source: azure_iot_hub/trunk/musl-1.1.18/src/passwd/getpw_a.c@ 389

#include <pthread.h>
#include <byteswap.h>
#include <string.h>
#include <unistd.h>
#include "pwf.h"
#include "nscd.h"

static char *itoa(char *p, uint32_t x)
{
        // number of digits in a uint32_t + NUL
        p += 11;
        *--p = 0;
        do {
                *--p = '0' + x % 10;
                x /= 10;
        } while (x);
        return p;
}

int __getpw_a(const char *name, uid_t uid, struct passwd *pw, char **buf, size_t *size, struct passwd **res)
{
        FILE *f;
        int cs;
        int rv = 0;

        *res = 0;

        pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &cs);

        f = fopen("/etc/passwd", "rbe");
        if (!f) {
                rv = errno;
                goto done;
        }

        while (!(rv = __getpwent_a(f, pw, buf, size, res)) && *res) {
                if (name && !strcmp(name, (*res)->pw_name)
                || !name && (*res)->pw_uid == uid)
                        break;
        }
        fclose(f);

        if (!*res && (rv == 0 || rv == ENOENT || rv == ENOTDIR)) {
                int32_t req = name ? GETPWBYNAME : GETPWBYUID;
                const char *key;
                int32_t passwdbuf[PW_LEN] = {0};
                size_t len = 0;
                char uidbuf[11] = {0};

                if (name) {
                        key = name;
                } else {
                        /* uid outside of this range can't be queried with the
                         * nscd interface, but might happen if uid_t ever
                         * happens to be a larger type (this is not true as of
                         * now)
                         */
                        if(uid < 0 || uid > UINT32_MAX) {
                                rv = 0;
                                goto done;
                        }
                        key = itoa(uidbuf, uid);
                }

                f = __nscd_query(req, key, passwdbuf, sizeof passwdbuf, (int[]){0});
                if (!f) { rv = errno; goto done; }

                if(!passwdbuf[PWFOUND]) { rv = 0; goto cleanup_f; }

                /* A zero length response from nscd is invalid. We ignore
                 * invalid responses and just report an error, rather than
                 * trying to do something with them.
                 */
                if (!passwdbuf[PWNAMELEN] || !passwdbuf[PWPASSWDLEN]
                || !passwdbuf[PWGECOSLEN] || !passwdbuf[PWDIRLEN]
                || !passwdbuf[PWSHELLLEN]) {
                        rv = EIO;
                        goto cleanup_f;
                }

                if ((passwdbuf[PWNAMELEN]|passwdbuf[PWPASSWDLEN]
                     |passwdbuf[PWGECOSLEN]|passwdbuf[PWDIRLEN]
                     |passwdbuf[PWSHELLLEN]) >= SIZE_MAX/8) {
                        rv = ENOMEM;
                        goto cleanup_f;
                }

                len = passwdbuf[PWNAMELEN] + passwdbuf[PWPASSWDLEN]
                    + passwdbuf[PWGECOSLEN] + passwdbuf[PWDIRLEN]
                    + passwdbuf[PWSHELLLEN];

                if (len > *size || !*buf) {
                        char *tmp = realloc(*buf, len);
                        if (!tmp) {
                                rv = errno;
                                goto cleanup_f;
                        }
                        *buf = tmp;
                        *size = len;
                }

                if (!fread(*buf, len, 1, f)) {
                        rv = ferror(f) ? errno : EIO;
                        goto cleanup_f;
                }

                pw->pw_name = *buf;
                pw->pw_passwd = pw->pw_name + passwdbuf[PWNAMELEN];
                pw->pw_gecos = pw->pw_passwd + passwdbuf[PWPASSWDLEN];
                pw->pw_dir = pw->pw_gecos + passwdbuf[PWGECOSLEN];
                pw->pw_shell = pw->pw_dir + passwdbuf[PWDIRLEN];
                pw->pw_uid = passwdbuf[PWUID];
                pw->pw_gid = passwdbuf[PWGID];

                /* Don't assume that nscd made sure to null terminate strings.
                 * It's supposed to, but malicious nscd should be ignored
                 * rather than causing a crash.
                 */
                if (pw->pw_passwd[-1] || pw->pw_gecos[-1] || pw->pw_dir[-1]
                || pw->pw_shell[passwdbuf[PWSHELLLEN]-1]) {
                        rv = EIO;
                        goto cleanup_f;
                }

                if (name && strcmp(name, pw->pw_name)
                || !name && uid != pw->pw_uid) {
                        rv = EIO;
                        goto cleanup_f;
                }


                *res = pw;
cleanup_f:
                fclose(f);
                goto done;
        }

done:
        pthread_setcancelstate(cs, 0);
        if (rv) errno = rv;
        return rv;
}