Re: How to crash postgres using savepoints

Gavin Sherry <swm(at)linuxworld(dot)com(dot)au> writes:
> On Tue, 3 Aug 2004, Jeff Davis wrote:
>> I have a question for you also. I just posted a patch at about the same
>> time you did (I sent it to pgsql-patches, but I haven't seen it appear
>> yet). Mine was a one-liner (appended to end of this email) and all it
>> did was add a check into the aforementioned line for a non-null target
>> pointer. My patch seemed to work, so I'd like to know why you changed
>> the structure around more. I did notice some things were a little
>> cleaner, so was it just clean-up or does my patch fail in some way?

> Just a clean up.

Actually, there's an easier fix than either of these, which is just to
pull the savepointLevel test out of the loop and only do it after we've
found a candidate savepoint. There's no point in checking the level at
every loop iteration (especially since the feature isn't even being used
yet, as noted).

Attached is the patch I just applied (which also includes my own notions
about how to make the loop prettier...)

regards, tom lane

*** src/backend/access/transam/xact.c.orig Sun Aug 1 16:57:59 2004
--- src/backend/access/transam/xact.c Tue Aug 3 11:53:41 2004
***************
*** 2520,2541 ****

Assert(PointerIsValid(name));

! target = CurrentTransactionState;
!
! while (target != NULL)
{
if (PointerIsValid(target->name) && strcmp(target->name, name) == 0)
break;
- target = target->parent;
-
- /* we don't cross savepoint level boundaries */
- if (target->savepointLevel != s->savepointLevel)
- ereport(ERROR,
- (errcode(ERRCODE_S_E_INVALID_SPECIFICATION),
- errmsg("no such savepoint")));
}

if (!PointerIsValid(target))
ereport(ERROR,
(errcode(ERRCODE_S_E_INVALID_SPECIFICATION),
errmsg("no such savepoint")));
--- 2520,2538 ----

Assert(PointerIsValid(name));

! for (target = s; PointerIsValid(target); target = target->parent)
{
if (PointerIsValid(target->name) && strcmp(target->name, name) == 0)
break;
}

if (!PointerIsValid(target))
+ ereport(ERROR,
+ (errcode(ERRCODE_S_E_INVALID_SPECIFICATION),
+ errmsg("no such savepoint")));
+
+ /* disallow crossing savepoint level boundaries */
+ if (target->savepointLevel != s->savepointLevel)
ereport(ERROR,
(errcode(ERRCODE_S_E_INVALID_SPECIFICATION),
errmsg("no such savepoint")));