Linux Kernels

X.509: Fix leap year handling again

This change “X.509: Fix leap year handling again” (commit ac4cbed) in Linux kernel is authored by David Howells <dhowells [at] redhat.com> on Wed Feb 24 14:37:15 2016 +0000.

Description of "X.509: Fix leap year handling again"

The change “X.509: Fix leap year handling again” introduces changes as follows.

X.509: Fix leap year handling again

There are still a couple of minor issues in the X.509 leap year handling:

 (1) To avoid doing a modulus-by-400 in addition to a modulus-by-100 when
     determining whether the year is a leap year or not, I divided the year
     by 100 after doing the modulus-by-100, thereby letting the compiler do
     one instruction for both, and then did a modulus-by-4.

     Unfortunately, I then passed the now-modified year value to mktime64()
     to construct a time value.

     Since this isn't a fast path and since mktime64() does a bunch of
     divisions, just condense down to "% 400".  It's also easier to read.

 (2) The default month length for any February where the year doesn't
     divide by four exactly is obtained from the month_length[] array where
     the value is 29, not 28.

     This is fixed by altering the table.

Reported-by: Rudolf Polzer <rpolzer@google.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: David Woodhouse <David.Woodhouse@intel.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
cc: stable@vger.kernel.org

Linux kernel releases containing commit ac4cbed

The Linux kernel releases containing this commit are as follows.

Linux kernel code changes from "X.509: Fix leap year handling again"

There are 8 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.

 crypto/asymmetric_keys/x509_cert_parser.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)
 
diff --git a/crypto/asymmetric_keys/x509_cert_parser.c b/crypto/asymmetric_keys/x509_cert_parser.c
index 7502029e3385..794cf0eac2c9 100644
--- a/crypto/asymmetric_keys/x509_cert_parser.c
+++ b/crypto/asymmetric_keys/x509_cert_parser.c
@@ -471,7 +471,7 @@ int x509_decode_time(time64_t *_t,  size_t hdrlen,
 		     unsigned char tag,
 		     const unsigned char *value, size_t vlen)
 {
-	static const unsigned char month_lengths[] = { 31, 29, 31, 30, 31, 30,
+	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;
@@ -517,9 +517,9 @@ int x509_decode_time(time64_t *_t,  size_t hdrlen,
 		if (year % 4 == 0) {
 			mon_len = 29;
 			if (year % 100 == 0) {
-				year /= 100;
-				if (year % 4 != 0)
-					mon_len = 28;
+				mon_len = 28;
+				if (year % 400 == 0)
+					mon_len = 29;
 			}
 		}
 	}

The commit for this change in Linux stable tree is ac4cbed (patch).

Last modified: 2020/01/11 06:40