Add a "fork" of musl as //fusl.

fusl/src/passwd/getpw_a.c

+#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;
+}