In dequeue_randomness() use an atomic instruction to increase the

rnd_event_cons. This way even concurrent calls to dequeue_randomness()
will use some different events.
OK deraadt@ djm@

diff --git a/sys/dev/rnd.c b/sys/dev/rnd.c
index 9bce17c..483ee30 100644 (file)
--- a/sys/dev/rnd.c
+++ b/sys/dev/rnd.c
@@ -1,4 +1,4 @@
-/*     $OpenBSD: rnd.c,v 1.226 2023/03/08 04:43:08 guenther Exp $      */
+/*     $OpenBSD: rnd.c,v 1.227 2024/06/04 08:26:11 claudio Exp $       */
 
 /*
  * Copyright (c) 2011,2020 Theo de Raadt.
@@ -261,7 +261,7 @@ dequeue_randomness(void *v)
                add_entropy_words(buf, 2);
        }
        /* and some probably more damaged */
-       startc = rnd_event_cons;
+       startc = atomic_add_int_nv(&rnd_event_cons, QEVCONSUME) - QEVCONSUME;
        for (i = 0; i < QEVCONSUME; i++) {
                u_int e = (startc + i) & (QEVLEN-1);
 
@@ -269,7 +269,6 @@ dequeue_randomness(void *v)
                buf[1] = rnd_event_space[e].re_val;
                add_entropy_words(buf, 2);
        }
-       rnd_event_cons = startp + QEVCONSUME;
 }
 
 /*