[Buildroot] [PATCH v4, 1/1] package/uacme: don't allow mbedtls with ualpn

[Fabrice Fontaine <fontaine.fabrice@gmail.com>]

ualpn with mbedtls requires the activation of
MBEDTLS_X509_ALLOW_UNSUPPORTED_CRITICAL_EXTENSION on mbedtls which can
be a security risk.

So let the user explicitly choose the crypto library by copy/pasting
behavior of libssh and don't allow the user to select mbedtls with ualpn

Fixes:
 - http://autobuild.buildroot.org/results/5d42189299549cd655218e9e7cfcfa63e79f74ec

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
---
Changes v3 -> v4:
 - Fix commit title

Changes v2 -> v3 (after review of Yann E. Morin):
 - Put back the option to select crypto backend and do not allow the
   user to select mbedtls with ualpn

Changes v1 -> v2 (after review of Thomas Petazzoni and Yann E. Morin):
 - Do not use ualpn with mbedtls

 package/uacme/Config.in | 24 ++++++++++++++++++++++++
 package/uacme/uacme.mk  |  6 +++---
 2 files changed, 27 insertions(+), 3 deletions(-)

diff --git a/package/uacme/Config.in b/package/uacme/Config.in
index 58b7c534e7..ba60d787f0 100644
--- a/package/uacme/Config.in
+++ b/package/uacme/Config.in
@@ -16,6 +16,30 @@ config BR2_PACKAGE_UACME
 
 if BR2_PACKAGE_UACME
 
+choice
+	prompt "Crypto Backend"
+	help
+	  Select crypto library to be used in uacme.
+
+config BR2_PACKAGE_UACME_GNUTLS
+	bool "gnutls"
+	depends on BR2_PACKAGE_GNUTLS
+
+config BR2_PACKAGE_UACME_MBEDTLS
+	bool "mbedtls"
+	depends on BR2_PACKAGE_MBEDTLS
+	depends on !BR2_PACKAGE_UACME_UALPN
+
+comment "mbedtls crypto backend unavailable with ualpn"
+	depends on BR2_PACKAGE_MBEDTLS
+	depends on BR2_PACKAGE_UACME_UALPN
+
+config BR2_PACKAGE_UACME_OPENSSL
+	bool "openssl"
+	depends on BR2_PACKAGE_OPENSSL
+
+endchoice
+
 config BR2_PACKAGE_UACME_UALPN
 	bool "enable ualpn"
 	depends on BR2_TOOLCHAIN_HAS_THREADS
diff --git a/package/uacme/uacme.mk b/package/uacme/uacme.mk
index 6df13eced6..90c3a24c13 100644
--- a/package/uacme/uacme.mk
+++ b/package/uacme/uacme.mk
@@ -15,13 +15,13 @@ UACME_DEPENDENCIES = libcurl
 
 UACME_CONF_ENV = ac_cv_prog_cc_c99='-std=gnu99'
 
-ifeq ($(BR2_PACKAGE_GNUTLS),y)
+ifeq ($(BR2_PACKAGE_UACME_GNUTLS),y)
 UACME_CONF_OPTS += --with-gnutls
 UACME_DEPENDENCIES += gnutls
-else ifeq ($(BR2_PACKAGE_MBEDTLS),y)
+else ifeq ($(BR2_PACKAGE_UACME_MBEDTLS),y)
 UACME_CONF_OPTS += --with-mbedtls
 UACME_DEPENDENCIES += mbedtls
-else ifeq ($(BR2_PACKAGE_OPENSSL),y)
+else ifeq ($(BR2_PACKAGE_UACME_OPENSSL),y)
 UACME_CONF_OPTS += --with-openssl
 UACME_DEPENDENCIES += openssl
 endif
-- 
2.25.1