linux-kernel - [PATCH 3/5] X.509: Support leap seconds

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Date:	Fri, 18 Dec 2015 00:02:09 +0000
From:	David Howells <dhowells@...hat.com>
To:	keyrings@...r.kernel.org
Cc:	David Woodhouse <David.Woodhouse@...el.com>,
	Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org,
	stable@...r.kernel.org, dhowells@...hat.com,
	linux-security-module@...r.kernel.org,
	Rudolf Polzer <rpolzer@...gle.com>,
	John Stultz <john.stultz@...aro.org>
Subject: [PATCH 3/5] X.509: Support leap seconds

The format of ASN.1 GeneralizedTime seems to be specified by ISO 8601
[X.680 46.3] and this apparently supports leap seconds (ie. the seconds
field is 60).  It's not entirely clear that ASN.1 expects it, but we can
relax the seconds check slightly for GeneralizedTime.

This, however, results in us passing a time with sec as 60 to mktime64()
which, unpatched, doesn't really handle such things.  What it will do is
equate the 60th second of a minute to the 0th second of the next minute.

We can't really do otherwise without giving the kernel much greater
knowledge of where all the leap seconds are.  Unfortunately, this would
require change the mapping of the kernel's current-time-in-seconds.

UTCTime, however, only supports a seconds value in the range 00-59.

Without this patch, certain X.509 certificates will be rejected,
potentially making a kernel unbootable.

Reported-by: Rudolf Polzer <rpolzer@...gle.com>
Signed-off-by: David Howells <dhowells@...hat.com>
cc: David Woodhouse <David.Woodhouse@...el.com>
cc: John Stultz <john.stultz@...aro.org>
cc: Arnd Bergmann <arnd@...db.de>
cc: stable@...r.kernel.org
---

 crypto/asymmetric_keys/x509_cert_parser.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/crypto/asymmetric_keys/x509_cert_parser.c b/crypto/asymmetric_keys/x509_cert_parser.c
index 13c4e5a5fe8c..9be2caebc57b 100644
--- a/crypto/asymmetric_keys/x509_cert_parser.c
+++ b/crypto/asymmetric_keys/x509_cert_parser.c
@@ -497,7 +497,7 @@ int x509_decode_time(time64_t *_t,  size_t hdrlen,
 	static const unsigned char month_lengths[] = { 31, 28, 31, 30, 31, 30,
 						       31, 31, 30, 31, 30, 31 };
 	const unsigned char *p = value;
-	unsigned year, mon, day, hour, min, sec, mon_len;
+	unsigned year, mon, day, hour, min, sec, mon_len, max_sec;
 
 #define dec2bin(X) ({ unsigned char x = (X) - '0'; if (x > 9) goto invalid_time; x; })
 #define DD2bin(P) ({ unsigned x = dec2bin(P[0]) * 10 + dec2bin(P[1]); P += 2; x; })
@@ -511,6 +511,7 @@ int x509_decode_time(time64_t *_t,  size_t hdrlen,
 			year += 1900;
 		else
 			year += 2000;
+		max_sec = 59;
 	} else if (tag == ASN1_GENTIM) {
 		/* GenTime: YYYYMMDDHHMMSSZ */
 		if (vlen != 15)
@@ -518,6 +519,7 @@ int x509_decode_time(time64_t *_t,  size_t hdrlen,
 		year = DD2bin(p) * 100 + DD2bin(p);
 		if (year >= 1950 && year <= 2049)
 			goto invalid_time;
+		max_sec = 60; /* ISO 8601 permits leap seconds [X.680 46.3] */
 	} else {
 		goto unsupported_time;
 	}
@@ -550,7 +552,7 @@ int x509_decode_time(time64_t *_t,  size_t hdrlen,
 	if (day < 1 || day > mon_len ||
 	    hour > 23 ||
 	    min > 59 ||
-	    sec > 59)
+	    sec > max_sec)
 		goto invalid_time;
 
 	*_t = mktime64(year, mon, day, hour, min, sec);

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