Patch "X.509: Fix leap year handling again" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

X.509: Fix leap year handling again

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
x.509-fix-leap-year-handling-again.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: David Howells <[email protected]>
Date: Wed, 24 Feb 2016 14:37:15 +0000
Subject: X.509: Fix leap year handling again

From: David Howells <[email protected]>

commit ac4cbedfdf55455b4c447f17f0fa027dbf02b2a6 upstream.

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.

---
 crypto/asymmetric_keys/x509_cert_parser.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

@@ -494,7 +494,7 @@ int x509_decode_time(time64_t *_t,  size
 		     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;

@@ -540,9 +540,9 @@ int x509_decode_time(time64_t *_t,  size
 		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;
 			}
 		}
 	}

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/x.509-fix-leap-year-handling-again.patch