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Date: Fri, 14 Sep 2018 21:16:34 -0400
From: Rich Felker <dalias@...c.org>
To: musl@...ts.openwall.com
Subject: Re: [PATCH] always reset DST rules during tzset
On Fri, Sep 14, 2018 at 03:46:55PM -0700, Benjamin Peterson wrote:
> do_tzset() did't always reset the DST transition rules r0 and r1. That means the
> rules from older TZ settings could leak into newer ones.
>
> The following program demonstrates this bug. It should print out the same
> timezone twice but doesn't due to the leaky state.
>
> int main() {
> time_t t = 0;
> struct tm p;
> setenv("TZ", "STD-1DST", 1);
> localtime_r(&t, &p);
> printf("%s\n", p.tm_zone);
> setenv("TZ", "STD-1DST,M3.2.0,M11.1.0", 1);
> tzset();
> setenv("TZ", "STD-1DST", 1);
> localtime_r(&t, &p);
> printf("%s\n", p.tm_zone);
> return 0;
> }
> ---
> src/time/__tz.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/src/time/__tz.c b/src/time/__tz.c
> index 51e66514..3ccfdd5d 100644
> --- a/src/time/__tz.c
> +++ b/src/time/__tz.c
> @@ -130,6 +130,9 @@ static void do_tzset()
>
> if (old_tz && !strcmp(s, old_tz)) return;
>
> + memset(r0, 0, sizeof r0);
> + memset(r1, 0, sizeof r1);
> +
> if (zi) __munmap((void *)zi, map_size);
>
> /* Cache the old value of TZ to check if it has changed. Avoid
> @@ -194,7 +197,6 @@ static void do_tzset()
> const unsigned char *p;
> __tzname[0] = __tzname[1] = 0;
> __daylight = __timezone = dst_off = 0;
> - for (i=0; i<5; i++) r0[i] = r1[i] = 0;
> for (p=types; p<abbrevs; p+=6) {
> if (!p[4] && !__tzname[0]) {
> __tzname[0] = (char *)abbrevs + p[5];
> --
> 2.17.1
This looks right, but is there a reason you swapped the for loop out
for memsets? Either should work, but I probably preferred the loop in
the original since, due to -ffreestanding which is necessary when
building a libc, the compiler can't inline the memset automatically
with a builtin. I might however use the new header wrapper framework
to make it so (dependent on __GNUC__) memcpy and memset get redirected
to the __builtin_* versions except in the source files that define
them, in which case this kind of thing wouldn't matter.
Rich
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