date: avoid crash on invalid time

[emaste]

Summary

localtime(3) returns NULL when passed an invalid time_t but date(1) previously did not handle it. Exit with an error in that case.

PR:             220828
Reported by:    Vinícius Zavam

[cem]

bin/date/date.c

177–180

This changes the behavior of the code in the success case. Previously we copied the struct tm and modified the local copy. Now we're modifying whatever localtime() gave us, which I suspect is some global storage?

[emaste]

bin/date/date.c

177–180

Yes. Note that setthetime() already modifies the returned struct tm.

[cem]

bin/date/date.c

169

This path can also dereference the pointer returned from localtime() without checking for NULL.

177–180

Ok.

214–215

(See here.)

[emaste]

check an additional localtime for NULL return

[cem]

bin/date/date.c

215

Syntax seems wrong and ld not lt.

[emaste]

correct retypeo from previous upload