[PATCH v2] timezone: handle truncated timezones from tzcode-2021d and later (BZ #28707)

[Paul Eggert]

On 12/17/21 06:24, Carlos O'Donell wrote:
> What is the impact of this for all of the downstream distributions?

For tzdb Zones, this should affect only people who use zic's -r option 
to limit the size of the TZif binary files by supporting only a 
particular time range. For example, 'zic -r@1609459200 ...' means "omit 
all data for timestamps before the year 2021 UTC". Although full distros 
don't do that, I suppose some stripped-down installions might, for 
embedded applications that don't deal with timestamps in the past. zic's 
-r option was introduced in tzdb 2019a (2019-03-25), was propagated into 
glibc 2.32 (2020-08-05), and is the basis for BZ#28707.

If people are using glibc zic, they need to also specify '-b slim' to 
get the slimmed-down TZif files that have the problem, as in the 
original BZ#28707 bug report. However, I expect that people who use -r 
to generate small TZif files will also either use '-b slim', or will use 
upstream zic where '-b slim' is already the default (this is as of tzdb 
2020b).

> I would like to avoid having every distribution scrambling to patch
> glibc to handle new tdata binary files, but if we need to do this
> patch I would like to get it into all of the active release branches.

That depends on how many people trim down TZif files in the 
abovementioned ways. It shouldn't be a problem on mainstream distros. It 
might be a problem if people use these newer RFC 8536-inspired zic 
options for installations on embedded devices or whatever.