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entropy(9): Avoid race between rnd_add_data and ioctl(RNDCTL). 

XXX pullup-10
This commit is contained in:
riastradh 2023-05-24 20:22:23 +00:00
parent b8bfbde6e8
commit 28811d5ecf
1 changed files with 14 additions and 3 deletions
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17
sys/kern/kern_entropy.c
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@ -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, const void *buf, uint32_t len,
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, const void *buf, uint32_t len,
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, const void *buf, uint32_t len,
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