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
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REL9_3_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/f8862172e6519b82e66c51baa5b87e29847db2b9

Modified Files
--------------
src/backend/utils/adt/json.c         |    7 +++++++
src/test/regress/expected/json.out   |    9 +++++++++
src/test/regress/expected/json_1.out |    9 +++++++++
src/test/regress/sql/json.sql        |    6 ++++++
4 files changed, 31 insertions(+)