_user_ns)
                        return -EPERM;

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

        /* 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 timespec *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.
 *
 * 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;

        rcu_read_lock();
        if (!cap_issubset(__task_cred(child)->cap_permitted,
                          current_cred()->cap_permitted) &&
            !capable(CAP_SYS_PTRACE))
                ret = -EPERM;
        rcu_read_unlock();
        return ret;
}

/**
 * cap_ptrace_traceme - Determine whether another process may trace the current
 * @parent: The task proposed to be the tracer
 *
 * 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;

        rcu_read_lock();
        if (!cap_issubset(current_cred()->cap_permitted,
                          __task_cred(parent)->cap_permitted) &&
            !has_capability(parent, CAP_SYS_PTRACE))
                ret = -EPERM;
        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, current_cred(),
                        current_cred()->user->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)))
                /* incapable of using this inheritable set */
                return -EPERM;

        if (!cap_issubset(*inheritable,
                          cap_combine(old->cap_inheritable,
                                      old->cap_bset)))
                /* no new pI capabilities outside bounding set */
                return -EPERM;

        /* verify restrictions on target's new Permitted set */
        if (!cap_issubset(*permitted, old->cap_permitted))
                return -EPERM;

        /* verify the _new_Effective_ is a subset of the _new_Permitted_ */
        if (!cap_issubset(*effective, *permitted))
                return -EPERM;

        new->cap_effective   = *effective;
        new->cap_inheritable = *inheritable;
        new->cap_permitted   = *permitted;
        return 0;
}

/*
 * Clear proposed capability sets for execve().
 */
static inline void bprm_clear_caps(struct linux_binprm *bprm)
{
        cap_clear(bprm->cred->cap_permitted);
        bprm->cap_effective = false;
}

/**
 * cap_inode_need_killpriv - Determine if inode change affects privileges
 * @dentry: The inode/dentry in being changed with change marked ATTR_KILL_PRIV
 *
 * Determine if an inode having a change applied that's marked ATTR_KILL_PRIV
 * affects the security markings on that inode, and if it is, should
 * inode_killpriv() be invoked or the change rejected?
 *
 * Returns 0 if granted; +ve if granted, but inode_killpriv() is required; and
 * -ve to deny the change.
 */
int cap_inode_need_killpriv(struct dentry *dentry)
{
        struct inode *inode = dentry->d_inode;
        int error;

        if (!inode->i_op->getxattr)
               return 0;

        error = inode->i_op->getxattr(dentry, XATTR_NAME_CAPS, NULL, 0);
        if (error <= 0)
                return 0;
        return 1;
}

/**
 * cap_inode_killpriv - Erase the security markings on an inode
 * @dentry: The inode/dentry to alter
 *
 * Erase the privilege-enhancing security markings on an inode.
 *
 * Returns 0 if successful, -ve on error.
 */
int cap_inode_killpriv(struct dentry *dentry)
{
        struct inode *inode = dentry->d_inode;

        if (!inode->i_op->removexattr)
               return 0;

        return inode->i_op->removexattr(dentry, XATTR_NAME_CAPS);
}

/*
 * Calculate the new process capability sets from the capability sets attached
 * to a file.
 */
static inline int bprm_caps_from_vfs_caps(struct cpu_vfs_cap_data *caps,
                                          struct linux_binprm *bprm,
                                          bool *effective)
{
        struct cred *new = bprm->cred;
        unsigned i;
        int ret = 0;

        if (caps->magic_etc & VFS_CAP_FLAGS_EFFECTIVE)
                *effective = true;

        CAP_FOR_EACH_U32(i) {
                __u32 permitted = caps->permitted.cap[i];
                __u32 inheritable = caps->inheritable.cap[i];

                /*
                 * pP' = (X & fP) | (pI & fI)
                 */
                new->cap_permitted.cap[i] =
                        (new->cap_bset.cap[i] & permitted) |
                        (new->cap_inheritable.cap[i] & inheritable);

                if (permitted & ~new->cap_permitted.cap[i])
                        /* insufficient to execute correctly */
                        ret = -EPERM;
        }

