Add test certificate with basicConstraints containing only an INTEGER

The basicConstraints extension contains only an INTEGER. According to
RFC 5280, this should be cA=FALSE and a pathLenConstraint value which is
effectively ignored. But Mbed TLS parses it as cA=TRUE if the integer value
is nonzero.

This certificate is syntactically valid, but RFC 5280 forbids CAs from
emitting it. Compliant X.509 parsers treat it as cA=FALSE.

Signed-off-by: Gilles Peskine <[email protected]>

data_files/Makefile

@@ -2328,6 +2328,22 @@ parse_input/server5.basic-constraints-sequence-overflow.selfsigned.crt: parse_in
 		-inform DER -in $< -outform DER -out $@
 all_final += parse_input/server5.basic-constraints-sequence-overflow.selfsigned.crt
 
+# Replace a well-formed basicConstraints extension containing CA:TRUE with
+# a malformed extension that is empty with trailing junk. The trailing
+# junk is a boolean with the value true, thus it would be interpreted as
+# CA:TRUE if it was properly inside the basicConstraints extension.
+parse_input/server5.basic-constraints-integer-first.badsign.crt: server5-ca.der
+	perl -0777 -pe '$$n = s/\x04\x05\x30\x03\x01\x01\xff/\x04\x05\x30\x03\x02\x01\x01/g; die "More substitutions than expected" if $$n > 1; die "Substitution not found" if $$n < 1' <$< >$@.tmp
+	mv $@.tmp $@
+all_final += parse_input/server5.basic-constraints-integer-first.badsign.crt
+
+parse_input/server5.basic-constraints-integer-first.selfsigned.crt: parse_input/server5.basic-constraints-integer-first.badsign.crt server5.key
+	$(OPENSSL) x509 -subj '/CN=Eve/' \
+		-key server5.key \
+		-days 3653 \
+		-inform DER -in $< -outform DER -out $@
+all_final += parse_input/server5.basic-constraints-integer-first.selfsigned.crt
+
 # MD5 test certificate
 
 cert_md_test_key = $(cli_crt_key_file_rsa)