MODSIGN: Fix 32-bit overflow in X.509 certificate validity date checking

The current choice of lifetime for the autogenerated X.509 of 100 years,
putting the validTo date in 2112, causes problems on 32-bit systems where a
32-bit time_t wraps in 2106.  64-bit x86_64 systems seem to be unaffected.

This can result in something like:

	Loading module verification certificates
	X.509: Cert 6e03943da0f3b015ba6ed7f5e0cac4fe48680994 has expired
	MODSIGN: Problem loading in-kernel X.509 certificate (-127)

Or:

	X.509: Cert 6e03943da0f3b015ba6ed7f5e0cac4fe48680994 is not yet valid
	MODSIGN: Problem loading in-kernel X.509 certificate (-129)

Instead of turning the dates into time_t values and comparing, turn the system
clock and the ASN.1 dates into tm structs and compare those piecemeal instead.

Reported-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Josh Boyer <jwboyer@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

crypto/asymmetric_keys/x509_cert_parser.c

@@ -434,11 +434,10 @@ int x509_process_extension(void *context, size_t hdrlen,
 /*
  * Record a certificate time.
  */
-static int x509_note_time(time_t *_time,  size_t hdrlen,
+static int x509_note_time(struct tm *tm,  size_t hdrlen,
 			  unsigned char tag,
 			  const unsigned char *value, size_t vlen)
 {
-	unsigned YY, MM, DD, hh, mm, ss;
 	const unsigned char *p = value;
 
 #define dec2bin(X) ((X) - '0')
@@ -448,30 +447,30 @@ static int x509_note_time(time_t *_time,  size_t hdrlen,
 		/* UTCTime: YYMMDDHHMMSSZ */
 		if (vlen != 13)
 			goto unsupported_time;
-		YY = DD2bin(p);
+		tm->tm_year = DD2bin(p);
-		if (YY > 50)
+		if (tm->tm_year >= 50)
-			YY += 1900;
+			tm->tm_year += 1900;
 		else
-			YY += 2000;
+			tm->tm_year += 2000;
 	} else if (tag == ASN1_GENTIM) {
 		/* GenTime: YYYYMMDDHHMMSSZ */
 		if (vlen != 15)
 			goto unsupported_time;
-		YY = DD2bin(p) * 100 + DD2bin(p);
+		tm->tm_year = DD2bin(p) * 100 + DD2bin(p);
 	} else {
 		goto unsupported_time;
 	}
 
-	MM = DD2bin(p);
+	tm->tm_year -= 1900;
-	DD = DD2bin(p);
+	tm->tm_mon  = DD2bin(p) - 1;
-	hh = DD2bin(p);
+	tm->tm_mday = DD2bin(p);
-	mm = DD2bin(p);
+	tm->tm_hour = DD2bin(p);
-	ss = DD2bin(p);
+	tm->tm_min  = DD2bin(p);
+	tm->tm_sec  = DD2bin(p);
 
 	if (*p != 'Z')
 		goto unsupported_time;
 
-	*_time = mktime(YY, MM, DD, hh, mm, ss);
 	return 0;
 
 unsupported_time:

crypto/asymmetric_keys/x509_parser.h

@@ -18,8 +18,8 @@ struct x509_certificate {
 	char		*subject;		/* Name of certificate subject */
 	char		*fingerprint;		/* Key fingerprint as hex */
 	char		*authority;		/* Authority key fingerprint as hex */
-	time_t		valid_from;
+	struct tm	valid_from;
-	time_t		valid_to;
+	struct tm	valid_to;
 	enum pkey_algo	pkey_algo : 8;		/* Public key algorithm */
 	enum pkey_algo	sig_pkey_algo : 8;	/* Signature public key algorithm */
 	enum pkey_hash_algo sig_hash_algo : 8;	/* Signature hash algorithm */