        /*
         * For legacy apps, with no internal support for recognizing they
         * do not have enough capabilities, we return an error if they are
         * missing some "forced" (aka file-permitted) capabilities.
         */
        return *effective ? ret : 0;
}

/*
 * Extract the on-exec-apply capability sets for an executable file.
 */
int get_vfs_caps_from_disk(const struct dentry *dentry, struct cpu_vfs_cap_data *cpu_caps)
{
        struct inode *inode = dentry->d_inode;
        __u32 magic_etc;
        unsigned tocopy, i;
        int size;
        struct vfs_cap_data caps;

        memset(cpu_caps, 0, sizeof(struct cpu_vfs_cap_data));

        if (!inode || !inode->i_op->getxattr)
                return -ENODATA;

        size = inode->i_op->getxattr((struct dentry *)dentry, XATTR_NAME_CAPS, &caps,
                                   XATTR_CAPS_SZ);
        if (size == -ENODATA || size == -EOPNOTSUPP)
                /* no data, that's ok */
                return -ENODATA;
        if (size < 0)
                return size;

        if (size < sizeof(magic_etc))
                return -EINVAL;

        cpu_caps->magic_etc = magic_etc = le32_to_cpu(caps.magic_etc);

        switch (magic_etc & VFS_CAP_REVISION_MASK) {
        case VFS_CAP_REVISION_1:
                if (size != XATTR_CAPS_SZ_1)
                        return -EINVAL;
                tocopy = VFS_CAP_U32_1;
                break;
        case VFS_CAP_REVISION_2:
                if (size != XATTR_CAPS_SZ_2)
                        return -EINVAL;
                tocopy = VFS_CAP_U32_2;
                break;
        default:
                return -EINVAL;
        }

        CAP_FOR_EACH_U32(i) {
                if (i >= tocopy)
                        break;
                cpu_caps->permitted.cap[i] = le32_to_cpu(caps.data[i].permitted);
                cpu_caps->inheritable.cap[i] = le32_to_cpu(caps.data[i].inheritable);
        }

        return 0;
}

/*
 * Attempt to get the on-exec apply capability sets for an executable file from
 * its xattrs and, if present, apply them to the proposed credentials being
 * constructed by execve().
 */
static int get_file_caps(struct linux_binprm *bprm, bool *effective)
{
        struct dentry *dentry;
        int rc = 0;
        struct cpu_vfs_cap_data vcaps;

        bprm_clear_caps(bprm);

        if (!file_caps_enabled)
                return 0;

        if (bprm->file->f_vfsmnt->mnt_flags & MNT_NOSUID)
                return 0;

        dentry = dget(bprm->file->f_dentry);

        rc = get_vfs_caps_from_disk(dentry, &vcaps);
        if (rc < 0) {
                if (rc == -EINVAL)
                        printk(KERN_NOTICE "%s: get_vfs_caps_from_disk returned %d for %s\n",
                                __func__, rc, bprm->filename);
                else if (rc == -ENODATA)
                        rc = 0;
                goto out;
        }

        rc = bprm_caps_from_vfs_caps(&vcaps, bprm, effective);
        if (rc == -EINVAL)
                printk(KERN_NOTICE "%s: cap_from_disk returned %d for %s\n",
                       __func__, rc, bprm->filename);

out:
        dput(dentry);
        if (rc)
                bprm_clear_caps(bprm);

        return rc;
}

/**
 * cap_bprm_set_creds - Set up the proposed credentials for execve().
 * @bprm: The execution parameters, including the proposed creds
 *
 * Set up the proposed credentials for a new execution context being
 * constructed by execve().  The proposed creds in @bprm->cred is altered,
 * which won't take effect immediately.  Returns 0 if successful, -ve on error.
 */
int cap_bprm_set_creds(struct linux_binprm *bprm)
{
        const struct cred *old = current_cred();
        struct cred *new = bprm->cred;
        bool effective;
        int ret;

        effective = false;
        ret = get_file_caps(bprm, &effective);
        if (ret < 0)
                return ret;

