Module Name: src
Committed By: riastradh
Date: Wed May 24 20:22:23 UTC 2023
Modified Files:
src/sys/kern: kern_entropy.c
Log Message:
entropy(9): Avoid race between rnd_add_data and ioctl(RNDCTL).
XXX pullup-10
To generate a diff of this commit:
cvs rdiff -u -r1.60 -r1.61 src/sys/kern/kern_entropy.c
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/sys/kern/kern_entropy.c
diff -u src/sys/kern/kern_entropy.c:1.60 src/sys/kern/kern_entropy.c:1.61
--- src/sys/kern/kern_entropy.c:1.60 Wed May 24 20:22:12 2023
+++ src/sys/kern/kern_entropy.c Wed May 24 20:22:23 2023
@@ -1,4 +1,4 @@
-/* $NetBSD: kern_entropy.c,v 1.60 2023/05/24 20:22:12 riastradh Exp $ */
+/* $NetBSD: kern_entropy.c,v 1.61 2023/05/24 20:22:23 riastradh Exp $ */
/*-
* Copyright (c) 2019 The NetBSD Foundation, Inc.
@@ -75,7 +75,7 @@
*/
#include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: kern_entropy.c,v 1.60 2023/05/24 20:22:12 riastradh Exp $");
+__KERNEL_RCSID(0, "$NetBSD: kern_entropy.c,v 1.61 2023/05/24 20:22:23 riastradh Exp $");
#include <sys/param.h>
#include <sys/types.h>
@@ -1910,6 +1910,14 @@ rnd_add_data(struct krndsource *rs, cons
return;
}
+ /*
+ * Hold up the reset xcall before it zeroes the entropy counts
+ * on this CPU or globally. Otherwise, we might leave some
+ * nonzero entropy attributed to an untrusted source in the
+ * event of a race with a change to flags.
+ */
+ kpreempt_disable();
+
/* Load a snapshot of the flags. Ioctl may change them under us. */
flags = atomic_load_relaxed(&rs->flags);
@@ -1922,7 +1930,7 @@ rnd_add_data(struct krndsource *rs, cons
if (!atomic_load_relaxed(&entropy_collection) ||
ISSET(flags, RND_FLAG_NO_COLLECT) ||
!ISSET(flags, RND_FLAG_COLLECT_VALUE|RND_FLAG_COLLECT_TIME))
- return;
+ goto out;
/* If asked, ignore the estimate. */
if (ISSET(flags, RND_FLAG_NO_ESTIMATE))
@@ -1939,6 +1947,9 @@ rnd_add_data(struct krndsource *rs, cons
rnd_add_data_1(rs, &extra, sizeof extra, 0,
RND_FLAG_COLLECT_TIME);
}
+
+out: /* Allow concurrent changes to flags to finish. */
+ kpreempt_enable();
}
static unsigned
