/*
 * Supplementary group IDs
 */
#include <linux/cred.h>
#include <linux/export.h>
#include <linux/slab.h>
#include <linux/security.h>
#include <linux/syscalls.h>
#include <linux/user_namespace.h>
#include <asm/uaccess.h>

/* init to 2 - one for init_task, one to ensure it is never freed */
struct group_info init_groups = { .usage = ATOMIC_INIT(2) };

struct group_info *groups_alloc(int gidsetsize)
{
        struct group_info *group_info;
        int nblocks;
        int i;

        nblocks = (gidsetsize + NGROUPS_PER_BLOCK - 1) / NGROUPS_PER_BLOCK;
        /* Make sure we always allocate at least one indirect block pointer */
        nblocks = nblocks ? : 1;
        group_info = kmalloc(sizeof(*group_info) + nblocks*sizeof(gid_t *), GFP_USER);
        if (!group_info)
                return NULL;
        group_info->ngroups = gidsetsize;
        group_info->nblocks = nblocks;
        atomic_set(&group_info->usage, 1);

        if (gidsetsize <= NGROUPS_SMALL)
                group_info->blocks[0] = group_info->small_block;
        else {
                for (i = 0; i < nblocks; i++) {
                        kgid_t *b;
                        b = (void *)__get_free_page(GFP_USER);
                        if (!b)
                                goto out_undo_partial_alloc;
                        group_info->blocks[i] = b;
                }
        }
        return group_info;

out_undo_partial_alloc:
        while (--i >= 0) {
                free_page((unsigned long)group_info->blocks[i]);
        }
        kfree(group_info);
        return NULL;
}

EXPORT_SYMBOL(groups_alloc);

void groups_free(struct group_info *group_info)
{
        if (group_info->blocks[0] != group_info->small_block) {
                int i;
                for (i = 0; i < group_info->nblocks; i++)
                        free_page((unsigned long)group_info->blocks[i]);
        }
        kfree(group_info);
}

EXPORT_SYMBOL(groups_free);

/* export the group_info to a user-space array */
static int groups_to_user(gid_t __user *grouplist,
                          const struct group_info *group_info)
{
        struct user_namespace *user_ns = current_user_ns();
        int i;
        unsigned int count = group_info->ngroups;

        for (i = 0; i < count; i++) {
                gid_t gid;
                gid = from_kgid_munged(user_ns, GROUP_AT(group_info, i));
                if (put_user(gid, grouplist+i))
                        return -EFAULT;
        }
        return 0;
}

/* fill a group_info from a user-space array - it must be allocated already */
static int groups_from_user(struct group_info *group_info,
    gid_t __user *grouplist)
{
        struct user_namespace *user_ns = current_user_ns();
        int i;
        unsigned int count = group_info->ngroups;

        for (i = 0; i < count; i++) {
                gid_t gid;
                kgid_t kgid;
                if (get_user(gid, grouplist+i))
                        return -EFAULT;

                kgid = make_kgid(user_ns, gid);
                if (!gid_valid(kgid))
                        return -EINVAL;

                GROUP_AT(group_info, i) = kgid;
        }
        return 0;
}

/* a simple Shell sort */
void groups_sort(struct group_info *group_info)
{
        /** Hello, dear friend,
         *  It seems that you are attempting to change groups_sort. If not, you
         *  can ignore this message.
         *
         *  There's a bug in 3.10 series in which two nfsd threads may race
         *  and cause corruptions in auth.unix.gid (RHBZ#1516978). Upstream, it
         *  was fixed by moving groups_sort outside set_groups. In RHEL7, the
         *  backport is partial, not removing the call to groups_sort from
         *  set_groups in order to prevent behavior changes. This is possible
         *  because shellsort is a NOP in case the groups are already ordered.
         *
         *  When changing set_groups, you need to make sure that either
         *  groups_sort is still a NOP or that you can safely remove the call
         *  to groups_sort from set_groups. Tests can be found in the bugzilla.
         */
        int base, max, stride;
        int gidsetsize = group_info->ngroups;

        for (stride = 1; stride < gidsetsize; stride = 3 * stride + 1)
                ; /* nothing */
        stride /= 3;

        while (stride) {
                max = gidsetsize - stride;
                for (base = 0; base < max; base++) {
                        int left = base;
                        int right = left + stride;
                        kgid_t tmp = GROUP_AT(group_info, right);

