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Commit82ebc70

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Be more wary about 32-bit integer overflow in pg_stat_statements.
We've heard a couple of reports of people having trouble withmulti-gigabyte-sized query-texts files. It occurred to me that on32-bit platforms, there could be an issue with integer overflowof calculations associated with the total query text size.Address that with several changes:1. Limit pg_stat_statements.max to INT_MAX / 2 not INT_MAX.The hashtable code will bound it to that anyway unless "long"is 64 bits. We still need overflow guards on its use, butthis helps.2. Add a check to prevent extending the query-texts file tomore than MaxAllocHugeSize. If it got that big, qtext_load_filewould certainly fail, so there's not much point in allowing it.Without this, we'd need to consider whether extent, query_offset,and related variables shouldn't be off_t not size_t.3. Adjust the comparisons in need_gc_qtexts() to be done in 64-bitarithmetic on all platforms. It appears possible that under duressthose multiplications could overflow 32 bits, yielding a falseconclusion that we need to garbage-collect the texts file, whichcould lead to repeatedly garbage-collecting after every hash tableinsertion.Per report from Bruno da Silva. I'm not convinced that theseissues fully explain his problem; there may be some other bug that'scontributing to the query-texts file becoming so large in the firstplace. But it did get that big, so#2 is a reasonable defense,and#3 could explain the reported performance difficulties.(See also commit8bbe4cb, which addressed some related bugs.The second Discussion: link is the thread that led up to that.)This issue is old, and is primarily a problem for old platforms,so back-patch.Discussion:https://postgr.es/m/CAB+Nuk93fL1Q9eLOCotvLP07g7RAv4vbdrkm0cVQohDVMpAb9A@mail.gmail.comDiscussion:https://postgr.es/m/5601D354.5000703@BlueTreble.com
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‎contrib/pg_stat_statements/pg_stat_statements.c

Lines changed: 22 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -399,7 +399,7 @@ _PG_init(void)
399399
&pgss_max,
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5000,
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100,
402-
INT_MAX,
402+
INT_MAX /2,
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PGC_POSTMASTER,
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0,
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NULL,
@@ -2094,6 +2094,18 @@ qtext_store(const char *query, int query_len,
20942094

20952095
*query_offset=off;
20962096

2097+
/*
2098+
* Don't allow the file to grow larger than what qtext_load_file can
2099+
* (theoretically) handle. This has been seen to be reachable on 32-bit
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* platforms.
2101+
*/
2102+
if (unlikely(query_len >=MaxAllocHugeSize-off))
2103+
{
2104+
errno=EFBIG;/* not quite right, but it'll do */
2105+
fd=-1;
2106+
gotoerror;
2107+
}
2108+
20972109
/* Now write the data into the successfully-reserved part of the file */
20982110
fd=OpenTransientFile(PGSS_TEXT_FILE,O_RDWR |O_CREAT |PG_BINARY);
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if (fd<0)
@@ -2279,8 +2291,14 @@ need_gc_qtexts(void)
22792291
SpinLockRelease(&s->mutex);
22802292
}
22812293

2282-
/* Don't proceed if file does not exceed 512 bytes per possible entry */
2283-
if (extent<512*pgss_max)
2294+
/*
2295+
* Don't proceed if file does not exceed 512 bytes per possible entry.
2296+
*
2297+
* Here and in the next test, 32-bit machines have overflow hazards if
2298+
* pgss_max and/or mean_query_len are large. Force the multiplications
2299+
* and comparisons to be done in uint64 arithmetic to forestall trouble.
2300+
*/
2301+
if ((uint64)extent< (uint64)512*pgss_max)
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return false;
22852303

22862304
/*
@@ -2290,7 +2308,7 @@ need_gc_qtexts(void)
22902308
* query length in order to prevent garbage collection from thrashing
22912309
* uselessly.
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*/
2293-
if (extent<pgss->mean_query_len*pgss_max*2)
2311+
if ((uint64)extent< (uint64)pgss->mean_query_len*pgss_max*2)
22942312
return false;
22952313

22962314
return true;

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