        if (!issecure(SECURE_NOROOT)) {
                /*
                 * If the legacy file capability is set, then don't set privs
                 * for a setuid root binary run by a non-root user.  Do set it
                 * for a root user just to cause least surprise to an admin.
                 */
                if (effective && new->uid != 0 && new->euid == 0) {
                        warn_setuid_and_fcaps_mixed(bprm->filename);
                        goto skip;
                }
                /*
                 * To support inheritance of root-permissions and suid-root
                 * executables under compatibility mode, we override the
                 * capability sets for the file.
                 *
                 * If only the real uid is 0, we do not set the effective bit.
                 */
                if (new->euid == 0 || new->uid == 0) {
                        /* pP' = (cap_bset & ~0) | (pI & ~0) */
                        new->cap_permitted = cap_combine(old->cap_bset,
                                                         old->cap_inheritable);
                }
                if (new->euid == 0)
                        effective = true;
        }
skip:

        /* Don't let someone trace a set[ug]id/setpcap binary with the revised
         * credentials unless they have the appropriate permit
         */
        if ((new->euid != old->uid ||
             new->egid != old->gid ||
             !cap_issubset(new->cap_permitted, old->cap_permitted)) &&
            bprm->unsafe & ~LSM_UNSAFE_PTRACE_CAP) {
                /* downgrade; they get no more than they had, and maybe less */
                if (!capable(CAP_SETUID)) {
                        new->euid = new->uid;
                        new->egid = new->gid;
                }
                new->cap_permitted = cap_intersect(new->cap_permitted,
                                                   old->cap_permitted);
        }

        new->suid = new->fsuid = new->euid;
        new->sgid = new->fsgid = new->egid;

        /* For init, we want to retain the capabilities set in the initial
         * task.  Thus we skip the usual capability rules
         */
        if (!is_global_init(current)) {
                if (effective)
                        new->cap_effective = new->cap_permitted;
                else
                        cap_clear(new->cap_effective);
        }
        bprm->cap_effective = effective;

        /*
         * Audit candidate if current->cap_effective is set
         *
         * We do not bother to audit if 3 things are true:
         *   1) cap_effective has all caps
         *   2) we are root
         *   3) root is supposed to have all caps (SECURE_NOROOT)
         * Since this is just a normal root execing a process.
         *
         * Number 1 above might fail if you don't have a full bset, but I think
         * that is interesting information to audit.
         */
        if (!cap_isclear(new->cap_effective)) {
                if (!cap_issubset(CAP_FULL_SET, new->cap_effective) ||
                    new->euid != 0 || new->uid != 0 ||
                    issecure(SECURE_NOROOT)) {
                        ret = audit_log_bprm_fcaps(bprm, new, old);
                        if (ret < 0)
                                return ret;
                }
        }

        new->securebits &= ~issecure_mask(SECURE_KEEP_CAPS);
        return 0;
}

/**
 * cap_bprm_secureexec - Determine whether a secure execution is required
 * @bprm: The execution parameters
 *
 * Determine whether a secure execution is required, return 1 if it is, and 0
 * if it is not.
 *
 * The credentials have been committed by this point, and so are no longer
 * available through @bprm->cred.
 */
int cap_bprm_secureexec(struct linux_binprm *bprm)
{
        const struct cred *cred = current_cred();

        if (cred->uid != 0) {
                if (bprm->cap_effective)
                        return 1;
                if (!cap_isclear(cred->cap_permitted))
                        return 1;
        }

        return (cred->euid != cred->uid ||
                cred->egid != cred->gid);
}

/**
 * cap_inode_setxattr - Determine whether an xattr may be altered
 * @dentry: The inode/dentry being altered
 * @name: The name of the xattr to be changed
 * @value: The value that the xattr will be changed to
 * @size: The size of value
 * @flags: The replacement flag
 *
 * Determine whether an xattr may be altered or set on an inode, returning 0 if
 * permission is granted, -ve if denied.
 *
 * This is used to make sure security xattrs don't get updated or set by those
 * who aren't privileged to do so.
 */
int cap_inode_setxattr(struct dentry *dentry, const char *name,
                       const void *value, size_t size, int flags)
{
        if (!strcmp(name, XATTR_NAME_CAPS)) {
                if (!capable(CAP_SETFCAP))
                        return -EPERM;
                return 0;
        }

        if (!strncmp(name, XATTR_SECURITY_PREFIX,
                     sizeof(XATTR_SECURITY_PREFIX) - 1) &&
            !capable(CAP_SYS_ADMIN))
                return -EPERM;
        return 0;
}

