On Mon, Jan 4, 2016 at 5:17 PM, David Howells <dhowells@xxxxxxxxxx> wrote:
> 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@xxxxxxxxxx>
> Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
> Acked-By: David Woodhouse <David.Woodhouse@xxxxxxxxx>
> cc: stable@xxxxxxxxxxxxxxx
> ---
>
> 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 021d39c0ba75..13c4e5a5fe8c 100644
> --- a/crypto/asymmetric_keys/x509_cert_parser.c
> +++ b/crypto/asymmetric_keys/x509_cert_parser.c
> @@ -494,7 +494,7 @@ 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;
> @@ -540,9 +540,9 @@ 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;
> }
> }
> }
>
Looks good. In particular this is a lot more legible than
before, as it now reads exactly like the leap year rules everyone
knows.
A small nit: could it be that the month_lengths array also exists
elsewhere in the kernel? Can it possibly be shared? A quick
glance around didn't pop up anything that's not static, so, looks
like it's okay to add yet another one...
Best regards,
Rudolf Polzer
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