lseek/read is racy when there is multiple consumers. Use pread instead.

Solves the startup issues seen by bluhm@. pread idea from guenther@.
While there save the errno in the error case.
OK bluhm@

diff --git a/usr.sbin/relayd/relay.c b/usr.sbin/relayd/relay.c
index a82f727..3361cdc 100644 (file)
--- a/usr.sbin/relayd/relay.c
+++ b/usr.sbin/relayd/relay.c
@@ -1,4 +1,4 @@
-/*     $OpenBSD: relay.c,v 1.231 2017/11/27 21:09:55 claudio Exp $     */
+/*     $OpenBSD: relay.c,v 1.232 2017/11/27 23:04:26 claudio Exp $     */
 
 /*
  * Copyright (c) 2006 - 2014 Reyk Floeter <reyk@openbsd.org>
@@ -2580,15 +2580,14 @@ relay_load_fd(int fd, off_t *len)
        struct stat      st;
        off_t            size;
        ssize_t          rv;
+       int              err;
 
        if (fstat(fd, &st) != 0)
                goto fail;
        size = st.st_size;
        if ((buf = calloc(1, size + 1)) == NULL)
                goto fail;
-       if (lseek(fd, 0, SEEK_SET) != 0)
-               goto fail;
-       if ((rv = read(fd, buf, size)) != size)
+       if ((rv = pread(fd, buf, size, 0)) != size)
                goto fail;
 
        close(fd);
@@ -2597,8 +2596,10 @@ relay_load_fd(int fd, off_t *len)
        return (buf);
 
  fail:
+       err = errno;
        free(buf);
        close(fd);
+       errno = err;
        return (NULL);
 }