/**
 * cap_inode_removexattr - Determine whether an xattr may be removed
 * @dentry: The inode/dentry being altered
 * @name: The name of the xattr to be changed
 *
 * Determine whether an xattr may be removed from an inode, returning 0 if
 * permission is granted, -ve if denied.
 *
 * This is used to make sure security xattrs don't get removed by those who
 * aren't privileged to remove them.
 */
int cap_inode_removexattr(struct dentry *dentry, const char *name)
{
        if (!strcmp(name, XATTR_NAME_CAPS)) {
                if (!capable(CAP_SETFCAP))
                        return -EPERM;
                return 0;
        }

        if (!strncmp(name, XATTR_SECURITY_PREFIX,
                     sizeof(XATTR_SECURITY_PREFIX) - 1) &&
            !capable(CAP_SYS_ADMIN))
                return -EPERM;
        return 0;
}

/*
 * cap_emulate_setxuid() fixes the effective / permitted capabilities of
 * a process after a call to setuid, setreuid, or setresuid.
 *
 *  1) When set*uiding _from_ one of {r,e,s}uid == 0 _to_ all of
 *  {r,e,s}uid != 0, the permitted and effective capabilities are
 *  cleared.
 *
 *  2) When set*uiding _from_ euid == 0 _to_ euid != 0, the effective
 *  capabilities of the process are cleared.
 *
 *  3) When set*uiding _from_ euid != 0 _to_ euid == 0, the effective
 *  capabilities are set to the permitted capabilities.
 *
 *  fsuid is handled elsewhere. fsuid == 0 and {r,e,s}uid!= 0 should
 *  never happen.
 *
 *  -astor
 *
 * cevans - New behaviour, Oct '99
 * A process may, via prctl(), elect to keep its capabilities when it
 * calls setuid() and switches away from uid==0. Both permitted and
 * effective sets will be retained.
 * Without this change, it was impossible for a daemon to drop only some
 * of its privilege. The call to setuid(!=0) would drop all privileges!
 * Keeping uid 0 is not an option because uid 0 owns too many vital
 * files..
 * Thanks to Olaf Kirch and Peter Benie for spotting this.
 */
static inline void cap_emulate_setxuid(struct cred *new, const struct cred *old)
{
        if ((old->uid == 0 || old->euid == 0 || old->suid == 0) &&
            (new->uid != 0 && new->euid != 0 && new->suid != 0) &&
            !issecure(SECURE_KEEP_CAPS)) {
                cap_clear(new->cap_permitted);
                cap_clear(new->cap_effective);
        }
        if (old->euid == 0 && new->euid != 0)
                cap_clear(new->cap_effective);
        if (old->euid != 0 && new->euid == 0)
                new->cap_effective = new->cap_permitted;
}

/**
 * cap_task_fix_setuid - Fix up the results of setuid() call
 * @new: The proposed credentials
 * @old: The current task's current credentials
 * @flags: Indications of what has changed
 *
 * Fix up the results of setuid() call before the credential changes are
 * actually applied, returning 0 to grant the changes, -ve to deny them.
 */
int cap_task_fix_setuid(struct cred *new, const struct cred *old, int flags)
{
        switch (flags) {
        case LSM_SETID_RE:
        case LSM_SETID_ID:
        case LSM_SETID_RES:
                /* juggle the capabilities to follow [RES]UID changes unless
                 * otherwise suppressed */
                if (!issecure(SECURE_NO_SETUID_FIXUP))
                        cap_emulate_setxuid(new, old);
                break;

        case LSM_SETID_FS:
                /* juggle the capabilties to follow FSUID changes, unless
                 * otherwise suppressed
                 *
                 * FIXME - is fsuser used for all CAP_FS_MASK capabilities?
                 *          if not, we might be a bit too harsh here.
                 */
                if (!issecure(SECURE_NO_SETUID_FIXUP)) {
                        if (old->fsuid == 0 && new->fsuid != 0)
                                new->cap_effective =
                                        cap_drop_fs_set(new->cap_effective);

