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libsec/x509: fix verify_signature(), digest_certinfo(), X509dump()

make digest_certinfo() return the digest length, otherwise
return -1 as an error and handle it in the callers.

pass expected digest length to verify_signature() and
check digest length from certificate! make sure we wont
run off the buffer.

fix newlines in error prints of X509dump().

--- a/sys/src/libsec/port/x509.c

+++ b/sys/src/libsec/port/x509.c

@@ -2145,7 +2145,7 @@

  * Our ASN.1 library doesn't return pointers into the original

  * data array, so we need to do a little hand decoding.

  */

-static void

+static int

 digest_certinfo(Bytes *cert, DigestAlg *da, uchar *digest)

 {

 	uchar *info, *p, *pend;

@@ -2161,19 +2161,20 @@

 	   length_decode(&p, pend, &length) != ASN_OK ||

 	   p+length > pend ||

 	   p+length < p)

-		return;

+		return -1;

 	info = p;

 	if(ber_decode(&p, pend, &elem) != ASN_OK)

-		return;

+		return -1;

 	freevalfields(&elem.val);

 	if(elem.tag.num != SEQUENCE)

-		return;

+		return -1;

 	infolen = p - info;

 	(*da->fun)(info, infolen, digest, nil);

+	return da->len;

 }

 static char*

-verify_signature(Bytes* signature, RSApub *pk, uchar *edigest, Elem **psigalg)

+verify_signature(Bytes* signature, RSApub *pk, uchar *edigest, int edigestlen, Elem **psigalg)

 {

 	Elem e;

 	Elist *el;

@@ -2199,15 +2200,14 @@

 		err = "expected 1";

 		goto end;

 	}

-	buf++;

-	while(buf[0] == 0xff)

-		buf++;

-	if(buf[0] != 0) {

+	buf++, buflen--;

+	while(buflen > 0 && buf[0] == 0xff)

+		buf++, buflen--;

+	if(buflen < 1 || buf[0] != 0) {

 		err = "expected 0";

 		goto end;

 	}

-	buf++;

-	buflen -= buf-pkcs1buf;

+	buf++, buflen--;

 	if(decode(buf, buflen, &e) != ASN_OK || !is_seq(&e, &el) || elistlen(el) != 2 ||

 			!is_octetstring(&el->tl->hd, &digest)) {

 		err = "signature parse error";

@@ -2214,9 +2214,12 @@

 		goto end;

 	}

 	*psigalg = &el->hd;

-	if(memcmp(digest->data, edigest, digest->len) == 0)

+	if(digest->len != edigestlen) {

+		err = "bad digest length";

 		goto end;

-	err = "digests did not match";

+	}

+	if(memcmp(digest->data, edigest, edigestlen) != 0)

+		err = "digests did not match";

 end:

 	if(pkcs1 != nil)

@@ -2256,17 +2259,23 @@

 	char *e;

 	Bytes *b;

 	CertX509 *c;

-	uchar digest[256];

+	int digestlen;

+	uchar digest[MAXdlen];

 	Elem *sigalg;

 	b = makebytes(cert, ncert);

 	c = decode_cert(b);

-	if(c != nil)

-		digest_certinfo(b, digestalg[c->signature_alg], digest);

-	freebytes(b);

-	if(c == nil)

+	if(c == nil){

+		freebytes(b);

 		return "cannot decode cert";

-	e = verify_signature(c->signature, pk, digest, &sigalg);

+	}

+	digestlen = digest_certinfo(b, digestalg[c->signature_alg], digest);

+	freebytes(b);

+	if(digestlen <= 0){

+		freecert(c);

+		return "cannot decode certinfo";

+	}

+	e = verify_signature(c->signature, pk, digest, digestlen, &sigalg);

 	freecert(c);

 	return e;

 }

@@ -2671,7 +2680,7 @@

 	Bytes *b;

 	CertX509 *c;

 	RSApub *pk;

-	DigestAlg *da;

+	int digestlen;

 	uchar digest[MAXdlen];

 	Elem *sigalg;

@@ -2680,12 +2689,16 @@

 	c = decode_cert(b);

 	if(c == nil){

 		freebytes(b);

-		print("cannot decode cert");

+		print("cannot decode cert\n");

 		return;

 	}

-	da = digestalg[c->signature_alg];

-	digest_certinfo(b, da, digest);

+	digestlen = digest_certinfo(b, digestalg[c->signature_alg], digest);

 	freebytes(b);

+	if(digestlen <= 0){

+		freecert(c);

+		print("cannot decode certinfo\n");

+		return;

+	}

 	print("serial %d\n", c->serial);

 	print("issuer %s\n", c->issuer);

@@ -2694,8 +2707,8 @@

 	pk = decode_rsapubkey(c->publickey);

 	print("pubkey e=%B n(%d)=%B\n", pk->ek, mpsignif(pk->n), pk->n);

-	print("sigalg=%d digest=%.*H\n", c->signature_alg, da->len, digest);

-	e = verify_signature(c->signature, pk, digest, &sigalg);

+	print("sigalg=%d digest=%.*H\n", c->signature_alg, digestlen, digest);

+	e = verify_signature(c->signature, pk, digest, digestlen, &sigalg);

 	if(e==nil){

 		e = "nil (meaning ok)";

 		print("sigalg=\n");