pgsql: Avoid passing unintended format codes to snprintf().

Avoid passing unintended format codes to snprintf().

timeofday() assumed that the output of pg_strftime() could not contain
% signs, other than the one it explicitly asks for with %%. However,
we don't have that guarantee with respect to the time zone name (%Z).
A crafted time zone setting could abuse the subsequent snprintf()
call, resulting in crashes or disclosure of server memory.

To fix, split the pg_strftime() call into two and then treat the
outputs as literal strings, not a snprintf format string. The
extra pg_strftime() call doesn't really cost anything, since the
bulk of the conversion work was done by pg_localtime().

Also, adjust buffer widths so that we're not risking string truncation
during the snprintf() step, as that would create a hazard of producing
mis-encoded output.

This also fixes a latent portability issue: the format string expects
an int, but tp.tv_usec is long int on many platforms.

Reported-by: Xint Code
Author: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Reviewed-by: John Naylor <johncnaylorls(at)gmail(dot)com>
Backpatch-through: 14
Security: CVE-2026-6474

Branch
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REL_18_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/ba27389c2cfa1485bbe26754b23d3f6b4c4e72e2
Author: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>

Modified Files
--------------
src/backend/utils/adt/timestamp.c | 14 +++++++++-----
1 file changed, 9 insertions(+), 5 deletions(-)