                        if (old->fsuid != 0 && new->fsuid == 0)
                                new->cap_effective =
                                        cap_raise_fs_set(new->cap_effective,
                                                         new->cap_permitted);
                }
                break;

        default:
                return -EINVAL;
        }

        return 0;
}

/*
 * Rationale: code calling task_setscheduler, task_setioprio, and
 * task_setnice, assumes that
 *   . if capable(cap_sys_nice), then those actions should be allowed
 *   . if not capable(cap_sys_nice), but acting on your own processes,
 *      then those actions should be allowed
 * This is insufficient now since you can call code without suid, but
 * yet with increased caps.
 * So we check for increased caps on the target process.
 */
static int cap_safe_nice(struct task_struct *p)
{
        int is_subset;

        rcu_read_lock();
        is_subset = cap_issubset(__task_cred(p)->cap_permitted,
                                 current_cred()->cap_permitted);
        rcu_read_unlock();

        if (!is_subset && !capable(CAP_SYS_NICE))
                return -EPERM;
        return 0;
}

/**
 * cap_task_setscheduler - Detemine if scheduler policy change is permitted
 * @p: The task to affect
 *
 * Detemine if the requested scheduler policy change is permitted for the
 * specified task, returning 0 if permission is granted, -ve if denied.
 */
int cap_task_setscheduler(struct task_struct *p)
{
        return cap_safe_nice(p);
}

/**
 * cap_task_ioprio - Detemine if I/O priority change is permitted
 * @p: The task to affect
 * @ioprio: The I/O priority to set
 *
 * Detemine if the requested I/O priority change is permitted for the specified
 * task, returning 0 if permission is granted, -ve if denied.
 */
int cap_task_setioprio(struct task_struct *p, int ioprio)
{
        return cap_safe_nice(p);
}

/**
 * cap_task_ioprio - Detemine if task priority change is permitted
 * @p: The task to affect
 * @nice: The nice value to set
 *
 * Detemine if the requested task priority change is permitted for the
 * specified task, returning 0 if permission is granted, -ve if denied.
 */
int cap_task_setnice(struct task_struct *p, int nice)
{
        return cap_safe_nice(p);
}

/*
 * Implement PR_CAPBSET_DROP.  Attempt to remove the specified capability from
 * the current task's bounding set.  Returns 0 on success, -ve on error.
 */
static long cap_prctl_drop(struct cred *new, unsigned long cap)
{
        if (!capable(CAP_SETPCAP))
                return -EPERM;
        if (!cap_valid(cap))
                return -EINVAL;

        cap_lower(new->cap_bset, cap);
        return 0;
}

/**
 * cap_task_prctl - Implement process control functions for this security module
 * @option: The process control function requested
 * @arg2, @arg3, @arg4, @arg5: The argument data for this function
 *
 * Allow process control functions (sys_prctl()) to alter capabilities; may
 * also deny access to other functions not otherwise implemented here.
 *
 * Returns 0 or +ve on success, -ENOSYS if this function is not implemented
 * here, other -ve on error.  If -ENOSYS is returned, sys_prctl() and other LSM
 * modules will consider performing the function.
 */
int cap_task_prctl(int option, unsigned long arg2, unsigned long arg3,
                   unsigned long arg4, unsigned long arg5)
{
        struct cred *new;
        long error = 0;

        new = prepare_creds();
        if (!new)
                return -ENOMEM;

        switch (option) {
        case PR_CAPBSET_READ:
                error = -EINVAL;
                if (!cap_valid(arg2))
                        goto error;
                error = !!cap_raised(new->cap_bset, arg2);
                goto no_change;

        case PR_CAPBSET_DROP:
                error = cap_prctl_drop(new, arg2);
                if (error < 0)
                        goto error;
                goto changed;

