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Commitb251379

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Avoid using PostmasterRandom() for DSM control segment ID.
Commits470d886 et al intended to fix the problem that the postmasterselected the same "random" DSM control segment ID on every start. Butusing PostmasterRandom() for that destroys the intended property that thedelay between random_start_time and random_stop_time will be unpredictable.(Said delay is probably already more predictable than we could wish, butthat doesn't mean that reducing it by a couple orders of magnitude is OK.)Revert the previous patch and add a comment warning against misuse ofPostmasterRandom. Fix the original problem by calling srandom() early inPostmasterMain, using a low-security seed that will later be overwrittenby PostmasterRandom.Discussion: <20789.1474390434@sss.pgh.pa.us>
1 parenta88fe25 commitb251379

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3 files changed

+17
-4
lines changed

3 files changed

+17
-4
lines changed

‎src/backend/postmaster/postmaster.c

Lines changed: 16 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -403,6 +403,7 @@ static void processCancelRequest(Port *port, void *pkt);
403403
staticintinitMasks(fd_set*rmask);
404404
staticvoidreport_fork_failure_to_client(Port*port,interrnum);
405405
staticCAC_statecanAcceptConnections(void);
406+
staticlongPostmasterRandom(void);
406407
staticvoidRandomSalt(char*md5Salt);
407408
staticvoidsignal_child(pid_tpid,intsignal);
408409
staticboolSignalSomeChildren(intsignal,inttargets);
@@ -574,6 +575,16 @@ PostmasterMain(int argc, char *argv[])
574575
*/
575576
umask(S_IRWXG |S_IRWXO);
576577

578+
/*
579+
* Initialize random(3) so we don't get the same values in every run.
580+
*
581+
* Note: the seed is pretty predictable from externally-visible facts such
582+
* as postmaster start time, so avoid using random() for security-critical
583+
* random values during postmaster startup. At the time of first
584+
* connection, PostmasterRandom will select a hopefully-more-random seed.
585+
*/
586+
srandom((unsignedint) (MyProcPid ^MyStartTime));
587+
577588
/*
578589
* By default, palloc() requests in the postmaster will be allocated in
579590
* the PostmasterContext, which is space that can be recycled by backends.
@@ -5101,8 +5112,12 @@ RandomSalt(char *md5Salt)
51015112

51025113
/*
51035114
* PostmasterRandom
5115+
*
5116+
* Caution: use this only for values needed during connection-request
5117+
* processing. Otherwise, the intended property of having an unpredictable
5118+
* delay between random_start_time and random_stop_time will be broken.
51045119
*/
5105-
long
5120+
staticlong
51065121
PostmasterRandom(void)
51075122
{
51085123
/*

‎src/backend/storage/ipc/dsm.c

Lines changed: 1 addition & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -36,7 +36,6 @@
3636

3737
#include"lib/ilist.h"
3838
#include"miscadmin.h"
39-
#include"postmaster/postmaster.h"
4039
#include"storage/dsm.h"
4140
#include"storage/ipc.h"
4241
#include"storage/lwlock.h"
@@ -180,7 +179,7 @@ dsm_postmaster_startup(PGShmemHeader *shim)
180179
{
181180
Assert(dsm_control_address==NULL);
182181
Assert(dsm_control_mapped_size==0);
183-
dsm_control_handle=(dsm_handle)PostmasterRandom();
182+
dsm_control_handle=random();
184183
if (dsm_control_handle==0)
185184
continue;
186185
if (dsm_impl_op(DSM_OP_CREATE,dsm_control_handle,segsize,

‎src/include/postmaster/postmaster.h

Lines changed: 0 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -48,7 +48,6 @@ extern const char *progname;
4848

4949
externvoidPostmasterMain(intargc,char*argv[])pg_attribute_noreturn();
5050
externvoidClosePostmasterPorts(boolam_syslogger);
51-
externlongPostmasterRandom(void);
5251

5352
externintMaxLivePostmasterChildren(void);
5453

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