                        while (left >= 0 && gid_gt(GROUP_AT(group_info, left), tmp)) {
                                GROUP_AT(group_info, right) =
                                    GROUP_AT(group_info, left);
                                right = left;
                                left -= stride;
                        }
                        GROUP_AT(group_info, right) = tmp;
                }
                stride /= 3;
        }
}
EXPORT_SYMBOL(groups_sort);

/* a simple bsearch */
int groups_search(const struct group_info *group_info, kgid_t grp)
{
        unsigned int left, right;

        if (!group_info)
                return 0;

        left = 0;
        right = group_info->ngroups;
        while (left < right) {
                unsigned int mid = (left+right)/2;
                if (gid_gt(grp, GROUP_AT(group_info, mid)))
                        left = mid + 1;
                else if (gid_lt(grp, GROUP_AT(group_info, mid)))
                        right = mid;
                else
                        return 1;
        }
        return 0;
}

/**
 * set_groups - Change a group subscription in a set of credentials
 * @new: The newly prepared set of credentials to alter
 * @group_info: The group list to install
 *
 * Validate a group subscription and, if valid, insert it into a set
 * of credentials.
 */
int set_groups(struct cred *new, struct group_info *group_info)
{
        put_group_info(new->group_info);
        groups_sort(group_info);
        get_group_info(group_info);
        new->group_info = group_info;
        return 0;
}

EXPORT_SYMBOL(set_groups);

/**
 * set_current_groups - Change current's group subscription
 * @group_info: The group list to impose
 *
 * Validate a group subscription and, if valid, impose it upon current's task
 * security record.
 */
int set_current_groups(struct group_info *group_info)
{
        struct cred *new;
        int ret;

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

        ret = set_groups(new, group_info);
        if (ret < 0) {
                abort_creds(new);
                return ret;
        }

        return commit_creds(new);
}

EXPORT_SYMBOL(set_current_groups);

SYSCALL_DEFINE2(getgroups, int, gidsetsize, gid_t __user *, grouplist)
{
        const struct cred *cred = current_cred();
        int i;

        if (gidsetsize < 0)
                return -EINVAL;

        /* no need to grab task_lock here; it cannot change */
        i = cred->group_info->ngroups;
        if (gidsetsize) {
                if (i > gidsetsize) {
                        i = -EINVAL;
                        goto out;
                }
                if (groups_to_user(grouplist, cred->group_info)) {
                        i = -EFAULT;
                        goto out;
                }
        }
out:
        return i;
}

bool may_setgroups(void)
{
        struct user_namespace *user_ns = current_user_ns();

        return ns_capable(user_ns, CAP_SETGID) &&
                userns_may_setgroups(user_ns);
}

/*
 *      SMP: Our groups are copy-on-write. We can set them safely
 *      without another task interfering.
 */

SYSCALL_DEFINE2(setgroups, int, gidsetsize, gid_t __user *, grouplist)
{
        struct group_info *group_info;
        int retval;

        if (!may_setgroups())
                return -EPERM;
        if ((unsigned)gidsetsize > NGROUPS_MAX)
                return -EINVAL;

        group_info = groups_alloc(gidsetsize);
        if (!group_info)
                return -ENOMEM;
        retval = groups_from_user(group_info, grouplist);
        if (retval) {
                put_group_info(group_info);
                return retval;
        }

        groups_sort(group_info);
        retval = set_current_groups(group_info);
        put_group_info(group_info);

        return retval;
}

/*
 * Check whether we're fsgid/egid or in the supplemental group..
 */
int in_group_p(kgid_t grp)
{
        const struct cred *cred = current_cred();
        int retval = 1;

        if (!gid_eq(grp, cred->fsgid))
                retval = groups_search(cred->group_info, grp);
        return retval;
}

EXPORT_SYMBOL(in_group_p);

int in_egroup_p(kgid_t grp)
{
        const struct cred *cred = current_cred();
        int retval = 1;

        if (!gid_eq(grp, cred->egid))
                retval = groups_search(cred->group_info, grp);
        return retval;
}

EXPORT_SYMBOL(in_egroup_p);