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#include <errno.h> // for ERANGE, errno
#include <grp.h> // for group, getgrgid_r
#include <limits.h> // for LINE_MAX
#include <stdio.h> // for NULL, fclose, fgets, fopen, FILE
#include <stdlib.h> // for strtoul
#include <string.h> // for strtok, memcpy, strlen
#include <sys/types.h> // for gid_t, size_t
int getgrgid_r(gid_t gid, struct group *grp, char *buf, size_t buflen,
struct group **result)
{
FILE *f = fopen("/etc/group", "r");
if (!f) {
*result = NULL;
return errno;
}
char line[LINE_MAX];
char *members[1024];
while (fgets(line, sizeof(line), f)) {
char *name = strtok(line, ":");
char *passwd = strtok(NULL, ":");
char *gid_str = strtok(NULL, ":");
char *mem_str = strtok(NULL, "\n");
if (!name || !passwd || !gid_str)
continue;
gid_t file_gid = (gid_t)strtoul(gid_str, NULL, 10);
if (file_gid != gid)
continue;
size_t len = strlen(name) + 1;
if (len > buflen) {
fclose(f);
*result = NULL;
return ERANGE;
}
memcpy(buf, name, len);
grp->gr_name = buf;
buf += len;
buflen -= len;
grp->gr_gid = file_gid;
int i = 0;
if (mem_str && *mem_str) {
char *tok = strtok(mem_str, ",");
while (tok && i < 1023) {
size_t l = strlen(tok) + 1;
if (l > buflen) {
fclose(f);
*result = NULL;
return ERANGE;
}
memcpy(buf, tok, l);
members[i++] = buf;
buf += l;
buflen -= l;
tok = strtok(NULL, ",");
}
}
members[i] = NULL;
grp->gr_mem = members;
fclose(f);
*result = grp;
return 0;
}
fclose(f);
*result = NULL;
return 0;
}
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