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

fusl/src/passwd/getspnam_r.c

+#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 EINVAL;
+
+        /* Buffer size must at least be able to hold name, plus some.. */
+        if (size < l+100) return ERANGE;
+
+        /* Protect against truncation */
+        if (snprintf(path, sizeof path, "/etc/tcb/%s/shadow", name) >= sizeof path)
+                return 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);
+        return rv;
+}