imap-send: support subjectAltName as well

Check not only the common name of the certificate subject, but also
check the subject alternative DNS names as well, when verifying that
the certificate matches that of the host we are trying to talk to.

Signed-off-by: Oswald Buddenhagen <ossi@kde.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

imap-send.c

@@ -30,6 +30,7 @@ typedef void *SSL;
 #else
 #include <openssl/evp.h>
 #include <openssl/hmac.h>
+#include <openssl/x509v3.h>
 #endif
 
 struct store_conf {
@@ -292,6 +293,24 @@ static int verify_hostname(X509 *cert, const char *hostname)
 	int len;
 	X509_NAME *subj;
 	char cname[1000];
+	int i, found;
+	STACK_OF(GENERAL_NAME) *subj_alt_names;
+
+	/* try the DNS subjectAltNames */
+	found = 0;
+	if ((subj_alt_names = X509_get_ext_d2i(cert, NID_subject_alt_name, NULL, NULL))) {
+		int num_subj_alt_names = sk_GENERAL_NAME_num(subj_alt_names);
+		for (i = 0; !found && i < num_subj_alt_names; i++) {
+			GENERAL_NAME *subj_alt_name = sk_GENERAL_NAME_value(subj_alt_names, i);
+			if (subj_alt_name->type == GEN_DNS &&
+			    strlen((const char *)subj_alt_name->d.ia5->data) == (size_t)subj_alt_name->d.ia5->length &&
+			    host_matches(hostname, (const char *)(subj_alt_name->d.ia5->data)))
+				found = 1;
+		}
+		sk_GENERAL_NAME_pop_free(subj_alt_names, GENERAL_NAME_free);
+	}
+	if (found)
+		return 0;
 
 	/* try the common name */
 	if (!(subj = X509_get_subject_name(cert)))