openvpn: backport an upstream fix for a regression in using --cipher none (fixes #18676)

Signed-off-by: Felix Fietkau <nbd@openwrt.org>

Backport of r43823

git-svn-id: svn://svn.openwrt.org/openwrt/branches/barrier_breaker@43824 3c298f89-4303-0410-b956-a3cf2f4a3e73

package/network/services/openvpn/patches/001-backport_cipher_none_fix.patch

@@ -0,0 +1,57 @@
+commit 98156e90e1e83133a6a6a020db8e7333ada6156b
+Author: Steffan Karger <steffan@karger.me>
+Date:   Tue Dec 2 21:42:00 2014 +0100
+
+    Really fix '--cipher none' regression
+    
+    ... by not incorrectly hinting to the compiler the function argument of
+    cipher_kt_mode_{cbc,ofb_cfb}() is nonnull, since that no longer is the
+    case.
+    
+    Verified the fix on Debian Wheezy, one of the platforms the reporter in
+    trac #473 mentions with a compiler that would optimize out the required
+    checks.
+    
+    Also add a testcase for --cipher none to t_lpback, to prevent further
+    regressions.
+    
+    Signed-off-by: Steffan Karger <steffan@karger.me>
+    Acked-by: Gert Doering <gert@greenie.muc.de>
+    Message-Id: <1417552920-31770-1-git-send-email-steffan@karger.me>
+    URL: http://article.gmane.org/gmane.network.openvpn.devel/9300
+    Signed-off-by: Gert Doering <gert@greenie.muc.de>
+
+--- a/src/openvpn/crypto_backend.h
++++ b/src/openvpn/crypto_backend.h
+@@ -237,8 +237,7 @@ int cipher_kt_mode (const cipher_kt_t *c
+  *
+  * @return		true iff the cipher is a CBC mode cipher.
+  */
+-bool cipher_kt_mode_cbc(const cipher_kt_t *cipher)
+-  __attribute__((nonnull));
++bool cipher_kt_mode_cbc(const cipher_kt_t *cipher);
+ 
+ /**
+  * Check if the supplied cipher is a supported OFB or CFB mode cipher.
+@@ -247,8 +246,7 @@ bool cipher_kt_mode_cbc(const cipher_kt_
+  *
+  * @return		true iff the cipher is a OFB or CFB mode cipher.
+  */
+-bool cipher_kt_mode_ofb_cfb(const cipher_kt_t *cipher)
+-  __attribute__((nonnull));
++bool cipher_kt_mode_ofb_cfb(const cipher_kt_t *cipher);
+ 
+ 
+ /**
+--- a/tests/t_lpback.sh
++++ b/tests/t_lpback.sh
+@@ -35,6 +35,9 @@ CIPHERS=$(${top_builddir}/src/openvpn/op
+ # GD, 2014-07-06 do not test RC5-* either (fails on NetBSD w/o libcrypto_rc5)
+ CIPHERS=$(echo "$CIPHERS" | egrep -v '^(DES-EDE3-CFB1|DES-CFB1|RC5-)' )
+ 
++# Also test cipher 'none'
++CIPHERS=${CIPHERS}$(printf "\nnone")
++
+ "${top_builddir}/src/openvpn/openvpn" --genkey --secret key.$$
+ set +e
+