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Manual Reference Pages  - GETGROUPLIST (2)

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getgrouplist - list of groups a user belongs to

CONTENTS

Synopsis
Description
Bugs
Example

#include <grp.h>

int getgrouplist (const char *user, gid_t group, gid_t *groups, int *ngroups);

The getgrouplist() function scans the group database for all the groups user belongs to. Up to *ngroups group IDs corresponding to these groups are stored in the array groups; the return value from the function is the number of group IDs actually stored. The group group is automatically included in the list of groups returned by getgroup list().

If *ngroups is smaller than the total number of groups found, then getgrouplist() returns a value of ‘-1’. In all cases the actual number of groups is stored in *ngroups.

The glibc 2.3.2 implementation of this function is broken: it overwrites memory when the actual number of groups is larger than *ngroups.

This function is present since glibc 2.2.4.

/* This crashes with glibc 2.3.2 */
#include <stdio.h>
#include <stdlib.h>
#include <grp.h>
#include <pwd.h>

int main() {
        int i, ng = 0;
        char *user = "who";     /* username here */
        gid_t *groups = NULL;
        struct passwd *pw = getpwnam(user);
        if (pw == NULL)
                return 0;

        if (getgrouplist(user, pw->pw_gid, NULL, &ng) < 0) {
                groups = (gid_t *) malloc(ng * sizeof (gid_t));
                getgrouplist(user, pw->pw_gid, groups, &ng);
        }

        for(i = 0; i < ng; i++)
                printf("%d\n", groups[i]);

        return 0;
}

getgroups(3), setgroups(3)

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