Fix integer overflow UB in timelib

[nielsdos]

There are edge cases where computations can cause an integer overflow, which is undefined behaviour. Lately, some fuzzers seem to be hitting these quite frequently. While this behaviour is undefined, it doesn't actually matter in practice, the worst effect is having a wrong computation result, but no sane person would do computations on e.g. the year pow(2,63).

Still, undefined behaviour is bad.
Make the wrapping behaviour defined by using -fwrapv when possible. The scope of this is limited to timelib and doesn't affect php_date.c.

The reason for this is that this may in theory prevent some optimizations and it also seems bad to affect code that lives so close to the PHP-native edge.

I tested all issues.
This fixes all but 2 issues, the remaining 2 issues are in php_date.c.

Fixes GH-13881.
Fixes GH-14075.
Fixes GH-15150.
Fixes GH-16034.
Fixes GH-16035.
Fixes GH-16048.
Fixes GH-16050.
Fixes GH-16051.
Fixes GH-16052.
Fixes GH-16775.
Fixes GH-16864.
Fixes GH-16865.
Fixes GH-16975.
Fixes GH-17025.
Fixes GH-17059.

cc @derickr @iluuu1994 @Girgias @petk

[Girgias]

I don't know about the build system changes, but adding this compiler flags makes sense to me.

[iluuu1994]

Waiting for somebody else to verify the autoconf part, but adding -fwrapv in general makes sense to me. Unfortunately it's not supported by MSVC, but at least we can avoid undefined behavior with GCC and Clang. The performance impact should be negligible.

[cmb69]

Thank you very much! A great pragmatic solution. Maybe add

 ext/date/config.w32 | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/ext/date/config.w32 b/ext/date/config.w32
index b053e27aae..3dad8d438c 100644
--- a/ext/date/config.w32
+++ b/ext/date/config.w32
@@ -5,6 +5,9 @@ PHP_DATE = "yes";
 ADD_SOURCES("ext/date/lib", "astro.c timelib.c dow.c parse_date.c parse_posix.c parse_tz.c tm2unixtime.c unixtime2tm.c parse_iso_intervals.c interval.c", "date");
 
 ADD_FLAG('CFLAGS_DATE', "/wd4244");
+if (CLANG_TOOLSET) {
+    ADD_FLAG('CFLAGS_BD_EXT_DATE_LIB', "-fwrapv");
+}
 
 var tl_config = FSO.CreateTextFile("ext/date/lib/timelib_config.h", true);
 tl_config.WriteLine("#include \"config.w32.h\"");

just in case someone fuzzes on Windows with Clang (MSVC doesn't support UBSan anyway). This is a hack, though, since ADD_SOURCES doesn't support the special-flags argument, but should do for now.

[derickr]

Looks good to me. Out of interest, which are the two php_date.c ones still failing?

[derickr]

I'm sure this is fine, but of course -DZEND_ENABLE_STATIC_TSRMC_CACHE=1 is meaningless in the PHP_TIMELIB_CFLAGS definition?

[nielsdos]

Yes you are right, I'll move that one too.
Furthermore, I'll apply cmb's suggestion of applying fwrapv to Clang on Windows too.

[nielsdos]

Looks good to me. Out of interest, which are the two php_date.c ones still failing?

Oops, I can't count apparently!

It's only one: #14709 but it has an open PR: #14710 and the PR looks simple enough