source: azure_iot_hub/trunk/musl-1.1.18/src/passwd/getspnam_r.c@ 388

#include <fcntl.h>
#include <unistd.h>
#include <sys/stat.h>
#include <ctype.h>
#include <pthread.h>
#include "pwf.h"

/* This implementation support Openwall-style TCB passwords in place of
 * traditional shadow, if the appropriate directories and files exist.
 * Thus, it is careful to avoid following symlinks or blocking on fifos
 * which a malicious user might create in place of his or her TCB shadow
 * file. It also avoids any allocation to prevent memory-exhaustion
 * attacks via huge TCB shadow files. */

static long xatol(char **s)
{
        long x;
        if (**s == ':' || **s == '\n') return -1;
        for (x=0; **s-'0'<10U; ++*s) x=10*x+(**s-'0');
        return x;
}

int __parsespent(char *s, struct spwd *sp)
{
        sp->sp_namp = s;
        if (!(s = strchr(s, ':'))) return -1;
        *s = 0;

        sp->sp_pwdp = ++s;
        if (!(s = strchr(s, ':'))) return -1;
        *s = 0;

        s++; sp->sp_lstchg = xatol(&s);
        if (*s != ':') return -1;

        s++; sp->sp_min = xatol(&s);
        if (*s != ':') return -1;

        s++; sp->sp_max = xatol(&s);
        if (*s != ':') return -1;

        s++; sp->sp_warn = xatol(&s);
        if (*s != ':') return -1;

        s++; sp->sp_inact = xatol(&s);
        if (*s != ':') return -1;

        s++; sp->sp_expire = xatol(&s);
        if (*s != ':') return -1;

        s++; sp->sp_flag = xatol(&s);
        if (*s != '\n') return -1;
        return 0;
}

static void cleanup(void *p)
{
        fclose(p);
}

int getspnam_r(const char *name, struct spwd *sp, char *buf, size_t size, struct spwd **res)
{
        char path[20+NAME_MAX];
        FILE *f = 0;
        int rv = 0;
        int fd;
        size_t k, l = strlen(name);
        int skip = 0;
        int cs;

        *res = 0;

        /* Disallow potentially-malicious user names */
        if (*name=='.' || strchr(name, '/') || !l)
                return errno = EINVAL;

        /* Buffer size must at least be able to hold name, plus some.. */
        if (size < l+100)
                return errno = ERANGE;

        /* Protect against truncation */
        if (snprintf(path, sizeof path, "/etc/tcb/%s/shadow", name) >= sizeof path)
                return errno = EINVAL;

        fd = open(path, O_RDONLY|O_NOFOLLOW|O_NONBLOCK|O_CLOEXEC);
        if (fd >= 0) {
                struct stat st = { 0 };
                errno = EINVAL;
                if (fstat(fd, &st) || !S_ISREG(st.st_mode) || !(f = fdopen(fd, "rb"))) {
                        pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &cs);
                        close(fd);
                        pthread_setcancelstate(cs, 0);
                        return errno;
                }
        } else {
                f = fopen("/etc/shadow", "rbe");
                if (!f) return errno;
        }

        pthread_cleanup_push(cleanup, f);
        while (fgets(buf, size, f) && (k=strlen(buf))>0) {
                if (skip || strncmp(name, buf, l) || buf[l]!=':') {
                        skip = buf[k-1] != '\n';
                        continue;
                }
                if (buf[k-1] != '\n') {
                        rv = ERANGE;
                        break;
                }

                if (__parsespent(buf, sp) < 0) continue;
                *res = sp;
                break;
        }
        pthread_cleanup_pop(1);
        if (rv) errno = rv;
        return rv;
}