crypto/asymmetric_keys/x509_public_key.c

@@ -106,7 +106,7 @@ static int x509_check_signature(const struct public_key *pub,
 static int x509_key_preparse(struct key_preparsed_payload *prep)
 {
 	struct x509_certificate *cert;
-	time_t now;
+	struct tm now;
 	size_t srlen, sulen;
 	char *desc = NULL;
 	int ret;
@@ -118,7 +118,14 @@ static int x509_key_preparse(struct key_preparsed_payload *prep)
 	pr_devel("Cert Issuer: %s\n", cert->issuer);
 	pr_devel("Cert Subject: %s\n", cert->subject);
 	pr_devel("Cert Key Algo: %s\n", pkey_algo[cert->pkey_algo]);
-	pr_devel("Cert Valid: %lu - %lu\n", cert->valid_from, cert->valid_to);
+	printk("Cert Valid From: %04ld-%02d-%02d %02d:%02d:%02d\n",
+		 cert->valid_from.tm_year + 1900, cert->valid_from.tm_mon + 1,
+		 cert->valid_from.tm_mday, cert->valid_from.tm_hour,
+		 cert->valid_from.tm_min,  cert->valid_from.tm_sec);
+	printk("Cert Valid To: %04ld-%02d-%02d %02d:%02d:%02d\n",
+		 cert->valid_to.tm_year + 1900, cert->valid_to.tm_mon + 1,
+		 cert->valid_to.tm_mday, cert->valid_to.tm_hour,
+		 cert->valid_to.tm_min,  cert->valid_to.tm_sec);
 	pr_devel("Cert Signature: %s + %s\n",
 		 pkey_algo[cert->sig_pkey_algo],
 		 pkey_hash_algo[cert->sig_hash_algo]);
@@ -130,13 +137,38 @@ static int x509_key_preparse(struct key_preparsed_payload *prep)
 		goto error_free_cert;
 	}
 
-	now = CURRENT_TIME.tv_sec;
+	time_to_tm(CURRENT_TIME.tv_sec, 0, &now);
-	if (now < cert->valid_from) {
+	printk("Now: %04ld-%02d-%02d %02d:%02d:%02d\n",
+		 now.tm_year + 1900, now.tm_mon + 1, now.tm_mday,
+		 now.tm_hour, now.tm_min,  now.tm_sec);
+	if (now.tm_year < cert->valid_from.tm_year ||
+	    (now.tm_year == cert->valid_from.tm_year &&
+	     (now.tm_mon < cert->valid_from.tm_mon ||
+	      (now.tm_mon == cert->valid_from.tm_mon &&
+	       (now.tm_mday < cert->valid_from.tm_mday ||
+		(now.tm_mday == cert->valid_from.tm_mday &&
+		 (now.tm_hour < cert->valid_from.tm_hour ||
+		  (now.tm_hour == cert->valid_from.tm_hour &&
+		   (now.tm_min < cert->valid_from.tm_min ||
+		    (now.tm_min == cert->valid_from.tm_min &&
+		     (now.tm_sec < cert->valid_from.tm_sec
+		      ))))))))))) {
 		pr_warn("Cert %s is not yet valid\n", cert->fingerprint);
 		ret = -EKEYREJECTED;
 		goto error_free_cert;
 	}
-	if (now >= cert->valid_to) {
+	if (now.tm_year > cert->valid_to.tm_year ||
+	    (now.tm_year == cert->valid_to.tm_year &&
+	     (now.tm_mon > cert->valid_to.tm_mon ||
+	      (now.tm_mon == cert->valid_to.tm_mon &&
+	       (now.tm_mday > cert->valid_to.tm_mday ||
+		(now.tm_mday == cert->valid_to.tm_mday &&
+		 (now.tm_hour > cert->valid_to.tm_hour ||
+		  (now.tm_hour == cert->valid_to.tm_hour &&
+		   (now.tm_min > cert->valid_to.tm_min ||
+		    (now.tm_min == cert->valid_to.tm_min &&
+		     (now.tm_sec > cert->valid_to.tm_sec
+		      ))))))))))) {
 		pr_warn("Cert %s has expired\n", cert->fingerprint);
 		ret = -EKEYEXPIRED;
 		goto error_free_cert;