pgsql: Prevent stack overflow in json-related functions.

Prevent stack overflow in json-related functions.

Sufficiently-deep recursion heretofore elicited a SIGSEGV.  If an
application constructs PostgreSQL json or jsonb values from arbitrary
user input, application users could have exploited this to terminate all
active database connections.  That applies to 9.3, where the json parser
adopted recursive descent, and later versions.  Only row_to_json() and
array_to_json() were at risk in 9.2, both in a non-security capacity.
Back-patch to 9.2, where the json type was introduced.

Oskari Saarenmaa, reviewed by Michael Paquier.

Security: CVE-2015-5289

Branch
------
REL9_4_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/16d58b5b534fa783e2259b407c237fc166ebf7e4

Modified Files
--------------
src/backend/utils/adt/json.c          |    6 ++++++
src/test/regress/expected/json.out    |    9 +++++++++
src/test/regress/expected/json_1.out  |    9 +++++++++
src/test/regress/expected/jsonb.out   |    9 +++++++++
src/test/regress/expected/jsonb_1.out |    9 +++++++++
src/test/regress/sql/json.sql         |    6 ++++++
src/test/regress/sql/jsonb.sql        |    6 ++++++
7 files changed, 54 insertions(+)