Initialize random() in bootstrap/stand-alone postgres and in initdb.

This removes a difference between the standard IsUnderPostmaster
execution environment and that of --boot and --single.  In a stand-alone
backend, "SELECT random()" always started at the same seed.

On a system capable of using posix shared memory, initdb could still
conclude "selecting dynamic shared memory implementation ... sysv".
Crashed --boot or --single postgres processes orphaned shared memory
objects having names that collided with the not-actually-random names
that initdb probed.  The sysv fallback appeared after ten crashes of
--boot or --single postgres.  Since --boot and --single are rare in
production use, systems used for PostgreSQL development are the
principal candidate to notice this symptom.

Back-patch to 9.3 (all supported versions).  PostgreSQL 9.4 introduced
dynamic shared memory, but 9.3 does share the "SELECT random()" problem.

Reviewed by Tom Lane and Kyotaro HORIGUCHI.

Discussion: https://postgr.es/m/20180915221546.GA3159382@rfd.leadboat.com
This commit is contained in:
Noah Misch 2018-09-23 22:56:39 -07:00
parent 73a6005137
commit d18f6674bd
2 changed files with 11 additions and 0 deletions

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@ -325,6 +325,14 @@ InitStandaloneProcess(const char *argv0)
MyStartTime = time(NULL); /* set our start time in case we call elog */ MyStartTime = time(NULL); /* set our start time in case we call elog */
/*
* Initialize random() for the first time, like PostmasterMain() would.
* In a regular IsUnderPostmaster backend, BackendRun() computes a
* high-entropy seed before any user query. Fewer distinct initial seeds
* can occur here.
*/
srandom((unsigned int) (MyProcPid ^ MyStartTime));
/* Initialize process-local latch support */ /* Initialize process-local latch support */
InitializeLatchSupport(); InitializeLatchSupport();
MyLatch = &LocalLatchData; MyLatch = &LocalLatchData;

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@ -923,6 +923,9 @@ choose_dsm_implementation(void)
#ifdef HAVE_SHM_OPEN #ifdef HAVE_SHM_OPEN
int ntries = 10; int ntries = 10;
/* Initialize random(); this function is its only user in this program. */
srandom((unsigned int) (getpid() ^ time(NULL)));
while (ntries > 0) while (ntries > 0)
{ {
uint32 handle; uint32 handle;