        /*
         * The next four prctl's remain to assist with transitioning a
         * system from legacy UID=0 based privilege (when filesystem
         * capabilities are not in use) to a system using filesystem
         * capabilities only - as the POSIX.1e draft intended.
         *
         * Note:
         *
         *  PR_SET_SECUREBITS =
         *      issecure_mask(SECURE_KEEP_CAPS_LOCKED)
         *    | issecure_mask(SECURE_NOROOT)
         *    | issecure_mask(SECURE_NOROOT_LOCKED)
         *    | issecure_mask(SECURE_NO_SETUID_FIXUP)
         *    | issecure_mask(SECURE_NO_SETUID_FIXUP_LOCKED)
         *
         * will ensure that the current process and all of its
         * children will be locked into a pure
         * capability-based-privilege environment.
         */
        case PR_SET_SECUREBITS:
                error = -EPERM;
                if ((((new->securebits & SECURE_ALL_LOCKS) >> 1)
                     & (new->securebits ^ arg2))                        /*[1]*/
                    || ((new->securebits & SECURE_ALL_LOCKS & ~arg2))   /*[2]*/
                    || (arg2 & ~(SECURE_ALL_LOCKS | SECURE_ALL_BITS))   /*[3]*/
                    || (cap_capable(current, current_cred(),
                                    current_cred()->user->user_ns, CAP_SETPCAP,
                                    SECURITY_CAP_AUDIT) != 0)           /*[4]*/
                        /*
                         * [1] no changing of bits that are locked
                         * [2] no unlocking of locks
                         * [3] no setting of unsupported bits
                         * [4] doing anything requires privilege (go read about
                         *     the "sendmail capabilities bug")
                         */
                    )
                        /* cannot change a locked bit */
                        goto error;
                new->securebits = arg2;
                goto changed;

        case PR_GET_SECUREBITS:
                error = new->securebits;
                goto no_change;

        case PR_GET_KEEPCAPS:
                if (issecure(SECURE_KEEP_CAPS))
                        error = 1;
                goto no_change;

        case PR_SET_KEEPCAPS:
                error = -EINVAL;
                if (arg2 > 1) /* Note, we rely on arg2 being unsigned here */
                        goto error;
                error = -EPERM;
                if (issecure(SECURE_KEEP_CAPS_LOCKED))
                        goto error;
                if (arg2)
                        new->securebits |= issecure_mask(SECURE_KEEP_CAPS);
                else
                        new->securebits &= ~issecure_mask(SECURE_KEEP_CAPS);
                goto changed;

        default:
                /* No functionality available - continue with default */
                error = -ENOSYS;
                goto error;
        }

        /* Functionality provided */
changed:
        return commit_creds(new);

no_change:
error:
        abort_creds(new);
        return error;
}

/**
 * cap_vm_enough_memory - Determine whether a new virtual mapping is permitted
 * @mm: The VM space in which the new mapping is to be made
 * @pages: The size of the mapping
 *
 * Determine whether the allocation of a new virtual mapping by the current
 * task is permitted, returning 0 if permission is granted, -ve if not.
 */
int cap_vm_enough_memory(struct mm_struct *mm, long pages)
{
        int cap_sys_admin = 0;

        if (cap_capable(current, current_cred(), &init_user_ns, CAP_SYS_ADMIN,
                        SECURITY_CAP_NOAUDIT) == 0)
                cap_sys_admin = 1;
        return __vm_enough_memory(mm, pages, cap_sys_admin);
}

/*
 * cap_file_mmap - check if able to map given addr
 * @file: unused
 * @reqprot: unused
 * @prot: unused
 * @flags: unused
 * @addr: address attempting to be mapped
 * @addr_only: unused
 *
 * If the process is attempting to map memory below dac_mmap_min_addr they need
 * CAP_SYS_RAWIO.  The other parameters to this function are unused by the
 * capability security module.  Returns 0 if this mapping should be allowed
 * -EPERM if not.
 */
int cap_file_mmap(struct file *file, unsigned long reqprot,
                  unsigned long prot, unsigned long flags,
                  unsigned long addr, unsigned long addr_only)
{
        int ret = 0;

        if (addr < dac_mmap_min_addr) {
                ret = cap_capable(current, current_cred(), &init_user_ns, CAP_SYS_RAWIO,
                                  SECURITY_CAP_AUDIT);
                /* set PF_SUPERPRIV if it turns out we allow the low mmap */
                if (ret == 0)
                        current->flags |= PF_SUPERPRIV;
        }
        return ret;
}