openssh unix dev - Jul 2014 - openssh portable and libressl portable cause recursion between arc4random and RAND_bytes

Hi,

Yesterday I tried to replace the system openssl in a gentoo system with
libressl.

With openssh an interesting issue popped up:
* RAND_bytes in libressl calls arc4random
* arc4random is a compat function both in openssh and libressl
* arc4random from openssh uses RAND_bytes

So what's happening is a recursion. arc4random wants to use RAND_bytes
and RAND_bytes wants to use arc4random. The result is a segfault.
OpenSSH is the latest 6.6.1.

A quick and working solution was to replace the openssh-arc4random with
the one shipped by libressl. One small change is needed: the
libressl-arc4random.c doesn't have the arc4random_stir()-function,
I copied that back from the openssh-arc4random.c.

Works so far, see attached patch.

An alternative would be to check for the availability of arc4random in
libcrypto and use that if available.

cu,
-- 
Hanno B?ck
http://hboeck.de/

mail/jabber: hanno at hboeck.de
GPG: BBB51E42
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On Sat, 12 Jul 2014, Hanno B?ck wrote:
> Hi,
> 
> Yesterday I tried to replace the system openssl in a gentoo system with
> libressl.
> 
> With openssh an interesting issue popped up:
> * RAND_bytes in libressl calls arc4random
> * arc4random is a compat function both in openssh and libressl
> * arc4random from openssh uses RAND_bytes
Right, I think we should just delay the checks for arc4random. I'd like
to sync arc4random.c, but that's a separate issue.

Can you tell me if this works for you?

Index: configure.ac
==================================================================RCS file:
/var/cvs/openssh/configure.ac,v
retrieving revision 1.577
diff -u -p -r1.577 configure.ac
--- configure.ac	3 Jul 2014 01:54:19 -0000	1.577
+++ configure.ac	13 Jul 2014 23:34:33 -0000
@@ -1575,10 +1575,6 @@ AC_CHECK_FUNCS([ \
 	Blowfish_expandstate \
 	Blowfish_expand0state \
 	Blowfish_stream2word \
-	arc4random \
-	arc4random_buf \
-	arc4random_stir \
-	arc4random_uniform \
 	asprintf \
 	b64_ntop \
 	__b64_ntop \
@@ -2639,6 +2635,13 @@ fi
 
 AC_SUBST([TEST_SSH_ECC])
 AC_SUBST([COMMENT_OUT_ECC])
+
+AC_CHECK_FUNCS([ \
+	arc4random \
+	arc4random_buf \
+	arc4random_stir \
+	arc4random_uniform \
+])
 
 saved_LIBS="$LIBS"
 AC_CHECK_LIB([iaf], [ia_openinfo], [