Module Name: src
Committed By: riastradh
Date: Sun Jul 21 22:30:19 UTC 2013
Modified Files:
src/sys/dev: rndpseudo.c
Log Message:
When reading from /dev/random, block at most once in cprng_strong.
We are not obligated to return exactly as many bytes as requested,
and many applications -- notably those that use stdio or otherwise
buffered I/O to read from /dev/random -- try to read many more than
32 bytes at a time from /dev/random even if all they are about to use
is 32 bytes.
In this case, blocking until we have enough entropy to fill a large
buffer causes needless application delays, e.g. causing cgdconfig
(which reads from /dev/random with stdio) to hang at boot when trying
to configure a random-keyed device for swap.
Patch tested by Aran Clauson. Fixes PR kern/48028.
To generate a diff of this commit:
cvs rdiff -u -r1.15 -r1.16 src/sys/dev/rndpseudo.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/dev/rndpseudo.c
diff -u src/sys/dev/rndpseudo.c:1.15 src/sys/dev/rndpseudo.c:1.16
--- src/sys/dev/rndpseudo.c:1.15 Tue Jul 2 13:27:42 2013
+++ src/sys/dev/rndpseudo.c Sun Jul 21 22:30:19 2013
@@ -1,4 +1,4 @@
-/* $NetBSD: rndpseudo.c,v 1.15 2013/07/02 13:27:42 pgoyette Exp $ */
+/* $NetBSD: rndpseudo.c,v 1.16 2013/07/21 22:30:19 riastradh Exp $ */
/*-
* Copyright (c) 1997-2013 The NetBSD Foundation, Inc.
@@ -31,7 +31,7 @@
*/
#include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: rndpseudo.c,v 1.15 2013/07/02 13:27:42 pgoyette Exp $");
+__KERNEL_RCSID(0, "$NetBSD: rndpseudo.c,v 1.16 2013/07/21 22:30:19 riastradh Exp $");
#if defined(_KERNEL_OPT)
#include "opt_compat_netbsd.h"
@@ -387,6 +387,22 @@ rnd_read(struct file *fp, off_t *offp, s
error = uiomove(buf, n_read, uio);
if (error)
goto out;
+
+ /*
+ * Do at most one iteration for /dev/random and return
+ * a short read without hanging further. Hanging
+ * breaks applications worse than short reads. Reads
+ * can't be zero unless nonblocking from /dev/random;
+ * in that case, ask caller to retry, instead of just
+ * returning zero bytes, which means EOF.
+ */
+ KASSERT((0 < n_read) || (ctx->rc_hard &&
+ ISSET(fp->f_flag, FNONBLOCK)));
+ if (ctx->rc_hard) {
+ if (n_read == 0)
+ error = EAGAIN;
+ goto out;
+ }
}
out: pool_cache_put(rnd_temp_buffer_cache, buf);
