timezone: handle truncated timezones from tzcode-2021d and later (BZ #28707)

When using a timezone file with a truncated starting time,
generated by the zic in IANA tzcode-2021d a.k.a. tzlib-2021d
(also in tzlib-2021e; current as of this writing), glibc
asserts in __tzfile_read (on e.g. tzset() for this file) and
you may find lines matching "tzfile.c:435: __tzfile_read:
Assertion `num_types == 1' failed" in your syslog.

One example of such a file is the tzfile for Asuncion
generated by tzlib-2021e as follows, using the tzlib-2021e zic:
"zic -d DEST -r @1546300800 -L /dev/null -b slim
SOURCE/southamerica".  Note that in its type 2 header, it has
two entries in its "time-types" array (types), but only one
entry in its "transition types" array (type_idxs).

This is valid and expected already in the published RFC8536, and
not even frowned upon: "Local time for timestamps before the
first transition is specified by the first time type (time type
0)" ... "every nonzero local time type index SHOULD appear at
least once in the transition type array".  Note the "nonzero ...
index".  Until the 2021d zic, index 0 has been shared by the
first valid transition but with 2021d it's separate, set apart
as a placeholder and only "implicitly" indexed.  (A draft update
of the RFC mandates that the entry at index 0 is a placeholder
in this case, hence can no longer be shared.)

	* time/tzfile.c (__tzfile_read): Don't assert when no transitions
	are found.

Co-authored-by: Christopher Wong <Christopher.Wong@axis.com>
(cherry picked from commit c36f64aa6dff13b12a1e03a185e75a50fa9f6a4c)

diff --git a/NEWS b/NEWS
index 22154086774a1e0cda5746047156595d627c0e5c..5c253a4392339f15f4747e28e4dad36994c1f555 100644 (file)
--- a/NEWS
+++ b/NEWS
@@ -28,6 +28,7 @@ The following bugs are resolved with this release:
   [28702] RISC-V: clone does not align stack
   [28703] RISC-V: _dl_init might be called with unaligned stack
   [28704] elf/tst-cpu-features-cpuinfo fails for KVM guests on some AMD systems
+  [28707] assert in tzfile.c __tzfile_read striking with truncated timezones
   [28744] A64FX string functions are selected without SVE HWCAP
 
 \f

diff --git a/time/tzfile.c b/time/tzfile.c
index 190a777152b31cee5d90d2dc6bc784cd2c904d97..8668392ad387af053565b84f8d1b39f77b33f873 100644 (file)
--- a/time/tzfile.c
+++ b/time/tzfile.c
@@ -431,8 +431,8 @@ __tzfile_read (const char *file, size_t extra, char **extrap)
   if (__tzname[0] == NULL)
     {
       /* This should only happen if there are no transition rules.
-        In this case there should be only one single type.  */
-      assert (num_types == 1);
+        In this case there's usually only one single type, unless
+        e.g. the data file has a truncated time-range.  */
       __tzname[0] = __tzstring (zone_names);
     }
   if (__tzname[1] == NULL)