kernel.txt

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++) {
			gid_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)

{

	int i;

	unsigned int count = group_info->ngroups;



	for (i = 0; i < group_info->nblocks; i++) {

		unsigned int cp_count = min(NGROUPS_PER_BLOCK, count);

		unsigned int len = cp_count * sizeof(*grouplist);



		if (copy_to_user(grouplist, group_info->blocks[i], len))

			return -EFAULT;



		grouplist += NGROUPS_PER_BLOCK;

		count -= cp_count;

	}

	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)

{

	int i;

	unsigned int count = group_info->ngroups;



	for (i = 0; i < group_info->nblocks; i++) {

		unsigned int cp_count = min(NGROUPS_PER_BLOCK, count);

		unsigned int len = cp_count * sizeof(*grouplist);



		if (copy_from_user(group_info->blocks[i], grouplist, len))

			return -EFAULT;



		grouplist += NGROUPS_PER_BLOCK;

		count -= cp_count;

	}

	return 0;

}



/* a simple Shell sort */

static void groups_sort(struct group_info *group_info)

{

	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;

			gid_t tmp = GROUP_AT(group_info, right);



			while (left >= 0 && 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;

	}

}



/* a simple bsearch */

int groups_search(const struct group_info *group_info, gid_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 - left)/2;

		if (grp > GROUP_AT(group_info, mid))

			left = mid + 1;

		else if (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;

}



/*

 *	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 (!nsown_capable(CAP_SETGID))

		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;

	}



	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(gid_t grp)

{

	const struct cred *cred = current_cred();

	int retval = 1;



	if (grp != cred->fsgid)

		retval = groups_search(cred->group_info, grp);

	return retval;

}



EXPORT_SYMBOL(in_group_p);



int in_egroup_p(gid_t grp)

{

	const struct cred *cred = current_cred();

	int retval = 1;



	if (grp != cred->egid)

		retval = groups_search(cred->group_info, grp);

	return retval;

}