ASN.1: Handle 'ANY OPTIONAL' in grammar

An ANY object in an ASN.1 grammar that is marked OPTIONAL should be skipped
if there is no more data to be had.

This can be tested by editing X.509 certificates or PKCS#7 messages to
remove the NULL from subobjects that look like the following:

SEQUENCE {
OBJECT(2a864886f70d01010b);
NULL();
}

This is an algorithm identifier plus an optional parameter.

The modified DER can be passed to one of:

keyctl padd asymmetric "" @s </tmp/modified.x509
keyctl padd pkcs7_test foo @s </tmp/modified.pkcs7

It should work okay with the patch and produce EBADMSG without.

Signed-off-by: David Howells <[e-mail]>
Tested-by: Marcel Holtmann <[e-mail]>
Reviewed-by: David Woodhouse <[e-mail]>

include/linux/asn1_ber_bytecode.h

···
 	ASN1_OP_MATCH_JUMP		= 0x04,
 	ASN1_OP_MATCH_JUMP_OR_SKIP	= 0x05,
 	ASN1_OP_MATCH_ANY		= 0x08,
+	ASN1_OP_MATCH_ANY_OR_SKIP	= 0x09,
 	ASN1_OP_MATCH_ANY_ACT		= 0x0a,
+	ASN1_OP_MATCH_ANY_ACT_OR_SKIP	= 0x0b,
 	/* Everything before here matches unconditionally */
 
 	ASN1_OP_COND_MATCH_OR_SKIP	= 0x11,
 	ASN1_OP_COND_MATCH_ACT_OR_SKIP	= 0x13,
 	ASN1_OP_COND_MATCH_JUMP_OR_SKIP	= 0x15,
 	ASN1_OP_COND_MATCH_ANY		= 0x18,
+	ASN1_OP_COND_MATCH_ANY_OR_SKIP	= 0x19,
 	ASN1_OP_COND_MATCH_ANY_ACT	= 0x1a,
+	ASN1_OP_COND_MATCH_ANY_ACT_OR_SKIP = 0x1b,
 
 	/* Everything before here will want a tag from the data */
-#define ASN1_OP__MATCHES_TAG ASN1_OP_COND_MATCH_ANY_ACT
+#define ASN1_OP__MATCHES_TAG ASN1_OP_COND_MATCH_ANY_ACT_OR_SKIP
 
 	/* These are here to help fill up space */
-	ASN1_OP_COND_FAIL		= 0x1b,
-	ASN1_OP_COMPLETE		= 0x1c,
-	ASN1_OP_ACT			= 0x1d,
-	ASN1_OP_MAYBE_ACT		= 0x1e,
-	ASN1_OP_RETURN			= 0x1f,
+	ASN1_OP_COND_FAIL		= 0x1c,
+	ASN1_OP_COMPLETE		= 0x1d,
+	ASN1_OP_ACT			= 0x1e,
+	ASN1_OP_MAYBE_ACT		= 0x1f,
 
 	/* The following eight have bit 0 -> SET, 1 -> OF, 2 -> ACT */
 	ASN1_OP_END_SEQ			= 0x20,
···
 #define ASN1_OP_END__SET		  0x01
 #define ASN1_OP_END__OF			  0x02
 #define ASN1_OP_END__ACT		  0x04
+
+	ASN1_OP_RETURN			= 0x28,
 
 	ASN1_OP__NR
 };

lib/asn1_decoder.c

···
 	[ASN1_OP_MATCH_JUMP]			= 1 + 1 + 1,
 	[ASN1_OP_MATCH_JUMP_OR_SKIP]		= 1 + 1 + 1,
 	[ASN1_OP_MATCH_ANY]			= 1,
+	[ASN1_OP_MATCH_ANY_OR_SKIP]		= 1,
 	[ASN1_OP_MATCH_ANY_ACT]			= 1         + 1,
+	[ASN1_OP_MATCH_ANY_ACT_OR_SKIP]		= 1         + 1,
 	[ASN1_OP_COND_MATCH_OR_SKIP]		= 1 + 1,
 	[ASN1_OP_COND_MATCH_ACT_OR_SKIP]	= 1 + 1     + 1,
 	[ASN1_OP_COND_MATCH_JUMP_OR_SKIP]	= 1 + 1 + 1,
 	[ASN1_OP_COND_MATCH_ANY]		= 1,
+	[ASN1_OP_COND_MATCH_ANY_OR_SKIP]	= 1,
 	[ASN1_OP_COND_MATCH_ANY_ACT]		= 1         + 1,
+	[ASN1_OP_COND_MATCH_ANY_ACT_OR_SKIP]	= 1         + 1,
 	[ASN1_OP_COND_FAIL]			= 1,
 	[ASN1_OP_COMPLETE]			= 1,
 	[ASN1_OP_ACT]				= 1         + 1,
···
 	/* Decide how to handle the operation */
 	switch (op) {
 	case ASN1_OP_MATCH_ANY_ACT:
+	case ASN1_OP_MATCH_ANY_ACT_OR_SKIP:
 	case ASN1_OP_COND_MATCH_ANY_ACT:
+	case ASN1_OP_COND_MATCH_ANY_ACT_OR_SKIP:
 		ret = actions[machine[pc + 1]](context, hdr, tag, data + dp, len);
 		if (ret < 0)
 			return ret;
···
 	case ASN1_OP_MATCH:
 	case ASN1_OP_MATCH_OR_SKIP:
 	case ASN1_OP_MATCH_ANY:
+	case ASN1_OP_MATCH_ANY_OR_SKIP:
 	case ASN1_OP_COND_MATCH_OR_SKIP:
 	case ASN1_OP_COND_MATCH_ANY:
+	case ASN1_OP_COND_MATCH_ANY_OR_SKIP:
 	skip_data:
 		if (!(flags & FLAG_CONS)) {
 			if (flags & FLAG_INDEFINITE_LENGTH) {

scripts/asn1_compiler.c

···
 	act = e->action ? "_ACT" : "";
 	switch (e->compound) {
 	case ANY:
-		render_opcode(out, "ASN1_OP_%sMATCH_ANY%s,", cond, act);
+		render_opcode(out, "ASN1_OP_%sMATCH_ANY%s%s,",
+			      cond, act, skippable ? "_OR_SKIP" : "");
 		if (e->name)
 			render_more(out, "\t\t// %*.*s",
 				    (int)e->name->size, (int)e->name->size,